diff --git a/llvm/include/llvm/Analysis/PostDominators.h b/llvm/include/llvm/Analysis/PostDominators.h --- a/llvm/include/llvm/Analysis/PostDominators.h +++ b/llvm/include/llvm/Analysis/PostDominators.h @@ -34,6 +34,13 @@ /// Handle invalidation explicitly. bool invalidate(Function &F, const PreservedAnalyses &PA, FunctionAnalysisManager::Invalidator &); + + // Ensure base-class overloads are visible. + using Base::dominates; + + /// Return true if \p I1 dominates \p I2. This checks if \p I2 comes before + /// \p I1 if they belongs to the same basic block. + bool dominates(const Instruction *I1, const Instruction *I2) const; }; /// Analysis pass which computes a \c PostDominatorTree. diff --git a/llvm/include/llvm/Transforms/Utils/CodeMoverUtils.h b/llvm/include/llvm/Transforms/Utils/CodeMoverUtils.h new file mode 100644 --- /dev/null +++ b/llvm/include/llvm/Transforms/Utils/CodeMoverUtils.h @@ -0,0 +1,40 @@ +//===- Transform/Utils/CodeMoverUtils.h - CodeMover Utils -------*- C++ -*-===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This family of functions determine movements are safe on basic blocks, and +// instructions contained within a function. +// +//===----------------------------------------------------------------------===// + +#ifndef LLVM_TRANSFORMS_UTILS_CODEMOVERUTILS_H +#define LLVM_TRANSFORMS_UTILS_CODEMOVERUTILS_H + +namespace llvm { + +class DependenceInfo; +class DominatorTree; +class Instruction; +class PostDominatorTree; + +/// Return true if \p I0 and \p I1 are control flow equivalent. +/// Two instructions are control flow equivalent if when one executes, +/// the other is guaranteed to execute. This is determined using dominators +/// and post-dominators: if A dominates B and B post-dominates A then A and B +/// are control-flow equivalent. +bool isControlFlowEquivalent(const Instruction &I0, const Instruction &I1, + const DominatorTree &DT, + const PostDominatorTree &PDT); + +/// Return true if \p I can be safely moved before \p InsertPoint. +bool isSafeToMoveBefore(Instruction &I, Instruction &InsertPoint, + const DominatorTree &DT, const PostDominatorTree &PDT, + DependenceInfo &DI); + +} // end namespace llvm + +#endif // LLVM_TRANSFORMS_UTILS_CODEMOVERUTILS_H diff --git a/llvm/lib/Analysis/PostDominators.cpp b/llvm/lib/Analysis/PostDominators.cpp --- a/llvm/lib/Analysis/PostDominators.cpp +++ b/llvm/lib/Analysis/PostDominators.cpp @@ -12,6 +12,7 @@ #include "llvm/Analysis/PostDominators.h" #include "llvm/IR/Function.h" +#include "llvm/IR/Instructions.h" #include "llvm/IR/PassManager.h" #include "llvm/Pass.h" #include "llvm/Support/raw_ostream.h" @@ -44,6 +45,28 @@ PAC.preservedSet()); } +bool PostDominatorTree::dominates(const Instruction *I1, + const Instruction *I2) const { + assert(I1 && I2 && "Expecting valid I1 and I2"); + + const BasicBlock *BB1 = I1->getParent(); + const BasicBlock *BB2 = I2->getParent(); + + if (BB1 != BB2) + return Base::dominates(BB1, BB2); + + // PHINodes in a block are unordered. + if (isa(I1) && isa(I2)) + return false; + + // Loop through the basic block until we find I1 or I2. + BasicBlock::const_iterator I = BB1->begin(); + for (; &*I != I1 && &*I != I2; ++I) + /*empty*/; + + return &*I == I2; +} + bool PostDominatorTreeWrapperPass::runOnFunction(Function &F) { DT.recalculate(F); return false; diff --git a/llvm/lib/Transforms/Utils/CMakeLists.txt b/llvm/lib/Transforms/Utils/CMakeLists.txt --- a/llvm/lib/Transforms/Utils/CMakeLists.txt +++ b/llvm/lib/Transforms/Utils/CMakeLists.txt @@ -10,6 +10,7 @@ CloneFunction.cpp CloneModule.cpp CodeExtractor.cpp + CodeMoverUtils.cpp CtorUtils.cpp DemoteRegToStack.cpp EntryExitInstrumenter.cpp diff --git a/llvm/lib/Transforms/Utils/CodeMoverUtils.cpp b/llvm/lib/Transforms/Utils/CodeMoverUtils.cpp new file mode 100644 --- /dev/null +++ b/llvm/lib/Transforms/Utils/CodeMoverUtils.cpp @@ -0,0 +1,168 @@ +//===- CodeMoverUtils.cpp - CodeMover Utilities ----------------------------==// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This family of functions perform movements on basic blocks, and instructions +// contained within a function. