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8c7e769325
For code like this: void foo(float *a, float *b, int n, int stride_a, int stride_b) { int i; for (i=0; i<n; i++) a[i*stride_a] = b[i*stride_b]; } we now emit: .LBB_foo2_2: ; no_exit lfs f0, 0(r4) stfs f0, 0(r3) addi r7, r7, 1 add r4, r2, r4 add r3, r6, r3 cmpw cr0, r7, r5 blt .LBB_foo2_2 ; no_exit instead of: .LBB_foo_2: ; no_exit mullw r8, r2, r7 ;; multiply! slwi r8, r8, 2 lfsx f0, r4, r8 mullw r8, r2, r6 ;; multiply! slwi r8, r8, 2 stfsx f0, r3, r8 addi r2, r2, 1 cmpw cr0, r2, r5 blt .LBB_foo_2 ; no_exit loops with variable strides occur pretty often. For example, in SPECFP2K there are 317 variable strides in 177.mesa, 3 in 179.art, 14 in 188.ammp, 56 in 168.wupwise, 36 in 172.mgrid. Now we can allow indvars to turn functions written like this: void foo2(float *a, float *b, int n, int stride_a, int stride_b) { int i, ai = 0, bi = 0; for (i=0; i<n; i++) { a[ai] = b[bi]; ai += stride_a; bi += stride_b; } } into code like the above for better analysis. With this patch, they generate identical code. llvm-svn: 22740
955 lines
38 KiB
C++
955 lines
38 KiB
C++
//===- LoopStrengthReduce.cpp - Strength Reduce GEPs in Loops -------------===//
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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 Nate Begeman and is distributed under the
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// 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 performs a strength reduction on array references inside loops that
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// have as one or more of their components the loop induction variable. This is
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// accomplished by creating a new Value to hold the initial value of the array
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// access for the first iteration, and then creating a new GEP instruction in
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// the loop to increment the value by the appropriate amount.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "loop-reduce"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/Type.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/ScalarEvolutionExpander.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Support/Debug.h"
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#include <algorithm>
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#include <set>
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using namespace llvm;
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namespace {
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Statistic<> NumReduced ("loop-reduce", "Number of GEPs strength reduced");
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Statistic<> NumInserted("loop-reduce", "Number of PHIs inserted");
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Statistic<> NumVariable("loop-reduce","Number of PHIs with variable strides");
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/// IVStrideUse - Keep track of one use of a strided induction variable, where
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/// the stride is stored externally. The Offset member keeps track of the
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/// offset from the IV, User is the actual user of the operand, and 'Operand'
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/// is the operand # of the User that is the use.
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struct IVStrideUse {
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SCEVHandle Offset;
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Instruction *User;
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Value *OperandValToReplace;
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// isUseOfPostIncrementedValue - True if this should use the
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// post-incremented version of this IV, not the preincremented version.
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// This can only be set in special cases, such as the terminating setcc
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// instruction for a loop.
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bool isUseOfPostIncrementedValue;
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IVStrideUse(const SCEVHandle &Offs, Instruction *U, Value *O)
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: Offset(Offs), User(U), OperandValToReplace(O),
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isUseOfPostIncrementedValue(false) {}
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};
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/// IVUsersOfOneStride - This structure keeps track of all instructions that
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/// have an operand that is based on the trip count multiplied by some stride.
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/// The stride for all of these users is common and kept external to this
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/// structure.
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struct IVUsersOfOneStride {
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/// Users - Keep track of all of the users of this stride as well as the
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/// initial value and the operand that uses the IV.
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std::vector<IVStrideUse> Users;
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void addUser(const SCEVHandle &Offset,Instruction *User, Value *Operand) {
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Users.push_back(IVStrideUse(Offset, User, Operand));
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}
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};
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class LoopStrengthReduce : public FunctionPass {
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LoopInfo *LI;
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DominatorSet *DS;
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ScalarEvolution *SE;
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const TargetData *TD;
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const Type *UIntPtrTy;
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bool Changed;
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/// MaxTargetAMSize - This is the maximum power-of-two scale value that the
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/// target can handle for free with its addressing modes.
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unsigned MaxTargetAMSize;
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/// IVUsesByStride - Keep track of all uses of induction variables that we
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/// are interested in. The key of the map is the stride of the access.
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std::map<SCEVHandle, IVUsersOfOneStride> IVUsesByStride;
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/// CastedValues - As we need to cast values to uintptr_t, this keeps track
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/// of the casted version of each value. This is accessed by
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/// getCastedVersionOf.
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std::map<Value*, Value*> CastedPointers;
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/// DeadInsts - Keep track of instructions we may have made dead, so that
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/// we can remove them after we are done working.
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std::set<Instruction*> DeadInsts;
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public:
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LoopStrengthReduce(unsigned MTAMS = 1)
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: MaxTargetAMSize(MTAMS) {
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}
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virtual bool runOnFunction(Function &) {
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LI = &getAnalysis<LoopInfo>();
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DS = &getAnalysis<DominatorSet>();
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SE = &getAnalysis<ScalarEvolution>();
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TD = &getAnalysis<TargetData>();
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UIntPtrTy = TD->getIntPtrType();
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Changed = false;
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for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
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runOnLoop(*I);
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return Changed;
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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AU.addRequiredID(LoopSimplifyID);
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AU.addRequired<LoopInfo>();
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AU.addRequired<DominatorSet>();
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AU.addRequired<TargetData>();
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AU.addRequired<ScalarEvolution>();
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}
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/// getCastedVersionOf - Return the specified value casted to uintptr_t.
