mirror of
https://github.com/RPCS3/llvm-mirror.git
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37951daad5
llvm-svn: 27051
1084 lines
43 KiB
C++
1084 lines
43 KiB
C++
//===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass transforms loops that contain branches on loop-invariant conditions
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// to have multiple loops. For example, it turns the left into the right code:
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//
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// for (...) if (lic)
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// A for (...)
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// if (lic) A; B; C
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// B else
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// C for (...)
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// A; C
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//
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// This can increase the size of the code exponentially (doubling it every time
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// a loop is unswitched) so we only unswitch if the resultant code will be
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// smaller than a threshold.
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//
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// This pass expects LICM to be run before it to hoist invariant conditions out
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// of the loop, to make the unswitching opportunity obvious.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "loop-unswitch"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/PostOrderIterator.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/CommandLine.h"
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#include <algorithm>
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#include <iostream>
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#include <set>
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using namespace llvm;
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namespace {
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Statistic<> NumBranches("loop-unswitch", "Number of branches unswitched");
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Statistic<> NumSwitches("loop-unswitch", "Number of switches unswitched");
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Statistic<> NumSelects ("loop-unswitch", "Number of selects unswitched");
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Statistic<> NumTrivial ("loop-unswitch",
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"Number of unswitches that are trivial");
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Statistic<> NumSimplify("loop-unswitch",
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"Number of simplifications of unswitched code");
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cl::opt<unsigned>
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Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
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cl::init(10), cl::Hidden);
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class LoopUnswitch : public FunctionPass {
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LoopInfo *LI; // Loop information
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// LoopProcessWorklist - List of loops we need to process.
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std::vector<Loop*> LoopProcessWorklist;
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public:
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virtual bool runOnFunction(Function &F);
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bool visitLoop(Loop *L);
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/// This transformation requires natural loop information & requires that
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/// loop preheaders be inserted into the CFG...
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///
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredID(LoopSimplifyID);
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AU.addPreservedID(LoopSimplifyID);
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AU.addRequired<LoopInfo>();
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AU.addPreserved<LoopInfo>();
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}
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private:
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/// RemoveLoopFromWorklist - If the specified loop is on the loop worklist,
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/// remove it.
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void RemoveLoopFromWorklist(Loop *L) {
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std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(),
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LoopProcessWorklist.end(), L);
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if (I != LoopProcessWorklist.end())
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LoopProcessWorklist.erase(I);
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}
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bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L);
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unsigned getLoopUnswitchCost(Loop *L, Value *LIC);
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void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
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BasicBlock *ExitBlock);
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void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
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BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To);
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BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt);
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void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
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Constant *Val, bool isEqual);
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void SimplifyCode(std::vector<Instruction*> &Worklist);
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void RemoveBlockIfDead(BasicBlock *BB,
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std::vector<Instruction*> &Worklist);
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void RemoveLoopFromHierarchy(Loop *L);
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};
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RegisterOpt<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
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}
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FunctionPass *llvm::createLoopUnswitchPass() { return new LoopUnswitch(); }
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bool LoopUnswitch::runOnFunction(Function &F) {
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bool Changed = false;
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LI = &getAnalysis<LoopInfo>();
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// Populate the worklist of loops to process in post-order.
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for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
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for (po_iterator<Loop*> LI = po_begin(*I), E = po_end(*I); LI != E; ++LI)
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LoopProcessWorklist.push_back(*LI);
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// Process the loops in worklist order, this is a post-order visitation of
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// the loops. We use a worklist of loops so that loops can be removed at any
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// time if they are deleted (e.g. the backedge of a loop is removed).
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while (!LoopProcessWorklist.empty()) {
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Loop *L = LoopProcessWorklist.back();
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LoopProcessWorklist.pop_back();
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Changed |= visitLoop(L);
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}
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return Changed;
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}
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/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
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/// invariant in the loop, or has an invariant piece, return the invariant.
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/// Otherwise, return null.
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static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
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// Constants should be folded, not unswitched on!
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if (isa<Constant>(Cond)) return false;
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// TODO: Handle: br (VARIANT|INVARIANT).
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// TODO: Hoist simple expressions out of loops.
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if (L->isLoopInvariant(Cond)) return Cond;
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if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
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if (BO->getOpcode() == Instruction::And ||
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BO->getOpcode() == Instruction::Or) {
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// If either the left or right side is invariant, we can unswitch on this,
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// which will cause the branch to go away in one loop and the condition to
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// simplify in the other one.
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if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
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return LHS;
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if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
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return RHS;
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}
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return 0;
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}
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bool LoopUnswitch::visitLoop(Loop *L) {
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bool Changed = false;
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// Loop over all of the basic blocks in the loop. If we find an interior
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// block that is branching on a loop-invariant condition, we can unswitch this
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// loop.
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for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
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I != E; ++I) {
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TerminatorInst *TI = (*I)->getTerminator();
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if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
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// If this isn't branching on an invariant condition, we can't unswitch
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// it.
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if (BI->isConditional()) {
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// See if this, or some part of it, is loop invariant. If so, we can
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// unswitch on it if we desire.
