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062c0daef0
This is a resubmission of previously reverted r277592. It was hitting overly strong assertion in getConstantRange which was relaxed in r278217. Use LVI to prove that adds do not wrap. The change is motivated by https://llvm.org/bugs/show_bug.cgi?id=28620 bug and it's the first step to fix that problem. Reviewed By: sanjoy Differential Revision: http://reviews.llvm.org/D23059 llvm-svn: 278220
550 lines
18 KiB
C++
550 lines
18 KiB
C++
//===- CorrelatedValuePropagation.cpp - Propagate CFG-derived info --------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the Correlated Value Propagation pass.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar/CorrelatedValuePropagation.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/GlobalsModRef.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LazyValueInfo.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/ConstantRange.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/Local.h"
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using namespace llvm;
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#define DEBUG_TYPE "correlated-value-propagation"
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STATISTIC(NumPhis, "Number of phis propagated");
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STATISTIC(NumSelects, "Number of selects propagated");
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STATISTIC(NumMemAccess, "Number of memory access targets propagated");
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STATISTIC(NumCmps, "Number of comparisons propagated");
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STATISTIC(NumReturns, "Number of return values propagated");
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STATISTIC(NumDeadCases, "Number of switch cases removed");
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STATISTIC(NumSDivs, "Number of sdiv converted to udiv");
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STATISTIC(NumSRems, "Number of srem converted to urem");
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namespace {
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class CorrelatedValuePropagation : public FunctionPass {
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public:
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static char ID;
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CorrelatedValuePropagation(): FunctionPass(ID) {
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initializeCorrelatedValuePropagationPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<LazyValueInfoWrapperPass>();
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AU.addPreserved<GlobalsAAWrapperPass>();
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}
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};
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}
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char CorrelatedValuePropagation::ID = 0;
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INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation",
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"Value Propagation", false, false)
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INITIALIZE_PASS_DEPENDENCY(LazyValueInfoWrapperPass)
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INITIALIZE_PASS_END(CorrelatedValuePropagation, "correlated-propagation",
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"Value Propagation", false, false)
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// Public interface to the Value Propagation pass
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Pass *llvm::createCorrelatedValuePropagationPass() {
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return new CorrelatedValuePropagation();
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}
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static bool processSelect(SelectInst *S, LazyValueInfo *LVI) {
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if (S->getType()->isVectorTy()) return false;
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if (isa<Constant>(S->getOperand(0))) return false;
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Constant *C = LVI->getConstant(S->getOperand(0), S->getParent(), S);
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if (!C) return false;
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ConstantInt *CI = dyn_cast<ConstantInt>(C);
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if (!CI) return false;
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Value *ReplaceWith = S->getOperand(1);
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Value *Other = S->getOperand(2);
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if (!CI->isOne()) std::swap(ReplaceWith, Other);
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if (ReplaceWith == S) ReplaceWith = UndefValue::get(S->getType());
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S->replaceAllUsesWith(ReplaceWith);
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S->eraseFromParent();
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++NumSelects;
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return true;
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}
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static bool processPHI(PHINode *P, LazyValueInfo *LVI) {
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bool Changed = false;
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BasicBlock *BB = P->getParent();
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for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
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Value *Incoming = P->getIncomingValue(i);
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if (isa<Constant>(Incoming)) continue;
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Value *V = LVI->getConstantOnEdge(Incoming, P->getIncomingBlock(i), BB, P);
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// Look if the incoming value is a select with a scalar condition for which
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// LVI can tells us the value. In that case replace the incoming value with
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// the appropriate value of the select. This often allows us to remove the
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// select later.
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if (!V) {
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SelectInst *SI = dyn_cast<SelectInst>(Incoming);
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if (!SI) continue;
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Value *Condition = SI->getCondition();
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if (!Condition->getType()->isVectorTy()) {
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if (Constant *C = LVI->getConstantOnEdge(
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Condition, P->getIncomingBlock(i), BB, P)) {
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if (C->isOneValue()) {
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V = SI->getTrueValue();
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} else if (C->isZeroValue()) {
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V = SI->getFalseValue();
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}
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// Once LVI learns to handle vector types, we could also add support
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// for vector type constants that are not all zeroes or all ones.