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///
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Value *getCastedVersionOf(Value *V);
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private:
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void runOnLoop(Loop *L);
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bool AddUsersIfInteresting(Instruction *I, Loop *L,
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std::set<Instruction*> &Processed);
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SCEVHandle GetExpressionSCEV(Instruction *E, Loop *L);
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void OptimizeIndvars(Loop *L);
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void StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
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IVUsersOfOneStride &Uses,
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Loop *L, bool isOnlyStride);
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void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts);
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};
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RegisterOpt<LoopStrengthReduce> X("loop-reduce",
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"Strength Reduce GEP Uses of Ind. Vars");
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}
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FunctionPass *llvm::createLoopStrengthReducePass(unsigned MaxTargetAMSize) {
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return new LoopStrengthReduce(MaxTargetAMSize);
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}
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/// getCastedVersionOf - Return the specified value casted to uintptr_t.
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///
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Value *LoopStrengthReduce::getCastedVersionOf(Value *V) {
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if (V->getType() == UIntPtrTy) return V;
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if (Constant *CB = dyn_cast<Constant>(V))
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return ConstantExpr::getCast(CB, UIntPtrTy);
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Value *&New = CastedPointers[V];
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if (New) return New;
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BasicBlock::iterator InsertPt;
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if (Argument *Arg = dyn_cast<Argument>(V)) {
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// Insert into the entry of the function, after any allocas.
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InsertPt = Arg->getParent()->begin()->begin();
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while (isa<AllocaInst>(InsertPt)) ++InsertPt;
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} else {
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if (InvokeInst *II = dyn_cast<InvokeInst>(V)) {
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InsertPt = II->getNormalDest()->begin();
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} else {
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InsertPt = cast<Instruction>(V);
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++InsertPt;
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}
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// Do not insert casts into the middle of PHI node blocks.
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while (isa<PHINode>(InsertPt)) ++InsertPt;
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}
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New = new CastInst(V, UIntPtrTy, V->getName(), InsertPt);
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DeadInsts.insert(cast<Instruction>(New));
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return New;
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}
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/// DeleteTriviallyDeadInstructions - If any of the instructions is the
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/// specified set are trivially dead, delete them and see if this makes any of
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/// their operands subsequently dead.
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void LoopStrengthReduce::
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DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) {
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while (!Insts.empty()) {
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Instruction *I = *Insts.begin();
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Insts.erase(Insts.begin());
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if (isInstructionTriviallyDead(I)) {
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
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if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i)))
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Insts.insert(U);
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SE->deleteInstructionFromRecords(I);
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I->eraseFromParent();
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Changed = true;
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}
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}
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}
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/// GetExpressionSCEV - Compute and return the SCEV for the specified
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/// instruction.
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SCEVHandle LoopStrengthReduce::GetExpressionSCEV(Instruction *Exp, Loop *L) {
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// Scalar Evolutions doesn't know how to compute SCEV's for GEP instructions.
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// If this is a GEP that SE doesn't know about, compute it now and insert it.
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// If this is not a GEP, or if we have already done this computation, just let
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// SE figure it out.
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GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Exp);
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if (!GEP || SE->hasSCEV(GEP))
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return SE->getSCEV(Exp);
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// Analyze all of the subscripts of this getelementptr instruction, looking
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// for uses that are determined by the trip count of L. First, skip all
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// operands the are not dependent on the IV.
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// Build up the base expression. Insert an LLVM cast of the pointer to
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// uintptr_t first.
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SCEVHandle GEPVal = SCEVUnknown::get(getCastedVersionOf(GEP->getOperand(0)));
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gep_type_iterator GTI = gep_type_begin(GEP);
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for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
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// If this is a use of a recurrence that we can analyze, and it comes before
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// Op does in the GEP operand list, we will handle this when we process this
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// operand.
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if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
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const StructLayout *SL = TD->getStructLayout(STy);
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unsigned Idx = cast<ConstantUInt>(GEP->getOperand(i))->getValue();
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uint64_t Offset = SL->MemberOffsets[Idx];
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GEPVal = SCEVAddExpr::get(GEPVal,
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SCEVUnknown::getIntegerSCEV(Offset, UIntPtrTy));
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} else {
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Value *OpVal = getCastedVersionOf(GEP->getOperand(i));
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SCEVHandle Idx = SE->getSCEV(OpVal);
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uint64_t TypeSize = TD->getTypeSize(GTI.getIndexedType());
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if (TypeSize != 1)
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Idx = SCEVMulExpr::get(Idx,
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SCEVConstant::get(ConstantUInt::get(UIntPtrTy,
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TypeSize)));
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GEPVal = SCEVAddExpr::get(GEPVal, Idx);
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}
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}
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SE->setSCEV(GEP, GEPVal);
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return GEPVal;
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}
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/// getSCEVStartAndStride - Compute the start and stride of this expression,
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/// returning false if the expression is not a start/stride pair, or true if it
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/// is. The stride must be a loop invariant expression, but the start may be
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/// a mix of loop invariant and loop variant expressions.
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static bool getSCEVStartAndStride(const SCEVHandle &SH, Loop *L,
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SCEVHandle &Start, SCEVHandle &Stride) {
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SCEVHandle TheAddRec = Start; // Initialize to zero.