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Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed);
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if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L)) {
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++NumBranches;
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return true;
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}
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}
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} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
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Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
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if (LoopCond && SI->getNumCases() > 1) {
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// Find a value to unswitch on:
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// FIXME: this should chose the most expensive case!
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Constant *UnswitchVal = SI->getCaseValue(1);
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if (UnswitchIfProfitable(LoopCond, UnswitchVal, L)) {
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++NumSwitches;
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return true;
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}
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}
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}
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// Scan the instructions to check for unswitchable values.
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for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
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BBI != E; ++BBI)
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if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
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Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
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if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L)) {
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++NumSelects;
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return true;
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}
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}
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}
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return Changed;
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}
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/// LoopValuesUsedOutsideLoop - Return true if there are any values defined in
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/// the loop that are used by instructions outside of it.
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static bool LoopValuesUsedOutsideLoop(Loop *L) {
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// We will be doing lots of "loop contains block" queries. Loop::contains is
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// linear time, use a set to speed this up.
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std::set<BasicBlock*> LoopBlocks;
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for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
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BB != E; ++BB)
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LoopBlocks.insert(*BB);
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for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
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BB != E; ++BB) {
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for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I)
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for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
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++UI) {
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BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
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if (!LoopBlocks.count(UserBB))
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return true;
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}
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}
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return false;
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}
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/// isTrivialLoopExitBlock - Check to see if all paths from BB either:
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/// 1. Exit the loop with no side effects.
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/// 2. Branch to the latch block with no side-effects.
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///
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/// If these conditions are true, we return true and set ExitBB to the block we
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/// exit through.
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///
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static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
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BasicBlock *&ExitBB,
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std::set<BasicBlock*> &Visited) {
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if (!Visited.insert(BB).second) {
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// Already visited and Ok, end of recursion.
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return true;
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} else if (!L->contains(BB)) {
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// Otherwise, this is a loop exit, this is fine so long as this is the
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// first exit.
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if (ExitBB != 0) return false;
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ExitBB = BB;
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return true;
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}
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// Otherwise, this is an unvisited intra-loop node. Check all successors.
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for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
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// Check to see if the successor is a trivial loop exit.
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if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
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return false;
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}
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// Okay, everything after this looks good, check to make sure that this block
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// doesn't include any side effects.
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for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
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if (I->mayWriteToMemory())
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return false;
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return true;
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}
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/// isTrivialLoopExitBlock - Return true if the specified block unconditionally
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/// leads to an exit from the specified loop, and has no side-effects in the
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/// process. If so, return the block that is exited to, otherwise return null.
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static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
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std::set<BasicBlock*> Visited;
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Visited.insert(L->getHeader()); // Branches to header are ok.
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BasicBlock *ExitBB = 0;
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if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
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return ExitBB;
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return 0;
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}
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/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
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/// trivial: that is, that the condition controls whether or not the loop does
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/// anything at all. If this is a trivial condition, unswitching produces no
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/// code duplications (equivalently, it produces a simpler loop and a new empty
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/// loop, which gets deleted).
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///
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/// If this is a trivial condition, return true, otherwise return false. When
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/// returning true, this sets Cond and Val to the condition that controls the
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/// trivial condition: when Cond dynamically equals Val, the loop is known to
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/// exit. Finally, this sets LoopExit to the BB that the loop exits to when
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/// Cond == Val.
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///
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static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond, Constant **Val = 0,
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BasicBlock **LoopExit = 0) {
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BasicBlock *Header = L->getHeader();
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TerminatorInst *HeaderTerm = Header->getTerminator();
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BasicBlock *LoopExitBB = 0;
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if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
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// If the header block doesn't end with a conditional branch on Cond, we
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// can't handle it.
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if (!BI->isConditional() || BI->getCondition() != Cond)
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return false;
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// Check to see if a successor of the branch is guaranteed to go to the
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// latch block or exit through a one exit block without having any
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// side-effects. If so, determine the value of Cond that causes it to do
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// this.
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if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(0)))) {
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if (Val) *Val = ConstantBool::True;
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} else if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(1)))) {
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if (Val) *Val = ConstantBool::False;
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}
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} else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
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// If this isn't a switch on Cond, we can't handle it.
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if (SI->getCondition() != Cond) return false;
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// Check to see if a successor of the switch is guaranteed to go to the
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// latch block or exit through a one exit block without having any
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// side-effects. If so, determine the value of Cond that causes it to do
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// this. Note that we can't trivially unswitch on the default case.
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for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
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if ((LoopExitBB = isTrivialLoopExitBlock(L, SI->getSuccessor(i)))) {
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// Okay, we found a trivial case, remember the value that is trivial.
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if (Val) *Val = SI->getCaseValue(i);
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break;
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}
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}
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// If we didn't find a single unique LoopExit block, or if the loop exit block
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// contains phi nodes, this isn't trivial.
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if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
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return false; // Can't handle this.
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if (LoopExit) *LoopExit = LoopExitBB;
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// We already know that nothing uses any scalar values defined inside of this
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// loop. As such, we just have to check to see if this loop will execute any
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// side-effecting instructions (e.g. stores, calls, volatile loads) in the
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// part of the loop that the code *would* execute. We already checked the
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// tail, check the header now.
