lib/Analysis/MustExecute.cpp - SwiftShader - Git at Google

 //===- MustExecute.cpp - Printer for isGuaranteedToExecute ----------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/Analysis/MustExecute.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/Passes.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/AssemblyAnnotationWriter.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FormattedStream.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;

 /// Computes loop safety information, checks loop body & header
 /// for the possibility of may throw exception.
 ///
 void llvm::computeLoopSafetyInfo(LoopSafetyInfo *SafetyInfo, Loop *CurLoop) {
   assert(CurLoop != nullptr && "CurLoop can't be null");
   BasicBlock *Header = CurLoop->getHeader();
   // Setting default safety values.
   SafetyInfo->MayThrow = false;
   SafetyInfo->HeaderMayThrow = false;
   // Iterate over header and compute safety info.
   SafetyInfo->HeaderMayThrow =
     !isGuaranteedToTransferExecutionToSuccessor(Header);

   SafetyInfo->MayThrow = SafetyInfo->HeaderMayThrow;
   // Iterate over loop instructions and compute safety info.
   // Skip header as it has been computed and stored in HeaderMayThrow.
   // The first block in loopinfo.Blocks is guaranteed to be the header.
   assert(Header == *CurLoop->getBlocks().begin() &&
          "First block must be header");
   for (Loop::block_iterator BB = std::next(CurLoop->block_begin()),
                             BBE = CurLoop->block_end();
        (BB != BBE) && !SafetyInfo->MayThrow; ++BB)
     SafetyInfo->MayThrow |=
       !isGuaranteedToTransferExecutionToSuccessor(*BB);

   // Compute funclet colors if we might sink/hoist in a function with a funclet
   // personality routine.
   Function *Fn = CurLoop->getHeader()->getParent();
   if (Fn->hasPersonalityFn())
     if (Constant *PersonalityFn = Fn->getPersonalityFn())
       if (isScopedEHPersonality(classifyEHPersonality(PersonalityFn)))
         SafetyInfo->BlockColors = colorEHFunclets(*Fn);
 }

 /// Return true if we can prove that the given ExitBlock is not reached on the
 /// first iteration of the given loop.  That is, the backedge of the loop must
 /// be executed before the ExitBlock is executed in any dynamic execution trace.
 static bool CanProveNotTakenFirstIteration(BasicBlock *ExitBlock,
                                            const DominatorTree *DT,
                                            const Loop *CurLoop) {
   auto *CondExitBlock = ExitBlock->getSinglePredecessor();
   if (!CondExitBlock)
     // expect unique exits
     return false;
   assert(CurLoop->contains(CondExitBlock) && "meaning of exit block");
   auto *BI = dyn_cast<BranchInst>(CondExitBlock->getTerminator());
   if (!BI || !BI->isConditional())
     return false;
   // If condition is constant and false leads to ExitBlock then we always
   // execute the true branch.
   if (auto *Cond = dyn_cast<ConstantInt>(BI->getCondition()))
     return BI->getSuccessor(Cond->getZExtValue() ? 1 : 0) == ExitBlock;
   auto *Cond = dyn_cast<CmpInst>(BI->getCondition());
   if (!Cond)
     return false;
   // todo: this would be a lot more powerful if we used scev, but all the
   // plumbing is currently missing to pass a pointer in from the pass
   // Check for cmp (phi [x, preheader] ...), y where (pred x, y is known
   auto *LHS = dyn_cast<PHINode>(Cond->getOperand(0));
   auto *RHS = Cond->getOperand(1);
   if (!LHS || LHS->getParent() != CurLoop->getHeader())
     return false;
   auto DL = ExitBlock->getModule()->getDataLayout();
   auto *IVStart = LHS->getIncomingValueForBlock(CurLoop->getLoopPreheader());
   auto *SimpleValOrNull = SimplifyCmpInst(Cond->getPredicate(),
                                           IVStart, RHS,
                                           {DL, /*TLI*/ nullptr,
                                               DT, /*AC*/ nullptr, BI});
   auto *SimpleCst = dyn_cast_or_null<Constant>(SimpleValOrNull);
   if (!SimpleCst)
     return false;
   if (ExitBlock == BI->getSuccessor(0))
     return SimpleCst->isZeroValue();
   assert(ExitBlock == BI->getSuccessor(1) && "implied by above");
   return SimpleCst->isAllOnesValue();
 }

 /// Returns true if the instruction in a loop is guaranteed to execute at least
 /// once.
 bool llvm::isGuaranteedToExecute(const Instruction &Inst,
                                  const DominatorTree *DT, const Loop *CurLoop,
                                  const LoopSafetyInfo *SafetyInfo) {
   // We have to check to make sure that the instruction dominates all
   // of the exit blocks.  If it doesn't, then there is a path out of the loop
   // which does not execute this instruction, so we can't hoist it.