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// If the outer level is an AddExpr, the operands are all start values except
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// for a nested AddRecExpr.
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if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(SH)) {
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for (unsigned i = 0, e = AE->getNumOperands(); i != e; ++i)
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if (SCEVAddRecExpr *AddRec =
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dyn_cast<SCEVAddRecExpr>(AE->getOperand(i))) {
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if (AddRec->getLoop() == L)
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TheAddRec = SCEVAddExpr::get(AddRec, TheAddRec);
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else
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return false; // Nested IV of some sort?
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} else {
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Start = SCEVAddExpr::get(Start, AE->getOperand(i));
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}
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} else if (SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SH)) {
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TheAddRec = SH;
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} else {
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return false; // not analyzable.
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}
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SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(TheAddRec);
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if (!AddRec || AddRec->getLoop() != L) return false;
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// FIXME: Generalize to non-affine IV's.
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if (!AddRec->isAffine()) return false;
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Start = SCEVAddExpr::get(Start, AddRec->getOperand(0));
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if (!isa<SCEVConstant>(AddRec->getOperand(1)))
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DEBUG(std::cerr << "[" << L->getHeader()->getName()
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<< "] Variable stride: " << *AddRec << "\n");
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Stride = AddRec->getOperand(1);
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// Check that all constant strides are the unsigned type, we don't want to
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// have two IV's one of signed stride 4 and one of unsigned stride 4 to not be
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// merged.
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assert((!isa<SCEVConstant>(Stride) || Stride->getType()->isUnsigned()) &&
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"Constants should be canonicalized to unsigned!");
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return true;
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}
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/// AddUsersIfInteresting - Inspect the specified instruction. If it is a
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/// reducible SCEV, recursively add its users to the IVUsesByStride set and
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/// return true. Otherwise, return false.
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bool LoopStrengthReduce::AddUsersIfInteresting(Instruction *I, Loop *L,
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std::set<Instruction*> &Processed) {
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if (I->getType() == Type::VoidTy) return false;
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if (!Processed.insert(I).second)
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return true; // Instruction already handled.
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// Get the symbolic expression for this instruction.
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SCEVHandle ISE = GetExpressionSCEV(I, L);
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if (isa<SCEVCouldNotCompute>(ISE)) return false;
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// Get the start and stride for this expression.
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SCEVHandle Start = SCEVUnknown::getIntegerSCEV(0, ISE->getType());
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SCEVHandle Stride = Start;
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if (!getSCEVStartAndStride(ISE, L, Start, Stride))
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return false; // Non-reducible symbolic expression, bail out.
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for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;++UI){
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Instruction *User = cast<Instruction>(*UI);
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// Do not infinitely recurse on PHI nodes.
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if (isa<PHINode>(User) && User->getParent() == L->getHeader())
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continue;
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// If this is an instruction defined in a nested loop, or outside this loop,
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// don't recurse into it.
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bool AddUserToIVUsers = false;
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if (LI->getLoopFor(User->getParent()) != L) {
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DEBUG(std::cerr << "FOUND USER in nested loop: " << *User
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<< " OF SCEV: " << *ISE << "\n");
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AddUserToIVUsers = true;
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} else if (!AddUsersIfInteresting(User, L, Processed)) {
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DEBUG(std::cerr << "FOUND USER: " << *User
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<< " OF SCEV: " << *ISE << "\n");
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AddUserToIVUsers = true;
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}
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if (AddUserToIVUsers) {
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// Okay, we found a user that we cannot reduce. Analyze the instruction
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// and decide what to do with it.
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IVUsesByStride[Stride].addUser(Start, User, I);
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}
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}
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return true;
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}
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namespace {
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/// BasedUser - For a particular base value, keep information about how we've
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/// partitioned the expression so far.
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struct BasedUser {
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/// Base - The Base value for the PHI node that needs to be inserted for
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/// this use. As the use is processed, information gets moved from this
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/// field to the Imm field (below). BasedUser values are sorted by this
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/// field.
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SCEVHandle Base;
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/// Inst - The instruction using the induction variable.
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Instruction *Inst;
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/// OperandValToReplace - The operand value of Inst to replace with the
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/// EmittedBase.
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Value *OperandValToReplace;
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/// Imm - The immediate value that should be added to the base immediately
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/// before Inst, because it will be folded into the imm field of the
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/// instruction.
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SCEVHandle Imm;
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/// EmittedBase - The actual value* to use for the base value of this
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/// operation. This is null if we should just use zero so far.
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Value *EmittedBase;
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// isUseOfPostIncrementedValue - True if this should use the
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// post-incremented version of this IV, not the preincremented version.
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// This can only be set in special cases, such as the terminating setcc
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// instruction for a loop.
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bool isUseOfPostIncrementedValue;
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BasedUser(IVStrideUse &IVSU)
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: Base(IVSU.Offset), Inst(IVSU.User),
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OperandValToReplace(IVSU.OperandValToReplace),
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Imm(SCEVUnknown::getIntegerSCEV(0, Base->getType())), EmittedBase(0),
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isUseOfPostIncrementedValue(IVSU.isUseOfPostIncrementedValue) {}
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// Once we rewrite the code to insert the new IVs we want, update the
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// operands of Inst to use the new expression 'NewBase', with 'Imm' added
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// to it.
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void RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
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SCEVExpander &Rewriter);
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// Sort by the Base field.