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for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
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if (I->mayWriteToMemory())
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return false;
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return true;
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}
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/// getLoopUnswitchCost - Return the cost (code size growth) that will happen if
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/// we choose to unswitch the specified loop on the specified value.
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///
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unsigned LoopUnswitch::getLoopUnswitchCost(Loop *L, Value *LIC) {
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// If the condition is trivial, always unswitch. There is no code growth for
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// this case.
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if (IsTrivialUnswitchCondition(L, LIC))
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return 0;
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unsigned Cost = 0;
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// FIXME: this is brain dead. It should take into consideration code
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// shrinkage.
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for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
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I != E; ++I) {
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BasicBlock *BB = *I;
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// Do not include empty blocks in the cost calculation. This happen due to
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// loop canonicalization and will be removed.
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if (BB->begin() == BasicBlock::iterator(BB->getTerminator()))
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continue;
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// Count basic blocks.
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++Cost;
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}
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return Cost;
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}
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/// UnswitchIfProfitable - We have found that we can unswitch L when
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/// LoopCond == Val to simplify the loop. If we decide that this is profitable,
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/// unswitch the loop, reprocess the pieces, then return true.
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bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){
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// Check to see if it would be profitable to unswitch this loop.
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unsigned Cost = getLoopUnswitchCost(L, LoopCond);
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if (Cost > Threshold) {
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// FIXME: this should estimate growth by the amount of code shared by the
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// resultant unswitched loops.
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//
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DEBUG(std::cerr << "NOT unswitching loop %"
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<< L->getHeader()->getName() << ", cost too high: "
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<< L->getBlocks().size() << "\n");
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return false;
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}
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// If this loop has live-out values, we can't unswitch it. We need something
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// like loop-closed SSA form in order to know how to insert PHI nodes for
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// these values.
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if (LoopValuesUsedOutsideLoop(L)) {
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DEBUG(std::cerr << "NOT unswitching loop %" << L->getHeader()->getName()
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<< ", a loop value is used outside loop! Cost: "
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<< Cost << "\n");
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return false;
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}
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// If this is a trivial condition to unswitch (which results in no code
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// duplication), do it now.
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Constant *CondVal;
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BasicBlock *ExitBlock;
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if (IsTrivialUnswitchCondition(L, LoopCond, &CondVal, &ExitBlock)) {
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UnswitchTrivialCondition(L, LoopCond, CondVal, ExitBlock);
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} else {
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UnswitchNontrivialCondition(LoopCond, Val, L);
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}
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return true;
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}
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/// SplitBlock - Split the specified block at the specified instruction - every
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/// thing before SplitPt stays in Old and everything starting with SplitPt moves
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/// to a new block. The two blocks are joined by an unconditional branch and
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/// the loop info is updated.
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///
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BasicBlock *LoopUnswitch::SplitBlock(BasicBlock *Old, Instruction *SplitPt) {
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BasicBlock::iterator SplitIt = SplitPt;
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while (isa<PHINode>(SplitIt))
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++SplitIt;
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BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
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// The new block lives in whichever loop the old one did.
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if (Loop *L = LI->getLoopFor(Old))
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L->addBasicBlockToLoop(New, *LI);
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return New;
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}
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BasicBlock *LoopUnswitch::SplitEdge(BasicBlock *BB, BasicBlock *Succ) {
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TerminatorInst *LatchTerm = BB->getTerminator();
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unsigned SuccNum = 0;
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for (unsigned i = 0, e = LatchTerm->getNumSuccessors(); ; ++i) {
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assert(i != e && "Didn't find edge?");
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if (LatchTerm->getSuccessor(i) == Succ) {
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SuccNum = i;
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break;
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}
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}
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// If this is a critical edge, let SplitCriticalEdge do it.
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if (SplitCriticalEdge(BB->getTerminator(), SuccNum, this))
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return LatchTerm->getSuccessor(SuccNum);
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// If the edge isn't critical, then BB has a single successor or Succ has a
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// single pred. Split the block.
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BasicBlock::iterator SplitPoint;
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if (BasicBlock *SP = Succ->getSinglePredecessor()) {
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// If the successor only has a single pred, split the top of the successor
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// block.
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assert(SP == BB && "CFG broken");
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return SplitBlock(Succ, Succ->begin());
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} else {
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// Otherwise, if BB has a single successor, split it at the bottom of the
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// block.