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}
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}
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// Look if the select has a constant but LVI tells us that the incoming
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// value can never be that constant. In that case replace the incoming
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// value with the other value of the select. This often allows us to
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// remove the select later.
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if (!V) {
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Constant *C = dyn_cast<Constant>(SI->getFalseValue());
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if (!C) continue;
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if (LVI->getPredicateOnEdge(ICmpInst::ICMP_EQ, SI, C,
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P->getIncomingBlock(i), BB, P) !=
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LazyValueInfo::False)
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continue;
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V = SI->getTrueValue();
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}
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DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
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}
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P->setIncomingValue(i, V);
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Changed = true;
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}
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// FIXME: Provide TLI, DT, AT to SimplifyInstruction.
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const DataLayout &DL = BB->getModule()->getDataLayout();
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if (Value *V = SimplifyInstruction(P, DL)) {
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P->replaceAllUsesWith(V);
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P->eraseFromParent();
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Changed = true;
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}
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if (Changed)
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++NumPhis;
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return Changed;
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}
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static bool processMemAccess(Instruction *I, LazyValueInfo *LVI) {
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Value *Pointer = nullptr;
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if (LoadInst *L = dyn_cast<LoadInst>(I))
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Pointer = L->getPointerOperand();
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else
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Pointer = cast<StoreInst>(I)->getPointerOperand();
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if (isa<Constant>(Pointer)) return false;
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Constant *C = LVI->getConstant(Pointer, I->getParent(), I);
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if (!C) return false;
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++NumMemAccess;
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I->replaceUsesOfWith(Pointer, C);
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return true;
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}
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/// See if LazyValueInfo's ability to exploit edge conditions or range
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/// information is sufficient to prove this comparison. Even for local
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/// conditions, this can sometimes prove conditions instcombine can't by
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/// exploiting range information.
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static bool processCmp(CmpInst *C, LazyValueInfo *LVI) {
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Value *Op0 = C->getOperand(0);
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Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
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if (!Op1) return false;
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// As a policy choice, we choose not to waste compile time on anything where
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// the comparison is testing local values. While LVI can sometimes reason
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// about such cases, it's not its primary purpose. We do make sure to do
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// the block local query for uses from terminator instructions, but that's
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// handled in the code for each terminator.
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auto *I = dyn_cast<Instruction>(Op0);
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if (I && I->getParent() == C->getParent())
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return false;
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LazyValueInfo::Tristate Result =
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LVI->getPredicateAt(C->getPredicate(), Op0, Op1, C);
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if (Result == LazyValueInfo::Unknown) return false;
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++NumCmps;
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if (Result == LazyValueInfo::True)
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C->replaceAllUsesWith(ConstantInt::getTrue(C->getContext()));
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else
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C->replaceAllUsesWith(ConstantInt::getFalse(C->getContext()));
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C->eraseFromParent();
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return true;
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}
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/// Simplify a switch instruction by removing cases which can never fire. If the
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/// uselessness of a case could be determined locally then constant propagation
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/// would already have figured it out. Instead, walk the predecessors and
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/// statically evaluate cases based on information available on that edge. Cases
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/// that cannot fire no matter what the incoming edge can safely be removed. If
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/// a case fires on every incoming edge then the entire switch can be removed
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/// and replaced with a branch to the case destination.
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static bool processSwitch(SwitchInst *SI, LazyValueInfo *LVI) {
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Value *Cond = SI->getCondition();
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BasicBlock *BB = SI->getParent();
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// If the condition was defined in same block as the switch then LazyValueInfo
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// currently won't say anything useful about it, though in theory it could.
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if (isa<Instruction>(Cond) && cast<Instruction>(Cond)->getParent() == BB)
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return false;
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// If the switch is unreachable then trying to improve it is a waste of time.