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bool operator<(const BasedUser &BU) const { return Base < BU.Base; }
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void dump() const;
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};
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}
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void BasedUser::dump() const {
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std::cerr << " Base=" << *Base;
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std::cerr << " Imm=" << *Imm;
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if (EmittedBase)
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std::cerr << " EB=" << *EmittedBase;
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std::cerr << " Inst: " << *Inst;
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}
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// Once we rewrite the code to insert the new IVs we want, update the
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// operands of Inst to use the new expression 'NewBase', with 'Imm' added
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// to it.
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void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
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SCEVExpander &Rewriter) {
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if (!isa<PHINode>(Inst)) {
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SCEVHandle NewValSCEV = SCEVAddExpr::get(NewBase, Imm);
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Value *NewVal = Rewriter.expandCodeFor(NewValSCEV, Inst,
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OperandValToReplace->getType());
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// Replace the use of the operand Value with the new Phi we just created.
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Inst->replaceUsesOfWith(OperandValToReplace, NewVal);
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DEBUG(std::cerr << " CHANGED: IMM =" << *Imm << " Inst = " << *Inst);
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return;
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}
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// PHI nodes are more complex. We have to insert one copy of the NewBase+Imm
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// expression into each operand block that uses it. Note that PHI nodes can
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// have multiple entries for the same predecessor. We use a map to make sure
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// that a PHI node only has a single Value* for each predecessor (which also
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// prevents us from inserting duplicate code in some blocks).
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std::map<BasicBlock*, Value*> InsertedCode;
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PHINode *PN = cast<PHINode>(Inst);
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
if (PN->getIncomingValue(i) == OperandValToReplace) {
|
|
// FIXME: this should split any critical edges.
|
|
|
|
Value *&Code = InsertedCode[PN->getIncomingBlock(i)];
|
|
if (!Code) {
|
|
// Insert the code into the end of the predecessor block.
|
|
BasicBlock::iterator InsertPt =PN->getIncomingBlock(i)->getTerminator();
|
|
|
|
SCEVHandle NewValSCEV = SCEVAddExpr::get(NewBase, Imm);
|
|
Code = Rewriter.expandCodeFor(NewValSCEV, InsertPt,
|
|
OperandValToReplace->getType());
|
|
}
|
|
|
|
// Replace the use of the operand Value with the new Phi we just created.
|
|
PN->setIncomingValue(i, Code);
|
|
Rewriter.clear();
|
|
}
|
|
}
|
|
DEBUG(std::cerr << " CHANGED: IMM =" << *Imm << " Inst = " << *Inst);
|
|
}
|
|
|
|
|
|
/// isTargetConstant - Return true if the following can be referenced by the
|
|
/// immediate field of a target instruction.
|
|
static bool isTargetConstant(const SCEVHandle &V) {
|
|
|
|
// FIXME: Look at the target to decide if &GV is a legal constant immediate.
|
|
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(V)) {
|
|
// PPC allows a sign-extended 16-bit immediate field.
|
|
if ((int64_t)SC->getValue()->getRawValue() > -(1 << 16) &&
|
|
(int64_t)SC->getValue()->getRawValue() < (1 << 16)-1)
|
|
return true;
|
|
return false;
|
|
}
|
|
|
|
return false; // ENABLE this for x86
|
|
|
|
if (SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V))
|
|
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(SU->getValue()))
|
|
if (CE->getOpcode() == Instruction::Cast)
|
|
if (isa<GlobalValue>(CE->getOperand(0)))
|
|
// FIXME: should check to see that the dest is uintptr_t!
|
|
return true;
|
|
return false;
|
|
}
|
|
|
|
/// MoveLoopVariantsToImediateField - Move any subexpressions from Val that are
|
|
/// loop varying to the Imm operand.
|
|
static void MoveLoopVariantsToImediateField(SCEVHandle &Val, SCEVHandle &Imm,
|
|
Loop *L) {
|
|
if (Val->isLoopInvariant(L)) return; // Nothing to do.
|
|
|
|
if (SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
|
|
std::vector<SCEVHandle> NewOps;
|
|
NewOps.reserve(SAE->getNumOperands());
|
|
|
|
for (unsigned i = 0; i != SAE->getNumOperands(); ++i)
|
|
if (!SAE->getOperand(i)->isLoopInvariant(L)) {
|
|
// If this is a loop-variant expression, it must stay in the immediate
|
|
// field of the expression.
|
|
Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
|
|
} else {
|
|
NewOps.push_back(SAE->getOperand(i));
|
|
}
|
|
|
|
if (NewOps.empty())
|
|
Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
|
|
else
|
|
Val = SCEVAddExpr::get(NewOps);
|
|
} else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
|
|
// Try to pull immediates out of the start value of nested addrec's.
|
|
SCEVHandle Start = SARE->getStart();
|
|
MoveLoopVariantsToImediateField(Start, Imm, L);
|
|
|
|
std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
|
|
Ops[0] = Start;
|
|
Val = SCEVAddRecExpr::get(Ops, SARE->getLoop());
|
|
} else {
|
|
// Otherwise, all of Val is variant, move the whole thing over.
|
|
Imm = SCEVAddExpr::get(Imm, Val);
|
|
Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
|
|
}
|
|
}
|
|
|
|
|
|
/// MoveImmediateValues - Look at Val, and pull out any additions of constants
|
|
/// that can fit into the immediate field of instructions in the target.