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assert(BB->getTerminator()->getNumSuccessors() == 1 &&
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"Should have a single succ!");
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return SplitBlock(BB, BB->getTerminator());
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}
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}
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|
|
// RemapInstruction - Convert the instruction operands from referencing the
|
|
// current values into those specified by ValueMap.
|
|
//
|
|
static inline void RemapInstruction(Instruction *I,
|
|
std::map<const Value *, Value*> &ValueMap) {
|
|
for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
|
|
Value *Op = I->getOperand(op);
|
|
std::map<const Value *, Value*>::iterator It = ValueMap.find(Op);
|
|
if (It != ValueMap.end()) Op = It->second;
|
|
I->setOperand(op, Op);
|
|
}
|
|
}
|
|
|
|
/// CloneLoop - Recursively clone the specified loop and all of its children,
|
|
/// mapping the blocks with the specified map.
|
|
static Loop *CloneLoop(Loop *L, Loop *PL, std::map<const Value*, Value*> &VM,
|
|
LoopInfo *LI) {
|
|
Loop *New = new Loop();
|
|
|
|
if (PL)
|
|
PL->addChildLoop(New);
|
|
else
|
|
LI->addTopLevelLoop(New);
|
|
|
|
// Add all of the blocks in L to the new loop.
|
|
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
|
|
I != E; ++I)
|
|
if (LI->getLoopFor(*I) == L)
|
|
New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);
|
|
|
|
// Add all of the subloops to the new loop.
|
|
for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
|
|
CloneLoop(*I, New, VM, LI);
|
|
|
|
return New;
|
|
}
|
|
|
|
/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
|
|
/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
|
|
/// code immediately before InsertPt.
|
|
static void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
|
|
BasicBlock *TrueDest,
|
|
BasicBlock *FalseDest,
|
|
Instruction *InsertPt) {
|
|
// Insert a conditional branch on LIC to the two preheaders. The original
|
|
// code is the true version and the new code is the false version.
|
|
Value *BranchVal = LIC;
|
|
if (!isa<ConstantBool>(Val)) {
|
|
BranchVal = BinaryOperator::createSetEQ(LIC, Val, "tmp", InsertPt);
|
|
} else if (Val != ConstantBool::True) {
|
|
// We want to enter the new loop when the condition is true.
|
|
std::swap(TrueDest, FalseDest);
|
|
}
|
|
|
|
// Insert the new branch.
|
|
new BranchInst(TrueDest, FalseDest, BranchVal, InsertPt);
|
|
}
|
|
|
|
|
|
/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
|
|
/// condition in it (a cond branch from its header block to its latch block,
|
|
/// where the path through the loop that doesn't execute its body has no
|
|
/// side-effects), unswitch it. This doesn't involve any code duplication, just
|
|
/// moving the conditional branch outside of the loop and updating loop info.
|
|
void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
|
|
Constant *Val,
|
|
BasicBlock *ExitBlock) {
|
|
DEBUG(std::cerr << "loop-unswitch: Trivial-Unswitch loop %"
|
|
<< L->getHeader()->getName() << " [" << L->getBlocks().size()
|
|
<< " blocks] in Function " << L->getHeader()->getParent()->getName()
|
|
<< " on cond: " << *Val << " == " << *Cond << "\n");
|
|
|
|
// First step, split the preheader, so that we know that there is a safe place
|
|
// to insert the conditional branch. We will change 'OrigPH' to have a
|
|
// conditional branch on Cond.
|
|
BasicBlock *OrigPH = L->getLoopPreheader();
|
|
BasicBlock *NewPH = SplitEdge(OrigPH, L->getHeader());
|
|
|
|
// Now that we have a place to insert the conditional branch, create a place
|
|
// to branch to: this is the exit block out of the loop that we should
|
|
// short-circuit to.
|
|
|
|
// Split this block now, so that the loop maintains its exit block, and so
|
|
// that the jump from the preheader can execute the contents of the exit block
|
|
// without actually branching to it (the exit block should be dominated by the
|
|
// loop header, not the preheader).
|
|
assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
|
|
BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin());
|
|
|
|
// Okay, now we have a position to branch from and a position to branch to,
|
|
// insert the new conditional branch.
|
|
EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
|
|
OrigPH->getTerminator());
|
|
OrigPH->getTerminator()->eraseFromParent();
|
|
|
|
// We need to reprocess this loop, it could be unswitched again.
|
|
LoopProcessWorklist.push_back(L);
|
|
|
|
// Now that we know that the loop is never entered when this condition is a
|
|
// particular value, rewrite the loop with this info. We know that this will
|
|
// at least eliminate the old branch.
|
|
RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
|
|
++NumTrivial;
|
|
}
|
|
|
|
|
|
/// VersionLoop - We determined that the loop is profitable to unswitch when LIC
|
|
/// equal Val. Split it into loop versions and test the condition outside of
|
|
/// either loop. Return the loops created as Out1/Out2.
|
|
void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
|
|
Loop *L) {
|
|
Function *F = L->getHeader()->getParent();
|
|
DEBUG(std::cerr << "loop-unswitch: Unswitching loop %"
|
|
<< L->getHeader()->getName() << " [" << L->getBlocks().size()
|
|
<< " blocks] in Function " << F->getName()
|
|
<< " when '" << *Val << "' == " << *LIC << "\n");
|
|
|
|
// LoopBlocks contains all of the basic blocks of the loop, including the
|
|
// preheader of the loop, the body of the loop, and the exit blocks of the
|
|
// loop, in that order.
|
|
std::vector<BasicBlock*> LoopBlocks;
|
|
|
|
// First step, split the preheader and exit blocks, and add these blocks to
|
|
// the LoopBlocks list.