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pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
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if (PB == PE) return false;
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// Analyse each switch case in turn. This is done in reverse order so that
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// removing a case doesn't cause trouble for the iteration.
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bool Changed = false;
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for (SwitchInst::CaseIt CI = SI->case_end(), CE = SI->case_begin(); CI-- != CE;
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) {
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ConstantInt *Case = CI.getCaseValue();
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// Check to see if the switch condition is equal to/not equal to the case
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// value on every incoming edge, equal/not equal being the same each time.
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LazyValueInfo::Tristate State = LazyValueInfo::Unknown;
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for (pred_iterator PI = PB; PI != PE; ++PI) {
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// Is the switch condition equal to the case value?
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LazyValueInfo::Tristate Value = LVI->getPredicateOnEdge(CmpInst::ICMP_EQ,
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Cond, Case, *PI,
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BB, SI);
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// Give up on this case if nothing is known.
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if (Value == LazyValueInfo::Unknown) {
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State = LazyValueInfo::Unknown;
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break;
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}
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// If this was the first edge to be visited, record that all other edges
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// need to give the same result.
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if (PI == PB) {
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State = Value;
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continue;
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}
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// If this case is known to fire for some edges and known not to fire for
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// others then there is nothing we can do - give up.
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if (Value != State) {
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State = LazyValueInfo::Unknown;
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break;
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}
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}
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if (State == LazyValueInfo::False) {
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// This case never fires - remove it.
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CI.getCaseSuccessor()->removePredecessor(BB);
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SI->removeCase(CI); // Does not invalidate the iterator.
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// The condition can be modified by removePredecessor's PHI simplification
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// logic.
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Cond = SI->getCondition();
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++NumDeadCases;
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Changed = true;
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} else if (State == LazyValueInfo::True) {
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// This case always fires. Arrange for the switch to be turned into an
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// unconditional branch by replacing the switch condition with the case
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// value.
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SI->setCondition(Case);
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NumDeadCases += SI->getNumCases();
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Changed = true;
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break;
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}
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}
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if (Changed)
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// If the switch has been simplified to the point where it can be replaced
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// by a branch then do so now.
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ConstantFoldTerminator(BB);
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return Changed;
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}
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/// Infer nonnull attributes for the arguments at the specified callsite.
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static bool processCallSite(CallSite CS, LazyValueInfo *LVI) {
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SmallVector<unsigned, 4> Indices;
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unsigned ArgNo = 0;
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for (Value *V : CS.args()) {
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PointerType *Type = dyn_cast<PointerType>(V->getType());
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// Try to mark pointer typed parameters as non-null. We skip the
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// relatively expensive analysis for constants which are obviously either
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// null or non-null to start with.
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if (Type && !CS.paramHasAttr(ArgNo + 1, Attribute::NonNull) &&
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!isa<Constant>(V) &&
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LVI->getPredicateAt(ICmpInst::ICMP_EQ, V,
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ConstantPointerNull::get(Type),
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CS.getInstruction()) == LazyValueInfo::False)
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Indices.push_back(ArgNo + 1);
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ArgNo++;
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}
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assert(ArgNo == CS.arg_size() && "sanity check");
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if (Indices.empty())
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return false;
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AttributeSet AS = CS.getAttributes();
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LLVMContext &Ctx = CS.getInstruction()->getContext();
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AS = AS.addAttribute(Ctx, Indices, Attribute::get(Ctx, Attribute::NonNull));
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CS.setAttributes(AS);
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return true;
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}
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// Helper function to rewrite srem and sdiv. As a policy choice, we choose not
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// to waste compile time on anything where the operands are local defs. While
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// LVI can sometimes reason about such cases, it's not its primary purpose.