|
|
/// Accumulate these immediate values into the Imm value.
|
|
static void MoveImmediateValues(SCEVHandle &Val, SCEVHandle &Imm,
|
|
bool isAddress, Loop *L) {
|
|
if (SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) {
|
|
std::vector<SCEVHandle> NewOps;
|
|
NewOps.reserve(SAE->getNumOperands());
|
|
|
|
for (unsigned i = 0; i != SAE->getNumOperands(); ++i)
|
|
if (isAddress && isTargetConstant(SAE->getOperand(i))) {
|
|
Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
|
|
} else if (!SAE->getOperand(i)->isLoopInvariant(L)) {
|
|
// If this is a loop-variant expression, it must stay in the immediate
|
|
// field of the expression.
|
|
Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
|
|
} else {
|
|
NewOps.push_back(SAE->getOperand(i));
|
|
}
|
|
|
|
if (NewOps.empty())
|
|
Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
|
|
else
|
|
Val = SCEVAddExpr::get(NewOps);
|
|
return;
|
|
} else if (SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) {
|
|
// Try to pull immediates out of the start value of nested addrec's.
|
|
SCEVHandle Start = SARE->getStart();
|
|
MoveImmediateValues(Start, Imm, isAddress, L);
|
|
|
|
if (Start != SARE->getStart()) {
|
|
std::vector<SCEVHandle> Ops(SARE->op_begin(), SARE->op_end());
|
|
Ops[0] = Start;
|
|
Val = SCEVAddRecExpr::get(Ops, SARE->getLoop());
|
|
}
|
|
return;
|
|
}
|
|
|
|
// Loop-variant expressions must stay in the immediate field of the
|
|
// expression.
|
|
if ((isAddress && isTargetConstant(Val)) ||
|
|
!Val->isLoopInvariant(L)) {
|
|
Imm = SCEVAddExpr::get(Imm, Val);
|
|
Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
|
|
return;
|
|
}
|
|
|
|
// Otherwise, no immediates to move.
|
|
}
|
|
|
|
/// RemoveCommonExpressionsFromUseBases - Look through all of the uses in Bases,
|
|
/// removing any common subexpressions from it. Anything truly common is
|
|
/// removed, accumulated, and returned. This looks for things like (a+b+c) and
|
|
/// (a+c+d) -> (a+c). The common expression is *removed* from the Bases.
|
|
static SCEVHandle
|
|
RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses) {
|
|
unsigned NumUses = Uses.size();
|
|
|
|
// Only one use? Use its base, regardless of what it is!
|
|
SCEVHandle Zero = SCEVUnknown::getIntegerSCEV(0, Uses[0].Base->getType());
|
|
SCEVHandle Result = Zero;
|
|
if (NumUses == 1) {
|
|
std::swap(Result, Uses[0].Base);
|
|
return Result;
|
|
}
|
|
|
|
// To find common subexpressions, count how many of Uses use each expression.
|
|
// If any subexpressions are used Uses.size() times, they are common.
|
|
std::map<SCEVHandle, unsigned> SubExpressionUseCounts;
|
|
|
|
for (unsigned i = 0; i != NumUses; ++i)
|
|
if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Uses[i].Base)) {
|
|
for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j)
|
|
SubExpressionUseCounts[AE->getOperand(j)]++;
|
|
} else {
|
|
// If the base is zero (which is common), return zero now, there are no
|
|
// CSEs we can find.
|
|
if (Uses[i].Base == Zero) return Result;
|
|
SubExpressionUseCounts[Uses[i].Base]++;
|
|
}
|
|
|
|
// Now that we know how many times each is used, build Result.
|
|
for (std::map<SCEVHandle, unsigned>::iterator I =
|
|
SubExpressionUseCounts.begin(), E = SubExpressionUseCounts.end();
|
|
I != E; )
|
|
if (I->second == NumUses) { // Found CSE!
|
|
Result = SCEVAddExpr::get(Result, I->first);
|
|
++I;
|
|
} else {
|
|
// Remove non-cse's from SubExpressionUseCounts.
|
|
SubExpressionUseCounts.erase(I++);
|
|
}
|
|
|
|
// If we found no CSE's, return now.
|
|
if (Result == Zero) return Result;
|
|
|
|
// Otherwise, remove all of the CSE's we found from each of the base values.
|
|
for (unsigned i = 0; i != NumUses; ++i)
|
|
if (SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Uses[i].Base)) {
|
|
std::vector<SCEVHandle> NewOps;
|
|
|
|
// Remove all of the values that are now in SubExpressionUseCounts.
|
|
for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j)
|
|
if (!SubExpressionUseCounts.count(AE->getOperand(j)))
|
|
NewOps.push_back(AE->getOperand(j));
|
|
if (NewOps.size() == 0)
|
|
Uses[i].Base = Zero;
|
|
else
|
|
Uses[i].Base = SCEVAddExpr::get(NewOps);
|
|
} else {
|
|
// If the base is zero (which is common), return zero now, there are no
|
|
// CSEs we can find.
|
|
assert(Uses[i].Base == Result);
|
|
Uses[i].Base = Zero;
|
|
}
|
|
|
|
return Result;
|
|
}
|
|
|
|
|
|
/// StrengthReduceStridedIVUsers - Strength reduce all of the users of a single
|
|
/// stride of IV. All of the users may have different starting values, and this
|
|
/// may not be the only stride (we know it is if isOnlyStride is true).