|
|
BasicBlock *OrigPreheader = L->getLoopPreheader();
|
|
LoopBlocks.push_back(SplitEdge(OrigPreheader, L->getHeader()));
|
|
|
|
// We want the loop to come after the preheader, but before the exit blocks.
|
|
LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
|
|
|
|
std::vector<BasicBlock*> ExitBlocks;
|
|
L->getExitBlocks(ExitBlocks);
|
|
std::sort(ExitBlocks.begin(), ExitBlocks.end());
|
|
ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
|
|
ExitBlocks.end());
|
|
|
|
// Split all of the edges from inside the loop to their exit blocks. This
|
|
// unswitching trivial: no phi nodes to update.
|
|
unsigned NumBlocks = L->getBlocks().size();
|
|
|
|
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
|
|
BasicBlock *ExitBlock = ExitBlocks[i];
|
|
std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock));
|
|
|
|
for (unsigned j = 0, e = Preds.size(); j != e; ++j) {
|
|
assert(L->contains(Preds[j]) &&
|
|
"All preds of loop exit blocks must be the same loop!");
|
|
SplitEdge(Preds[j], ExitBlock);
|
|
}
|
|
}
|
|
|
|
// The exit blocks may have been changed due to edge splitting, recompute.
|
|
ExitBlocks.clear();
|
|
L->getExitBlocks(ExitBlocks);
|
|
std::sort(ExitBlocks.begin(), ExitBlocks.end());
|
|
ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
|
|
ExitBlocks.end());
|
|
|
|
// Add exit blocks to the loop blocks.
|
|
LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
|
|
|
|
// Next step, clone all of the basic blocks that make up the loop (including
|
|
// the loop preheader and exit blocks), keeping track of the mapping between
|
|
// the instructions and blocks.
|
|
std::vector<BasicBlock*> NewBlocks;
|
|
NewBlocks.reserve(LoopBlocks.size());
|
|
std::map<const Value*, Value*> ValueMap;
|
|
for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
|
|
BasicBlock *New = CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F);
|
|
NewBlocks.push_back(New);
|
|
ValueMap[LoopBlocks[i]] = New; // Keep the BB mapping.
|
|
}
|
|
|
|
// Splice the newly inserted blocks into the function right before the
|
|
// original preheader.
|
|
F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(),
|
|
NewBlocks[0], F->end());
|
|
|
|
// Now we create the new Loop object for the versioned loop.
|
|
Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI);
|
|
Loop *ParentLoop = L->getParentLoop();
|
|
if (ParentLoop) {
|
|
// Make sure to add the cloned preheader and exit blocks to the parent loop
|
|
// as well.
|
|
ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI);
|
|
}
|
|
|
|
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
|
|
BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]);
|
|
// The new exit block should be in the same loop as the old one.
|
|
if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
|
|
ExitBBLoop->addBasicBlockToLoop(NewExit, *LI);
|
|
|
|
assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
|
|
"Exit block should have been split to have one successor!");
|
|
BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
|
|
|
|
// If the successor of the exit block had PHI nodes, add an entry for
|
|
// NewExit.
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator I = ExitSucc->begin();
|
|
(PN = dyn_cast<PHINode>(I)); ++I) {
|
|
Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
|
|
std::map<const Value *, Value*>::iterator It = ValueMap.find(V);
|
|
if (It != ValueMap.end()) V = It->second;
|
|
PN->addIncoming(V, NewExit);
|
|
}
|
|
}
|
|
|
|
// Rewrite the code to refer to itself.
|
|
for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
|
|
for (BasicBlock::iterator I = NewBlocks[i]->begin(),
|
|
E = NewBlocks[i]->end(); I != E; ++I)
|
|
RemapInstruction(I, ValueMap);
|
|
|
|
// Rewrite the original preheader to select between versions of the loop.
|
|
BranchInst *OldBR = cast<BranchInst>(OrigPreheader->getTerminator());
|
|
assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
|
|
"Preheader splitting did not work correctly!");
|
|
|
|
// Emit the new branch that selects between the two versions of this loop.
|
|
EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
|
|
OldBR->eraseFromParent();
|
|
|
|
LoopProcessWorklist.push_back(L);
|
|
LoopProcessWorklist.push_back(NewLoop);
|
|
|
|
// Now we rewrite the original code to know that the condition is true and the
|
|
// new code to know that the condition is false.
|
|
RewriteLoopBodyWithConditionConstant(L , LIC, Val, false);
|
|
|
|
// It's possible that simplifying one loop could cause the other to be
|
|
// deleted. If so, don't simplify it.
|
|
if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop)
|
|
RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true);
|
|
}
|
|
|
|
/// RemoveFromWorklist - Remove all instances of I from the worklist vector
|
|
/// specified.
|
|
static void RemoveFromWorklist(Instruction *I,
|
|
std::vector<Instruction*> &Worklist) {
|
|
std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
|
|
Worklist.end(), I);
|
|
while (WI != Worklist.end()) {
|
|
unsigned Offset = WI-Worklist.begin();
|
|
Worklist.erase(WI);
|
|
WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
|
|
}
|
|
}
|
|
|
|
/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
|
|
/// program, replacing all uses with V and update the worklist.