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Utils/CodeMoverUtils.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/DependenceAnalysis.h" +#include "llvm/Analysis/PostDominators.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/Dominators.h" + +using namespace llvm; + +#define DEBUG_TYPE "codemover-utils" + +STATISTIC(HasDependences, + "Cannot move across instructions that has memory dependences"); +STATISTIC(MayThrowException, "Cannot move across instructions that may throw"); +STATISTIC(NotControlFlowEquivalent, + "Instructions are not control flow equivalent"); +STATISTIC(NotMovedPHINode, "Movement of PHINodes are not supported"); +STATISTIC(NotMovedTerminator, "Movement of Terminator are not supported"); + +bool llvm::isControlFlowEquivalent(const Instruction &I0, const Instruction &I1, + const DominatorTree &DT, + const PostDominatorTree &PDT) { + const BasicBlock *BB0 = I0.getParent(); + const BasicBlock *BB1 = I1.getParent(); + return ((DT.dominates(BB0, BB1) && PDT.dominates(BB1, BB0)) || + (PDT.dominates(BB0, BB1) && DT.dominates(BB1, BB0))); +} + +static bool reportInvalidCandidate(const Instruction &I, + llvm::Statistic &Stat) { + ++Stat; + LLVM_DEBUG(dbgs() << "Unable to move instruction: " << I << ". " + << Stat.getDesc()); + return false; +} + +/// Collect all instructions in between \p StartInst and \p EndInst, and store +/// them in \p InBetweenInsts. +static void +collectInstructionsInBetween(Instruction &StartInst, const Instruction &EndInst, + SmallPtrSetImpl &InBetweenInsts) { + assert(InBetweenInsts.empty() && "Expecting InBetweenInsts to be empty"); + + /// Get the next instructions of \p I, and push them to \p WorkList. + auto getNextInsts = [](Instruction &I, + SmallPtrSetImpl &WorkList) { + if (Instruction *NextInst = I.getNextNode()) + WorkList.insert(NextInst); + else { + assert(I.isTerminator() && "Expecting a terminator instruction"); + for (BasicBlock *Succ : successors(&I)) + WorkList.insert(&Succ->front()); + } + }; + + SmallPtrSet WorkList; + getNextInsts(StartInst, WorkList); + while (!WorkList.empty()) { + Instruction *CurInst = *WorkList.begin(); + WorkList.erase(CurInst); + + if (CurInst == &EndInst) + continue; + + if (!InBetweenInsts.insert(CurInst).second) + continue; + + getNextInsts(*CurInst, WorkList); + } +} + +bool llvm::isSafeToMoveBefore(Instruction &I, Instruction &InsertPoint, + const DominatorTree &DT, + const PostDominatorTree &PDT, + DependenceInfo &DI) { + // Cannot move itself before itself. + if (&I == &InsertPoint) + return false; + + // Not moved. + if (I.getNextNode() == &InsertPoint) + return true; + + if (isa(I) || isa(InsertPoint)) + return reportInvalidCandidate(I, NotMovedPHINode); + + if (I.isTerminator()) + return reportInvalidCandidate(I, NotMovedTerminator); + + // TODO remove this limitation. + if (!isControlFlowEquivalent(I, InsertPoint, DT, PDT)) + return reportInvalidCandidate(I, NotControlFlowEquivalent); + + // As I and InsertPoint are control flow equivalent, if I dominates + // InsertPoint, then I comes before InsertPoint. + const bool MoveForward = DT.dominates(&I, &InsertPoint); + if (MoveForward) { + // When I is being moved forward, we need to make sure the InsertPoint + // dominates every users. Or else, a user may be using an undefined I. + for (const Value *User : I.users()) + if (auto *UserInst = dyn_cast(User)) + if (!DT.dominates(&InsertPoint, UserInst)) + return false; + } else { + // When I is being moved backward, we need to make sure all its opernads + // dominates the InsertPoint. Or else, an operand may be undefined for I. + for (const Value *Op : I.operands()) + if (auto *OpInst = dyn_cast(Op)) + if (&InsertPoint == OpInst || !DT.dominates(OpInst, &InsertPoint)) + return false; + } + + Instruction &StartInst = (MoveForward ? I : InsertPoint); + Instruction &EndInst = (MoveForward ? InsertPoint : I); + SmallPtrSet InstsToCheck; + collectInstructionsInBetween(StartInst, EndInst, InstsToCheck); + if (!MoveForward) + InstsToCheck.insert(&InsertPoint); + + // Check if there exists instructions which may throw, may synchonize, or may + // never return, from I to InsertPoint. + if (!isSafeToSpeculativelyExecute(&I)) + if (std::any_of(InstsToCheck.begin(), InstsToCheck.end(), + [](Instruction *I) { + if (I->mayThrow()) + return true; + + const CallBase *CB = dyn_cast(I); + if (!CB) + return false; + if (!CB->hasFnAttr(Attribute::WillReturn)) + return true; + if (!CB->hasFnAttr(Attribute::NoSync)) + return true; + + return false; + })) { + return reportInvalidCandidate(I, MayThrowException); + } + + // Check if I has any output/flow/anti dependences with instructions from \p + // StartInst to \p EndInst. + if (std::any_of(InstsToCheck.begin(), InstsToCheck.end(), + [&DI, &I](Instruction *CurInst) { + auto DepResult = DI.depends(&I, CurInst, true); + if (DepResult && + (DepResult->isOutput() || DepResult->isFlow() || + DepResult->isAnti())) + return true; + return false; + })) + return reportInvalidCandidate(I, HasDependences); + + return true; +} diff --git a/llvm/unittests/Transforms/Utils/CMakeLists.txt b/llvm/unittests/Transforms/Utils/CMakeLists.txt --- a/llvm/unittests/Transforms/Utils/CMakeLists.txt +++ b/llvm/unittests/Transforms/Utils/CMakeLists.txt @@ -11,6 +11,7 @@ BasicBlockUtilsTest.cpp CloningTest.cpp CodeExtractorTest.cpp + CodeMoverUtilsTest.cpp FunctionComparatorTest.cpp IntegerDivisionTest.cpp LocalTest.cpp diff --git a/llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp b/llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp new file mode 100644 --- /dev/null +++ b/llvm/unittests/Transforms/Utils/CodeMoverUtilsTest.cpp @@ -0,0 +1,172 @@ +//===- CodeMoverUtils.cpp - Unit tests for CodeMoverUtils ---------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Utils/CodeMoverUtils.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/DependenceAnalysis.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/PostDominators.h" +#include "llvm/Analysis/ScalarEvolutionExpander.h" +#include "llvm/AsmParser/Parser.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/Support/SourceMgr.h" +#include "gtest/gtest.h" + +using namespace llvm; + +static std::unique_ptr parseIR(LLVMContext &C, const char *IR) { + SMDiagnostic Err; + std::unique_ptr Mod = parseAssemblyString(IR, Err, C); + if (!Mod) + Err.print("CodeMoverUtilsTests", errs()); + return Mod; +} + +static void run(Module &M, StringRef FuncName, + function_ref + Test) { + auto *F = M.getFunction(FuncName); + DominatorTree DT(*F); + PostDominatorTree PDT(*F); + TargetLibraryInfoImpl TLII; + TargetLibraryInfo TLI(TLII); + AssumptionCache AC(*F); + AliasAnalysis AA(TLI); + LoopInfo LI(DT); + ScalarEvolution SE(*F, TLI, AC, DT, LI); + DependenceInfo DI(F, &AA, &SE, &LI); + Test(*F, DT, PDT, DI); +} + +TEST(CodeMoverUtils, BasicTest) { + LLVMContext C; + + // void safecall() noexcept willreturn nosync; + // void unsafecall(); + // void foo(int * __restrict__ A, int * __restrict__ B, int * __restrict__ C, + // long N) { + // X = N / 1; + // safecall(); + // unsafecall1(); + // unsafecall2(); + // for (long i = 0; i < N; ++i) { + // A[5] = 5; + // A[i] = 0; + // B[i] = A[i]; + // C[i] = A[i]; + // A[6] = 6; + // } + // } + std::unique_ptr M = parseIR( + C, + "define void @foo(i32* noalias %A, i32* noalias %B, i32* noalias %C\n" + " , i64 %N) {\n" + "entry:\n" + " %X = sdiv i64 1, %N\n" + " call void @safecall()\n" + " %cmp1 = icmp slt i64 0, %N\n" + " call void @unsafecall1()\n" + " call void @unsafecall2()\n" + " br i1 %cmp1, label %for.body, label %for.end\n" + "for.body:\n" + " %i = phi i64 [ 0, %entry ], [ %inc, %for.body ]\n" + " %arrayidx_A5 = getelementptr inbounds i32, i32* %A, i64 5\n" + " store i32 5, i32* %arrayidx_A5, align 4\n" + " %arrayidx_A = getelementptr inbounds i32, i32* %A, i64 %i\n" + " store i32 0, i32* %arrayidx_A, align 