|
|
void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
|
|
IVUsersOfOneStride &Uses,
|
|
Loop *L,
|
|
bool isOnlyStride) {
|
|
// Transform our list of users and offsets to a bit more complex table. In
|
|
// this new vector, each 'BasedUser' contains 'Base' the base of the
|
|
// strided accessas well as the old information from Uses. We progressively
|
|
// move information from the Base field to the Imm field, until we eventually
|
|
// have the full access expression to rewrite the use.
|
|
std::vector<BasedUser> UsersToProcess;
|
|
UsersToProcess.reserve(Uses.Users.size());
|
|
for (unsigned i = 0, e = Uses.Users.size(); i != e; ++i) {
|
|
UsersToProcess.push_back(Uses.Users[i]);
|
|
|
|
// Move any loop invariant operands from the offset field to the immediate
|
|
// field of the use, so that we don't try to use something before it is
|
|
// computed.
|
|
MoveLoopVariantsToImediateField(UsersToProcess.back().Base,
|
|
UsersToProcess.back().Imm, L);
|
|
assert(UsersToProcess.back().Base->isLoopInvariant(L) &&
|
|
"Base value is not loop invariant!");
|
|
}
|
|
|
|
// We now have a whole bunch of uses of like-strided induction variables, but
|
|
// they might all have different bases. We want to emit one PHI node for this
|
|
// stride which we fold as many common expressions (between the IVs) into as
|
|
// possible. Start by identifying the common expressions in the base values
|
|
// for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find
|
|
// "A+B"), emit it to the preheader, then remove the expression from the
|
|
// UsersToProcess base values.
|
|
SCEVHandle CommonExprs = RemoveCommonExpressionsFromUseBases(UsersToProcess);
|
|
|
|
// Next, figure out what we can represent in the immediate fields of
|
|
// instructions. If we can represent anything there, move it to the imm
|
|
// fields of the BasedUsers. We do this so that it increases the commonality
|
|
// of the remaining uses.
|
|
for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) {
|
|
// Addressing modes can be folded into loads and stores. Be careful that
|
|
// the store is through the expression, not of the expression though.
|
|
bool isAddress = isa<LoadInst>(UsersToProcess[i].Inst);
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(UsersToProcess[i].Inst))
|
|
if (SI->getOperand(1) == UsersToProcess[i].OperandValToReplace)
|
|
isAddress = true;
|
|
|
|
MoveImmediateValues(UsersToProcess[i].Base, UsersToProcess[i].Imm,
|
|
isAddress, L);
|
|
}
|
|
|
|
// Now that we know what we need to do, insert the PHI node itself.
|
|
//
|
|
DEBUG(std::cerr << "INSERTING IV of STRIDE " << *Stride << " and BASE "
|
|
<< *CommonExprs << " :\n");
|
|
|
|
SCEVExpander Rewriter(*SE, *LI);
|
|
SCEVExpander PreheaderRewriter(*SE, *LI);
|
|
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
Instruction *PreInsertPt = Preheader->getTerminator();
|
|
Instruction *PhiInsertBefore = L->getHeader()->begin();
|
|
|
|
assert(isa<PHINode>(PhiInsertBefore) &&
|
|
"How could this loop have IV's without any phis?");
|
|
PHINode *SomeLoopPHI = cast<PHINode>(PhiInsertBefore);
|
|
assert(SomeLoopPHI->getNumIncomingValues() == 2 &&
|
|
"This loop isn't canonicalized right");
|
|
BasicBlock *LatchBlock =
|
|
SomeLoopPHI->getIncomingBlock(SomeLoopPHI->getIncomingBlock(0) == Preheader);
|
|
|
|
// Create a new Phi for this base, and stick it in the loop header.
|
|
const Type *ReplacedTy = CommonExprs->getType();
|
|
PHINode *NewPHI = new PHINode(ReplacedTy, "iv.", PhiInsertBefore);
|
|
++NumInserted;
|
|
|
|
// Insert the stride into the preheader.
|
|
Value *StrideV = PreheaderRewriter.expandCodeFor(Stride, PreInsertPt,
|
|
ReplacedTy);
|
|
if (!isa<ConstantInt>(StrideV)) ++NumVariable;
|
|
|
|
|
|
// Emit the initial base value into the loop preheader, and add it to the
|
|
// Phi node.
|
|
Value *PHIBaseV = PreheaderRewriter.expandCodeFor(CommonExprs, PreInsertPt,
|
|
ReplacedTy);
|
|
NewPHI->addIncoming(PHIBaseV, Preheader);
|
|
|
|
// Emit the increment of the base value before the terminator of the loop
|
|
// latch block, and add it to the Phi node.
|
|
SCEVHandle IncExp = SCEVAddExpr::get(SCEVUnknown::get(NewPHI),
|
|
SCEVUnknown::get(StrideV));
|
|
|
|
Value *IncV = Rewriter.expandCodeFor(IncExp, LatchBlock->getTerminator(),
|
|
ReplacedTy);
|
|
IncV->setName(NewPHI->getName()+".inc");
|
|
NewPHI->addIncoming(IncV, LatchBlock);
|
|
|
|
// Sort by the base value, so that all IVs with identical bases are next to
|
|
// each other.