|
|
static void ReplaceUsesOfWith(Instruction *I, Value *V,
|
|
std::vector<Instruction*> &Worklist) {
|
|
DEBUG(std::cerr << "Replace with '" << *V << "': " << *I);
|
|
|
|
// Add uses to the worklist, which may be dead now.
|
|
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
|
|
if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
|
|
Worklist.push_back(Use);
|
|
|
|
// Add users to the worklist which may be simplified now.
|
|
for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
|
|
UI != E; ++UI)
|
|
Worklist.push_back(cast<Instruction>(*UI));
|
|
I->replaceAllUsesWith(V);
|
|
I->eraseFromParent();
|
|
RemoveFromWorklist(I, Worklist);
|
|
++NumSimplify;
|
|
}
|
|
|
|
/// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
|
|
/// information, and remove any dead successors it has.
|
|
///
|
|
void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
|
|
std::vector<Instruction*> &Worklist) {
|
|
if (pred_begin(BB) != pred_end(BB)) {
|
|
// This block isn't dead, since an edge to BB was just removed, see if there
|
|
// are any easy simplifications we can do now.
|
|
if (BasicBlock *Pred = BB->getSinglePredecessor()) {
|
|
// If it has one pred, fold phi nodes in BB.
|
|
while (isa<PHINode>(BB->begin()))
|
|
ReplaceUsesOfWith(BB->begin(),
|
|
cast<PHINode>(BB->begin())->getIncomingValue(0),
|
|
Worklist);
|
|
|
|
// If this is the header of a loop and the only pred is the latch, we now
|
|
// have an unreachable loop.
|
|
if (Loop *L = LI->getLoopFor(BB))
|
|
if (L->getHeader() == BB && L->contains(Pred)) {
|
|
// Remove the branch from the latch to the header block, this makes
|
|
// the header dead, which will make the latch dead (because the header
|
|
// dominates the latch).
|
|
Pred->getTerminator()->eraseFromParent();
|
|
new UnreachableInst(Pred);
|
|
|
|
// The loop is now broken, remove it from LI.
|
|
RemoveLoopFromHierarchy(L);
|
|
|
|
// Reprocess the header, which now IS dead.
|
|
RemoveBlockIfDead(BB, Worklist);
|
|
return;
|
|
}
|
|
|
|
// If pred ends in a uncond branch, add uncond branch to worklist so that
|
|
// the two blocks will get merged.
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
|
|
if (BI->isUnconditional())
|
|
Worklist.push_back(BI);
|
|
}
|
|
return;
|
|
}
|
|
|
|
DEBUG(std::cerr << "Nuking dead block: " << *BB);
|
|
|
|
// Remove the instructions in the basic block from the worklist.
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
|
|
RemoveFromWorklist(I, Worklist);
|
|
|
|
// Anything that uses the instructions in this basic block should have their
|
|
// uses replaced with undefs.
|
|
if (!I->use_empty())
|
|
I->replaceAllUsesWith(UndefValue::get(I->getType()));
|
|
}
|
|
|
|
// If this is the edge to the header block for a loop, remove the loop and
|
|
// promote all subloops.
|
|
if (Loop *BBLoop = LI->getLoopFor(BB)) {
|
|
if (BBLoop->getLoopLatch() == BB)
|
|
RemoveLoopFromHierarchy(BBLoop);
|
|
}
|
|
|
|
// Remove the block from the loop info, which removes it from any loops it
|
|
// was in.
|
|
LI->removeBlock(BB);
|
|
|
|
|
|
// Remove phi node entries in successors for this block.
|
|
TerminatorInst *TI = BB->getTerminator();
|
|
std::vector<BasicBlock*> Succs;
|
|
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
|
|
Succs.push_back(TI->getSuccessor(i));
|
|
TI->getSuccessor(i)->removePredecessor(BB);
|
|
}
|
|
|
|
// Unique the successors, remove anything with multiple uses.
|
|
std::sort(Succs.begin(), Succs.end());
|
|
Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
|
|
|
|
// Remove the basic block, including all of the instructions contained in it.
|
|
BB->eraseFromParent();
|
|
|
|
// Remove successor blocks here that are not dead, so that we know we only
|
|
// have dead blocks in this list. Nondead blocks have a way of becoming dead,
|
|
// then getting removed before we revisit them, which is badness.
|
|
//
|
|
for (unsigned i = 0; i != Succs.size(); ++i)
|
|
if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
|
|
// One exception is loop headers. If this block was the preheader for a
|
|
// loop, then we DO want to visit the loop so the loop gets deleted.
|
|
// We know that if the successor is a loop header, that this loop had to
|
|
// be the preheader: the case where this was the latch block was handled
|
|
// above and headers can only have two predecessors.
|
|
if (!LI->isLoopHeader(Succs[i])) {
|
|
Succs.erase(Succs.begin()+i);
|
|
--i;
|
|
}
|
|
}
|
|
|
|
for (unsigned i = 0, e = Succs.size(); i != e; ++i)
|
|
RemoveBlockIfDead(Succs[i], Worklist);
|
|
}
|
|
|
|
/// RemoveLoopFromHierarchy - We have discovered that the specified loop has
|
|
/// become unwrapped, either because the backedge was deleted, or because the
|
|
/// edge into the header was removed. If the edge into the header from the
|
|
/// latch block was removed, the loop is unwrapped but subloops are still alive,
|
|
/// so they just reparent loops. If the loops are actually dead, they will be
|
|
/// removed later.