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static bool hasLocalDefs(BinaryOperator *SDI) {
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for (Value *O : SDI->operands()) {
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auto *I = dyn_cast<Instruction>(O);
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if (I && I->getParent() == SDI->getParent())
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return true;
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}
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return false;
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}
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static bool hasPositiveOperands(BinaryOperator *SDI, LazyValueInfo *LVI) {
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Constant *Zero = ConstantInt::get(SDI->getType(), 0);
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for (Value *O : SDI->operands()) {
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auto Result = LVI->getPredicateAt(ICmpInst::ICMP_SGE, O, Zero, SDI);
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if (Result != LazyValueInfo::True)
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return false;
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}
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return true;
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}
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static bool processSRem(BinaryOperator *SDI, LazyValueInfo *LVI) {
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if (SDI->getType()->isVectorTy() || hasLocalDefs(SDI) ||
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!hasPositiveOperands(SDI, LVI))
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return false;
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++NumSRems;
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auto *BO = BinaryOperator::CreateURem(SDI->getOperand(0), SDI->getOperand(1),
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SDI->getName(), SDI);
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SDI->replaceAllUsesWith(BO);
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SDI->eraseFromParent();
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return true;
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}
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/// See if LazyValueInfo's ability to exploit edge conditions or range
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/// information is sufficient to prove the both operands of this SDiv are
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/// positive. If this is the case, replace the SDiv with a UDiv. Even for local
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/// conditions, this can sometimes prove conditions instcombine can't by
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/// exploiting range information.
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static bool processSDiv(BinaryOperator *SDI, LazyValueInfo *LVI) {
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if (SDI->getType()->isVectorTy() || hasLocalDefs(SDI) ||
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!hasPositiveOperands(SDI, LVI))
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return false;
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++NumSDivs;
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auto *BO = BinaryOperator::CreateUDiv(SDI->getOperand(0), SDI->getOperand(1),
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SDI->getName(), SDI);
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BO->setIsExact(SDI->isExact());
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SDI->replaceAllUsesWith(BO);
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SDI->eraseFromParent();
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return true;
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}
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static bool processAdd(BinaryOperator *AddOp, LazyValueInfo *LVI) {
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typedef OverflowingBinaryOperator OBO;
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if (AddOp->getType()->isVectorTy() || hasLocalDefs(AddOp))
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return false;
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bool NSW = AddOp->hasNoSignedWrap();
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bool NUW = AddOp->hasNoUnsignedWrap();
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if (NSW && NUW)
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return false;
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BasicBlock *BB = AddOp->getParent();
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Value *LHS = AddOp->getOperand(0);
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Value *RHS = AddOp->getOperand(1);
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ConstantRange LRange = LVI->getConstantRange(LHS, BB, AddOp);
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// Initialize RRange only if we need it. If we know that guaranteed no wrap
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// range for the given LHS range is empty don't spend time calculating the
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// range for the RHS.
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Optional<ConstantRange> RRange;
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auto LazyRRange = [&] () {
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if (!RRange)
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RRange = LVI->getConstantRange(RHS, BB, AddOp);
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return RRange.getValue();
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};
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bool Changed = false;
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if (!NUW) {
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ConstantRange NUWRange =
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LRange.makeGuaranteedNoWrapRegion(BinaryOperator::Add, LRange,
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OBO::NoUnsignedWrap);
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if (!NUWRange.isEmptySet()) {
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bool NewNUW = NUWRange.contains(LazyRRange());
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AddOp->setHasNoUnsignedWrap(NewNUW);
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Changed |= NewNUW;
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}
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}
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if (!NSW) {
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ConstantRange NSWRange =
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LRange.makeGuaranteedNoWrapRegion(BinaryOperator::Add, LRange,
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OBO::NoSignedWrap);
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if (!NSWRange.isEmptySet()) {
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bool NewNSW = NSWRange.contains(LazyRRange());
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AddOp->setHasNoSignedWrap(NewNSW);
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Changed |= NewNSW;
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}
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}
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return Changed;
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}
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static Constant *getConstantAt(Value *V, Instruction *At, LazyValueInfo *LVI) {
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if (Constant *C = LVI->getConstant(V, At->getParent(), At))
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return C;
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// TODO: The following really should be sunk inside LVI's core algorithm, or
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// at least the outer shims around such.