   // If the instruction is in the header block for the loop (which is very
   // common), it is always guaranteed to dominate the exit blocks.  Since this
   // is a common case, and can save some work, check it now.
   if (Inst.getParent() == CurLoop->getHeader())
     // If there's a throw in the header block, we can't guarantee we'll reach
     // Inst unless we can prove that Inst comes before the potential implicit
     // exit.  At the moment, we use a (cheap) hack for the common case where
     // the instruction of interest is the first one in the block.
     return !SafetyInfo->HeaderMayThrow ||
       Inst.getParent()->getFirstNonPHIOrDbg() == &Inst;

   // Somewhere in this loop there is an instruction which may throw and make us
   // exit the loop.
   if (SafetyInfo->MayThrow)
     return false;

   // Note: There are two styles of reasoning intermixed below for
   // implementation efficiency reasons.  They are:
   // 1) If we can prove that the instruction dominates all exit blocks, then we
   // know the instruction must have executed on *some* iteration before we
   // exit.  We do not prove *which* iteration the instruction must execute on.
   // 2) If we can prove that the instruction dominates the latch and all exits
   // which might be taken on the first iteration, we know the instruction must
   // execute on the first iteration.  This second style allows a conditional
   // exit before the instruction of interest which is provably not taken on the
   // first iteration.  This is a quite common case for range check like
   // patterns.  TODO: support loops with multiple latches.

   const bool InstDominatesLatch =
     CurLoop->getLoopLatch() != nullptr &&
     DT->dominates(Inst.getParent(), CurLoop->getLoopLatch());

   // Get the exit blocks for the current loop.
   SmallVector<BasicBlock *, 8> ExitBlocks;
   CurLoop->getExitBlocks(ExitBlocks);

   // Verify that the block dominates each of the exit blocks of the loop.
   for (BasicBlock *ExitBlock : ExitBlocks)
     if (!DT->dominates(Inst.getParent(), ExitBlock))
       if (!InstDominatesLatch ||
           !CanProveNotTakenFirstIteration(ExitBlock, DT, CurLoop))
         return false;

   // As a degenerate case, if the loop is statically infinite then we haven't
   // proven anything since there are no exit blocks.
   if (ExitBlocks.empty())
     return false;

   // FIXME: In general, we have to prove that the loop isn't an infinite loop.
   // See http::llvm.org/PR24078 .  (The "ExitBlocks.empty()" check above is
   // just a special case of this.)
   return true;
 }


 namespace {
   struct MustExecutePrinter : public FunctionPass {

     static char ID; // Pass identification, replacement for typeid
     MustExecutePrinter() : FunctionPass(ID) {
       initializeMustExecutePrinterPass(*PassRegistry::getPassRegistry());
     }
     void getAnalysisUsage(AnalysisUsage &AU) const override {
       AU.setPreservesAll();
       AU.addRequired<DominatorTreeWrapperPass>();
       AU.addRequired<LoopInfoWrapperPass>();
     }
     bool runOnFunction(Function &F) override;
   };
 }

 char MustExecutePrinter::ID = 0;
 INITIALIZE_PASS_BEGIN(MustExecutePrinter, "print-mustexecute",
                       "Instructions which execute on loop entry", false, true)
 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
 INITIALIZE_PASS_END(MustExecutePrinter, "print-mustexecute",
                     "Instructions which execute on loop entry", false, true)