|
|
void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) {
|
|
if (Loop *ParentLoop = L->getParentLoop()) { // Not a top-level loop.
|
|
// Reparent all of the blocks in this loop. Since BBLoop had a parent,
|
|
// they are now all in it.
|
|
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
|
|
I != E; ++I)
|
|
if (LI->getLoopFor(*I) == L) // Don't change blocks in subloops.
|
|
LI->changeLoopFor(*I, ParentLoop);
|
|
|
|
// Remove the loop from its parent loop.
|
|
for (Loop::iterator I = ParentLoop->begin(), E = ParentLoop->end();;
|
|
++I) {
|
|
assert(I != E && "Couldn't find loop");
|
|
if (*I == L) {
|
|
ParentLoop->removeChildLoop(I);
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Move all subloops into the parent loop.
|
|
while (L->begin() != L->end())
|
|
ParentLoop->addChildLoop(L->removeChildLoop(L->end()-1));
|
|
} else {
|
|
// Reparent all of the blocks in this loop. Since BBLoop had no parent,
|
|
// they no longer in a loop at all.
|
|
|
|
for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
|
|
// Don't change blocks in subloops.
|
|
if (LI->getLoopFor(L->getBlocks()[i]) == L) {
|
|
LI->removeBlock(L->getBlocks()[i]);
|
|
--i;
|
|
}
|
|
}
|
|
|
|
// Remove the loop from the top-level LoopInfo object.
|
|
for (LoopInfo::iterator I = LI->begin(), E = LI->end();; ++I) {
|
|
assert(I != E && "Couldn't find loop");
|
|
if (*I == L) {
|
|
LI->removeLoop(I);
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Move all of the subloops to the top-level.
|
|
while (L->begin() != L->end())
|
|
LI->addTopLevelLoop(L->removeChildLoop(L->end()-1));
|
|
}
|
|
|
|
delete L;
|
|
RemoveLoopFromWorklist(L);
|
|
}
|
|
|
|
|
|
|
|
// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
|
|
// the value specified by Val in the specified loop, or we know it does NOT have
|
|
// that value. Rewrite any uses of LIC or of properties correlated to it.
|
|
void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
|
|
Constant *Val,
|
|
bool IsEqual) {
|
|
assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
|
|
|
|
// FIXME: Support correlated properties, like:
|
|
// for (...)
|
|
// if (li1 < li2)
|
|
// ...
|
|
// if (li1 > li2)
|
|
// ...
|
|
|
|
// FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
|
|
// selects, switches.
|
|
std::vector<User*> Users(LIC->use_begin(), LIC->use_end());
|
|
std::vector<Instruction*> Worklist;
|
|
|
|
// If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
|
|
// in the loop with the appropriate one directly.
|
|
if (IsEqual || isa<ConstantBool>(Val)) {
|
|
Value *Replacement;
|
|
if (IsEqual)
|
|
Replacement = Val;
|
|
else
|
|
Replacement = ConstantBool::get(!cast<ConstantBool>(Val)->getValue());
|
|
|
|
for (unsigned i = 0, e = Users.size(); i != e; ++i)
|
|
if (Instruction *U = cast<Instruction>(Users[i])) {
|
|
if (!L->contains(U->getParent()))
|
|
continue;
|
|
U->replaceUsesOfWith(LIC, Replacement);
|
|
Worklist.push_back(U);
|
|
}
|
|
} else {
|
|
// Otherwise, we don't know the precise value of LIC, but we do know that it
|
|
// is certainly NOT "Val". As such, simplify any uses in the loop that we
|
|
// can. This case occurs when we unswitch switch statements.
|
|
for (unsigned i = 0, e = Users.size(); i != e; ++i)
|
|
if (Instruction *U = cast<Instruction>(Users[i])) {
|
|
if (!L->contains(U->getParent()))
|
|
continue;
|
|
|
|
Worklist.push_back(U);
|
|
|
|
// If we know that LIC is not Val, use this info to simplify code.
|
|
if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) {
|
|
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
|
|
if (SI->getCaseValue(i) == Val) {
|
|
// Found a dead case value. Don't remove PHI nodes in the
|
|
// successor if they become single-entry, those PHI nodes may
|
|
// be in the Users list.
|
|
SI->getSuccessor(i)->removePredecessor(SI->getParent(), true);
|
|
SI->removeCase(i);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// TODO: We could do other simplifications, for example, turning
|
|
// LIC == Val -> false.
|
|
}
|
|
}
|
|
|
|
SimplifyCode(Worklist);
|
|
}
|
|
|
|
/// SimplifyCode - Okay, now that we have simplified some instructions in the
|
|
/// loop, walk over it and constant prop, dce, and fold control flow where
|
|
/// possible. Note that this is effectively a very simple loop-structure-aware
|
|
/// optimizer. During processing of this loop, L could very well be deleted, so
|
|
/// it must not be used.