|
|
std::sort(UsersToProcess.begin(), UsersToProcess.end());
|
|
while (!UsersToProcess.empty()) {
|
|
SCEVHandle Base = UsersToProcess.front().Base;
|
|
|
|
DEBUG(std::cerr << " INSERTING code for BASE = " << *Base << ":\n");
|
|
|
|
// Emit the code for Base into the preheader.
|
|
Value *BaseV = PreheaderRewriter.expandCodeFor(Base, PreInsertPt,
|
|
ReplacedTy);
|
|
|
|
// If BaseV is a constant other than 0, make sure that it gets inserted into
|
|
// the preheader, instead of being forward substituted into the uses. We do
|
|
// this by forcing a noop cast to be inserted into the preheader in this
|
|
// case.
|
|
if (Constant *C = dyn_cast<Constant>(BaseV))
|
|
if (!C->isNullValue()) {
|
|
// We want this constant emitted into the preheader!
|
|
BaseV = new CastInst(BaseV, BaseV->getType(), "preheaderinsert",
|
|
PreInsertPt);
|
|
}
|
|
|
|
// Emit the code to add the immediate offset to the Phi value, just before
|
|
// the instructions that we identified as using this stride and base.
|
|
while (!UsersToProcess.empty() && UsersToProcess.front().Base == Base) {
|
|
BasedUser &User = UsersToProcess.front();
|
|
|
|
// If this instruction wants to use the post-incremented value, move it
|
|
// after the post-inc and use its value instead of the PHI.
|
|
Value *RewriteOp = NewPHI;
|
|
if (User.isUseOfPostIncrementedValue) {
|
|
RewriteOp = IncV;
|
|
User.Inst->moveBefore(LatchBlock->getTerminator());
|
|
}
|
|
SCEVHandle RewriteExpr = SCEVUnknown::get(RewriteOp);
|
|
|
|
// Clear the SCEVExpander's expression map so that we are guaranteed
|
|
// to have the code emitted where we expect it.
|
|
Rewriter.clear();
|
|
|
|
// Now that we know what we need to do, insert code before User for the
|
|
// immediate and any loop-variant expressions.
|
|
if (!isa<ConstantInt>(BaseV) || !cast<ConstantInt>(BaseV)->isNullValue())
|
|
// Add BaseV to the PHI value if needed.
|
|
RewriteExpr = SCEVAddExpr::get(RewriteExpr, SCEVUnknown::get(BaseV));
|
|
|
|
User.RewriteInstructionToUseNewBase(RewriteExpr, Rewriter);
|
|
|
|
// Mark old value we replaced as possibly dead, so that it is elminated
|
|
// if we just replaced the last use of that value.
|
|
DeadInsts.insert(cast<Instruction>(User.OperandValToReplace));
|
|
|
|
UsersToProcess.erase(UsersToProcess.begin());
|
|
++NumReduced;
|
|
}
|
|
// TODO: Next, find out which base index is the most common, pull it out.
|
|
}
|
|
|
|
// IMPORTANT TODO: Figure out how to partition the IV's with this stride, but
|
|
// different starting values, into different PHIs.
|
|
}
|
|
|
|
// OptimizeIndvars - Now that IVUsesByStride is set up with all of the indvar
|
|
// uses in the loop, look to see if we can eliminate some, in favor of using
|
|
// common indvars for the different uses.
|
|
void LoopStrengthReduce::OptimizeIndvars(Loop *L) {
|
|
// TODO: implement optzns here.
|
|
|
|
|
|
|
|
|
|
// Finally, get the terminating condition for the loop if possible. If we
|
|
// can, we want to change it to use a post-incremented version of its
|
|
// induction variable, to allow coallescing the live ranges for the IV into
|
|
// one register value.
|
|
PHINode *SomePHI = cast<PHINode>(L->getHeader()->begin());
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
BasicBlock *LatchBlock =
|
|
SomePHI->getIncomingBlock(SomePHI->getIncomingBlock(0) == Preheader);
|
|
BranchInst *TermBr = dyn_cast<BranchInst>(LatchBlock->getTerminator());
|
|
if (!TermBr || TermBr->isUnconditional() ||
|
|
!isa<SetCondInst>(TermBr->getCondition()))
|
|
return;
|
|
SetCondInst *Cond = cast<SetCondInst>(TermBr->getCondition());
|
|
|
|
// Search IVUsesByStride to find Cond's IVUse if there is one.
|
|
IVStrideUse *CondUse = 0;
|
|
const SCEVHandle *CondStride = 0;
|
|
|
|
for (std::map<SCEVHandle, IVUsersOfOneStride>::iterator
|
|
I = IVUsesByStride.begin(), E = IVUsesByStride.end();
|
|
I != E && !CondUse; ++I)
|
|
for (std::vector<IVStrideUse>::iterator UI = I->second.Users.begin(),
|
|
E = I->second.Users.end(); UI != E; ++UI)
|
|
if (UI->User == Cond) {
|
|
CondUse = &*UI;
|
|
CondStride = &I->first;
|
|
// NOTE: we could handle setcc instructions with multiple uses here, but
|
|
// InstCombine does it as well for simple uses, it's not clear that it
|
|
// occurs enough in real life to handle.
|
|
break;
|
|
}
|
|
if (!CondUse) return; // setcc doesn't use the IV.
|
|
|
|
// setcc stride is complex, don't mess with users.
|
|
// FIXME: Evaluate whether this is a good idea or not.