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auto *C = dyn_cast<CmpInst>(V);
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if (!C) return nullptr;
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Value *Op0 = C->getOperand(0);
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Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
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if (!Op1) return nullptr;
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LazyValueInfo::Tristate Result =
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LVI->getPredicateAt(C->getPredicate(), Op0, Op1, At);
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if (Result == LazyValueInfo::Unknown)
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return nullptr;
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return (Result == LazyValueInfo::True) ?
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ConstantInt::getTrue(C->getContext()) :
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ConstantInt::getFalse(C->getContext());
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}
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static bool runImpl(Function &F, LazyValueInfo *LVI) {
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bool FnChanged = false;
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for (BasicBlock &BB : F) {
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bool BBChanged = false;
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for (BasicBlock::iterator BI = BB.begin(), BE = BB.end(); BI != BE;) {
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Instruction *II = &*BI++;
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switch (II->getOpcode()) {
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case Instruction::Select:
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BBChanged |= processSelect(cast<SelectInst>(II), LVI);
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break;
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case Instruction::PHI:
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BBChanged |= processPHI(cast<PHINode>(II), LVI);
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break;
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case Instruction::ICmp:
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case Instruction::FCmp:
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BBChanged |= processCmp(cast<CmpInst>(II), LVI);
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break;
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case Instruction::Load:
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case Instruction::Store:
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BBChanged |= processMemAccess(II, LVI);
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break;
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case Instruction::Call:
|
|
case Instruction::Invoke:
|
|
BBChanged |= processCallSite(CallSite(II), LVI);
|
|
break;
|
|
case Instruction::SRem:
|
|
BBChanged |= processSRem(cast<BinaryOperator>(II), LVI);
|
|
break;
|
|
case Instruction::SDiv:
|
|
BBChanged |= processSDiv(cast<BinaryOperator>(II), LVI);
|
|
break;
|
|
case Instruction::Add:
|
|
BBChanged |= processAdd(cast<BinaryOperator>(II), LVI);
|
|
break;
|
|
}
|
|
}
|
|
|
|
Instruction *Term = BB.getTerminator();
|
|
switch (Term->getOpcode()) {
|
|
case Instruction::Switch:
|
|
BBChanged |= processSwitch(cast<SwitchInst>(Term), LVI);
|
|
break;
|
|
case Instruction::Ret: {
|
|
auto *RI = cast<ReturnInst>(Term);
|
|
// Try to determine the return value if we can. This is mainly here to
|
|
// simplify the writing of unit tests, but also helps to enable IPO by
|
|
// constant folding the return values of callees.
|
|
auto *RetVal = RI->getReturnValue();
|
|
if (!RetVal) break; // handle "ret void"
|
|
if (isa<Constant>(RetVal)) break; // nothing to do
|
|
if (auto *C = getConstantAt(RetVal, RI, LVI)) {
|
|
++NumReturns;
|
|
RI->replaceUsesOfWith(RetVal, C);
|
|
BBChanged = true;
|
|
}
|
|
}
|
|
};
|
|
|
|
FnChanged |= BBChanged;
|
|
}
|
|
|
|
return FnChanged;
|
|
}
|
|
|
|
bool CorrelatedValuePropagation::runOnFunction(Function &F) {
|
|
if (skipFunction(F))
|
|
return false;
|
|
|
|
LazyValueInfo *LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
|
|
return runImpl(F, LVI);
|
|
}
|
|
|
|
PreservedAnalyses
|
|
CorrelatedValuePropagationPass::run(Function &F, FunctionAnalysisManager &AM) {
|
|
|
|
LazyValueInfo *LVI = &AM.getResult<LazyValueAnalysis>(F);
|
|
bool Changed = runImpl(F, LVI);
|
|
|
|
// FIXME: We need to invalidate LVI to avoid PR28400. Is there a better
|
|
// solution?
|
|
AM.invalidate<LazyValueAnalysis>(F);
|
|
|
|
if (!Changed)
|
|
return PreservedAnalyses::all();
|
|
PreservedAnalyses PA;
|
|
PA.preserve<GlobalsAA>();
|
|
return PA;
|
|
}
|