4\n" + " %load1 = load i32, i32* %arrayidx_A, align 4\n" + " %arrayidx_B = getelementptr inbounds i32, i32* %B, i64 %i\n" + " store i32 %load1, i32* %arrayidx_B, align 4\n" + " %load2 = load i32, i32* %arrayidx_A, align 4\n" + " %arrayidx_C = getelementptr inbounds i32, i32* %C, i64 %i\n" + " store i32 %load2, i32* %arrayidx_C, align 4\n" + " %arrayidx_A6 = getelementptr inbounds i32, i32* %A, i64 6\n" + " store i32 6, i32* %arrayidx_A6, align 4\n" + " %inc = add nsw i64 %i, 1\n" + " %cmp = icmp slt i64 %inc, %N\n" + " br i1 %cmp, label %for.body, label %for.end\n" + "for.end:\n" + " ret void\n" + "}\n" + "declare void @safecall() nounwind nosync willreturn\n" + "declare void @unsafecall1()\n" + "declare void @unsafecall2()\n"); + + run(*M, "foo", + [&](Function &F, DominatorTree &DT, PostDominatorTree &PDT, + DependenceInfo &DI) { + Function::iterator FI = F.begin(); + BasicBlock *Entry = &*(FI++); + assert(Entry->getName() == "entry" && "Expecting BasicBlock entry"); + Instruction *CI_safecall = Entry->front().getNextNode(); + assert(isa(CI_safecall) && "Expecting CI_safecall to be a CallInst"); + Instruction *CI_unsafecall = CI_safecall->getNextNode()->getNextNode(); + assert(isa(CI_unsafecall) && "Expecting CI_unsafecall to be a CallInst"); + BasicBlock *ForBody = &*(FI++); + assert(ForBody->getName() == "for.body" && + "Expecting BasicBlock for.body"); + Instruction &PN = ForBody->front(); + assert(isa(PN) && "Expecting PN to be a PHINode"); + Instruction *SI_A5 = PN.getNextNode()->getNextNode(); + assert(isa(SI_A5) && + SI_A5->getOperand(1)->getName() == "arrayidx_A5" && + "Expecting store to arrayidx_A5"); + Instruction *SI = SI_A5->getNextNode()->getNextNode(); + assert(isa(SI) && + SI->getOperand(1)->getName() == "arrayidx_A" && + "Expecting store to arrayidx_A"); + Instruction *LI1 = SI->getNextNode(); + assert(LI1->getName() == "load1" && "Expecting LI1 to be load1"); + Instruction *LI2 = LI1->getNextNode()->getNextNode()->getNextNode(); + assert(LI2->getName() == "load2" && "Expecting LI2 to be load2"); + Instruction *SI_A6 = LI2->getNextNode()->getNextNode()->getNextNode()->getNextNode(); + assert(isa(SI_A6) && + SI_A6->getOperand(1)->getName() == "arrayidx_A6" && + "Expecting store to arrayidx_A6"); + + // Can move after CI_safecall, as it does not throw, not synchronize, or must return. + EXPECT_TRUE(isSafeToMoveBefore(*CI_safecall->getPrevNode(), *CI_safecall->getNextNode(), DT, PDT, DI)); + + // Cannot move CI_unsafecall, as it may throw. + EXPECT_FALSE(isSafeToMoveBefore(*CI_unsafecall->getNextNode(), *CI_unsafecall, DT, PDT, DI)); + + // Moving instruction to non control flow equivalent places are not + // supported. + EXPECT_FALSE(isSafeToMoveBefore(*SI_A5, *Entry->getTerminator(), DT, PDT, DI)); + + // Moving PHINode is not supported. + EXPECT_FALSE(isSafeToMoveBefore(PN, *PN.getPrevNode(), DT, PDT, DI)); + + // Cannot move non-PHINode before PHINode. + EXPECT_FALSE(isSafeToMoveBefore(*PN.getNextNode(), PN, DT, PDT, DI)); + + // Moving Terminator is not supported. + EXPECT_FALSE(isSafeToMoveBefore(*Entry->getTerminator(), *PN.getNextNode(), DT, + PDT, DI)); + + // Cannot move %arrayidx_A after SI, as SI is its user. + EXPECT_FALSE(isSafeToMoveBefore(*SI->getPrevNode(), *SI->getNextNode(), DT, PDT, DI)); + + // Cannot move SI before %arrayidx_A, as %arrayidx_A is its operand. + EXPECT_FALSE(isSafeToMoveBefore(*SI, *SI->getPrevNode(), DT, PDT, DI)); + + // Cannot move LI2 after SI_A6, as there is a flow dependence. + EXPECT_FALSE(isSafeToMoveBefore(*LI2, *SI_A6->getNextNode(), DT, PDT, DI)); + + // Cannot move SI after LI1, as there is a anti dependence. + EXPECT_FALSE(isSafeToMoveBefore(*SI, *LI1->getNextNode(), DT, PDT, DI)); + + // Cannot move SI_A5 after SI, as there is a output dependence. + EXPECT_FALSE(isSafeToMoveBefore(*SI_A5, *LI1, DT, PDT, DI)); + + // Can move LI2 before LI1, as there is only an input dependence. + EXPECT_TRUE(isSafeToMoveBefore(*LI2, *LI1, DT, PDT, DI)); + }); +}