|
|
if (!isa<SCEVConstant>(*CondStride)) return;
|
|
|
|
// It's possible for the setcc instruction to be anywhere in the loop, and
|
|
// possible for it to have multiple users. If it is not immediately before
|
|
// the latch block branch, move it.
|
|
if (&*++BasicBlock::iterator(Cond) != (Instruction*)TermBr) {
|
|
if (Cond->hasOneUse()) { // Condition has a single use, just move it.
|
|
Cond->moveBefore(TermBr);
|
|
} else {
|
|
// Otherwise, clone the terminating condition and insert into the loopend.
|
|
Cond = cast<SetCondInst>(Cond->clone());
|
|
Cond->setName(L->getHeader()->getName() + ".termcond");
|
|
LatchBlock->getInstList().insert(TermBr, Cond);
|
|
|
|
// Clone the IVUse, as the old use still exists!
|
|
IVUsesByStride[*CondStride].addUser(CondUse->Offset, Cond,
|
|
CondUse->OperandValToReplace);
|
|
CondUse = &IVUsesByStride[*CondStride].Users.back();
|
|
}
|
|
}
|
|
|
|
// If we get to here, we know that we can transform the setcc instruction to
|
|
// use the post-incremented version of the IV, allowing us to coallesce the
|
|
// live ranges for the IV correctly.
|
|
CondUse->Offset = SCEV::getMinusSCEV(CondUse->Offset, *CondStride);
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|
CondUse->isUseOfPostIncrementedValue = true;
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|
}
|
|
|
|
void LoopStrengthReduce::runOnLoop(Loop *L) {
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|
// First step, transform all loops nesting inside of this loop.
|
|
for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I)
|
|
runOnLoop(*I);
|
|
|
|
// Next, find all uses of induction variables in this loop, and catagorize
|
|
// them by stride. Start by finding all of the PHI nodes in the header for
|
|
// this loop. If they are induction variables, inspect their uses.
|
|
std::set<Instruction*> Processed; // Don't reprocess instructions.
|
|
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
|
|
AddUsersIfInteresting(I, L, Processed);
|
|
|
|
// If we have nothing to do, return.
|
|
if (IVUsesByStride.empty()) return;
|
|
|
|
// Optimize induction variables. Some indvar uses can be transformed to use
|
|
// strides that will be needed for other purposes. A common example of this
|
|
// is the exit test for the loop, which can often be rewritten to use the
|
|
// computation of some other indvar to decide when to terminate the loop.
|
|
OptimizeIndvars(L);
|
|
|
|
|
|
// FIXME: We can widen subreg IV's here for RISC targets. e.g. instead of
|
|
// doing computation in byte values, promote to 32-bit values if safe.
|
|
|
|
// FIXME: Attempt to reuse values across multiple IV's. In particular, we
|
|
// could have something like "for(i) { foo(i*8); bar(i*16) }", which should be
|
|
// codegened as "for (j = 0;; j+=8) { foo(j); bar(j+j); }" on X86/PPC. Need
|
|
// to be careful that IV's are all the same type. Only works for intptr_t
|
|
// indvars.
|
|
|
|
// If we only have one stride, we can more aggressively eliminate some things.
|
|
bool HasOneStride = IVUsesByStride.size() == 1;
|
|
|
|
// Note: this processes each stride/type pair individually. All users passed
|
|
// into StrengthReduceStridedIVUsers have the same type AND stride.
|
|
for (std::map<SCEVHandle, IVUsersOfOneStride>::iterator SI
|
|
= IVUsesByStride.begin(), E = IVUsesByStride.end(); SI != E; ++SI)
|
|
StrengthReduceStridedIVUsers(SI->first, SI->second, L, HasOneStride);
|
|
|
|
// Clean up after ourselves
|
|
if (!DeadInsts.empty()) {
|
|
DeleteTriviallyDeadInstructions(DeadInsts);
|
|
|
|
BasicBlock::iterator I = L->getHeader()->begin();
|
|
PHINode *PN;
|
|
while ((PN = dyn_cast<PHINode>(I))) {
|
|
++I; // Preincrement iterator to avoid invalidating it when deleting PN.
|
|
|
|
// At this point, we know that we have killed one or more GEP
|
|
// instructions. It is worth checking to see if the cann indvar is also
|
|
// dead, so that we can remove it as well. The requirements for the cann
|
|
// indvar to be considered dead are:
|
|
// 1. the cann indvar has one use
|
|
// 2. the use is an add instruction
|
|
// 3. the add has one use
|
|
// 4. the add is used by the cann indvar
|
|
// If all four cases above are true, then we can remove both the add and
|
|
// the cann indvar.
|
|
// FIXME: this needs to eliminate an induction variable even if it's being
|
|
// compared against some value to decide loop termination.
|
|
if (PN->hasOneUse()) {
|
|
BinaryOperator *BO = dyn_cast<BinaryOperator>(*(PN->use_begin()));
|
|
if (BO && BO->hasOneUse()) {
|
|
if (PN == *(BO->use_begin())) {
|
|
DeadInsts.insert(BO);
|
|
// Break the cycle, then delete the PHI.
|
|
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
|
|
SE->deleteInstructionFromRecords(PN);
|
|
PN->eraseFromParent();
|
|
}
|
|
}
|
|
}
|
|
}
|
|
DeleteTriviallyDeadInstructions(DeadInsts);
|
|
}
|
|
|
|
CastedPointers.clear();
|
|
IVUsesByStride.clear();
|
|
return;
|
|
}
|