|
|
///
|
|
/// FIXME: When the loop optimizer is more mature, separate this out to a new
|
|
/// pass.
|
|
///
|
|
void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist) {
|
|
while (!Worklist.empty()) {
|
|
Instruction *I = Worklist.back();
|
|
Worklist.pop_back();
|
|
|
|
// Simple constant folding.
|
|
if (Constant *C = ConstantFoldInstruction(I)) {
|
|
ReplaceUsesOfWith(I, C, Worklist);
|
|
continue;
|
|
}
|
|
|
|
// Simple DCE.
|
|
if (isInstructionTriviallyDead(I)) {
|
|
DEBUG(std::cerr << "Remove dead instruction '" << *I);
|
|
|
|
// Add uses to the worklist, which may be dead now.
|
|
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
|
|
if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
|
|
Worklist.push_back(Use);
|
|
I->eraseFromParent();
|
|
RemoveFromWorklist(I, Worklist);
|
|
++NumSimplify;
|
|
continue;
|
|
}
|
|
|
|
// Special case hacks that appear commonly in unswitched code.
|
|
switch (I->getOpcode()) {
|
|
case Instruction::Select:
|
|
if (ConstantBool *CB = dyn_cast<ConstantBool>(I->getOperand(0))) {
|
|
ReplaceUsesOfWith(I, I->getOperand(!CB->getValue()+1), Worklist);
|
|
continue;
|
|
}
|
|
break;
|
|
case Instruction::And:
|
|
if (isa<ConstantBool>(I->getOperand(0))) // constant -> RHS
|
|
cast<BinaryOperator>(I)->swapOperands();
|
|
if (ConstantBool *CB = dyn_cast<ConstantBool>(I->getOperand(1))) {
|
|
if (CB->getValue()) // X & 1 -> X
|
|
ReplaceUsesOfWith(I, I->getOperand(0), Worklist);
|
|
else // X & 0 -> 0
|
|
ReplaceUsesOfWith(I, I->getOperand(1), Worklist);
|
|
continue;
|
|
}
|
|
break;
|
|
case Instruction::Or:
|
|
if (isa<ConstantBool>(I->getOperand(0))) // constant -> RHS
|
|
cast<BinaryOperator>(I)->swapOperands();
|
|
if (ConstantBool *CB = dyn_cast<ConstantBool>(I->getOperand(1))) {
|
|
if (CB->getValue()) // X | 1 -> 1
|
|
ReplaceUsesOfWith(I, I->getOperand(1), Worklist);
|
|
else // X | 0 -> X
|
|
ReplaceUsesOfWith(I, I->getOperand(0), Worklist);
|
|
continue;
|
|
}
|
|
break;
|
|
case Instruction::Br: {
|
|
BranchInst *BI = cast<BranchInst>(I);
|
|
if (BI->isUnconditional()) {
|
|
// If BI's parent is the only pred of the successor, fold the two blocks
|
|
// together.
|
|
BasicBlock *Pred = BI->getParent();
|
|
BasicBlock *Succ = BI->getSuccessor(0);
|
|
BasicBlock *SinglePred = Succ->getSinglePredecessor();
|
|
if (!SinglePred) continue; // Nothing to do.
|
|
assert(SinglePred == Pred && "CFG broken");
|
|
|
|
DEBUG(std::cerr << "Merging blocks: " << Pred->getName() << " <- "
|
|
<< Succ->getName() << "\n");
|
|
|
|
// Resolve any single entry PHI nodes in Succ.
|
|
while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
|
|
ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist);
|
|
|
|
// Move all of the successor contents from Succ to Pred.
|
|
Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
|
|
Succ->end());
|
|
BI->eraseFromParent();
|
|
RemoveFromWorklist(BI, Worklist);
|
|
|
|
// If Succ has any successors with PHI nodes, update them to have
|
|
// entries coming from Pred instead of Succ.
|
|
Succ->replaceAllUsesWith(Pred);
|
|
|
|
// Remove Succ from the loop tree.
|
|
LI->removeBlock(Succ);
|
|
Succ->eraseFromParent();
|
|
++NumSimplify;
|
|
} else if (ConstantBool *CB = dyn_cast<ConstantBool>(BI->getCondition())){
|
|
// Conditional branch. Turn it into an unconditional branch, then
|
|
// remove dead blocks.
|
|
break; // FIXME: Enable.
|
|
|
|
DEBUG(std::cerr << "Folded branch: " << *BI);
|
|
BasicBlock *DeadSucc = BI->getSuccessor(CB->getValue());
|
|
BasicBlock *LiveSucc = BI->getSuccessor(!CB->getValue());
|
|
DeadSucc->removePredecessor(BI->getParent(), true);
|
|
Worklist.push_back(new BranchInst(LiveSucc, BI));
|
|
BI->eraseFromParent();
|
|
RemoveFromWorklist(BI, Worklist);
|
|
++NumSimplify;
|
|
|
|
RemoveBlockIfDead(DeadSucc, Worklist);
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|