 FunctionPass *llvm::createMustExecutePrinter() {
   return new MustExecutePrinter();
 }

 static bool isMustExecuteIn(const Instruction &I, Loop *L, DominatorTree *DT) {
   // TODO: merge these two routines.  For the moment, we display the best
   // result obtained by *either* implementation.  This is a bit unfair since no
   // caller actually gets the full power at the moment.
   LoopSafetyInfo LSI;
   computeLoopSafetyInfo(&LSI, L);
   return isGuaranteedToExecute(I, DT, L, &LSI) ||
     isGuaranteedToExecuteForEveryIteration(&I, L);
 }

 namespace {
 /// An assembly annotator class to print must execute information in
 /// comments.
 class MustExecuteAnnotatedWriter : public AssemblyAnnotationWriter {
   DenseMap<const Value*, SmallVector<Loop*, 4> > MustExec;

 public:
   MustExecuteAnnotatedWriter(const Function &F,
                              DominatorTree &DT, LoopInfo &LI) {
     for (auto &I: instructions(F)) {
       Loop *L = LI.getLoopFor(I.getParent());
       while (L) {
         if (isMustExecuteIn(I, L, &DT)) {
           MustExec[&I].push_back(L);
         }
         L = L->getParentLoop();
       };
     }
   }
   MustExecuteAnnotatedWriter(const Module &M,
                              DominatorTree &DT, LoopInfo &LI) {
     for (auto &F : M)
     for (auto &I: instructions(F)) {
       Loop *L = LI.getLoopFor(I.getParent());
       while (L) {
         if (isMustExecuteIn(I, L, &DT)) {
           MustExec[&I].push_back(L);
         }
         L = L->getParentLoop();
       };
     }
   }


   void printInfoComment(const Value &V, formatted_raw_ostream &OS) override {
     if (!MustExec.count(&V))
       return;

     const auto &Loops = MustExec.lookup(&V);
     const auto NumLoops = Loops.size();
     if (NumLoops > 1)
       OS << " ; (mustexec in " << NumLoops << " loops: ";
     else
       OS << " ; (mustexec in: ";

     bool first = true;
     for (const Loop *L : Loops) {
       if (!first)
         OS << ", ";
       first = false;
       OS << L->getHeader()->getName();
     }
     OS << ")";
   }
 };
 } // namespace

 bool MustExecutePrinter::runOnFunction(Function &F) {
   auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
   auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();

   MustExecuteAnnotatedWriter Writer(F, DT, LI);
   F.print(dbgs(), &Writer);

   return false;
 }
	//===- MustExecute.cpp - Printer for isGuaranteedToExecute ----------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/Analysis/MustExecute.h"
	#include "llvm/Analysis/InstructionSimplify.h"
	#include "llvm/Analysis/LoopInfo.h"
	#include "llvm/Analysis/Passes.h"
	#include "llvm/Analysis/ValueTracking.h"
	#include "llvm/IR/AssemblyAnnotationWriter.h"
	#include "llvm/IR/DataLayout.h"
	#include "llvm/IR/InstIterator.h"
	#include "llvm/IR/LLVMContext.h"
	#include "llvm/IR/Module.h"
	#include "llvm/Support/ErrorHandling.h"
	#include "llvm/Support/FormattedStream.h"
	#include "llvm/Support/raw_ostream.h"
	using namespace llvm;

	/// Computes loop safety information, checks loop body & header
	/// for the possibility of may throw exception.
	///
	void llvm::computeLoopSafetyInfo(LoopSafetyInfo SafetyInfo, Loop CurLoop) {
	assert(CurLoop != nullptr && "CurLoop can't be null");
	BasicBlock *Header = CurLoop->getHeader();
	// Setting default safety values.
	SafetyInfo->MayThrow = false;
	SafetyInfo->HeaderMayThrow = false;
	// Iterate over header and compute safety info.
	SafetyInfo->HeaderMayThrow =
	!isGuaranteedToTransferExecutionToSuccessor(Header);

	SafetyInfo->MayThrow = SafetyInfo->HeaderMayThrow;
	// Iterate over loop instructions and compute safety info.
	// Skip header as it has been computed and stored in HeaderMayThrow.
	// The first block in loopinfo.Blocks is guaranteed to be the header.
	assert(Header == *CurLoop->getBlocks().begin() &&
	"First block must be header");
	for (Loop::block_iterator BB = std::next(CurLoop->block_begin()),
	BBE = CurLoop->block_end();
	(BB != BBE) && !SafetyInfo->MayThrow; ++BB)
	SafetyInfo->MayThrow \|=
	!isGuaranteedToTransferExecutionToSuccessor(*BB);

	// Compute funclet colors if we might sink/hoist in a function with a funclet
	// personality routine.
	Function *Fn = CurLoop->getHeader()->getParent();
	if (Fn->hasPersonalityFn())
	if (Constant *PersonalityFn = Fn->getPersonalityFn())
	if (isScopedEHPersonality(classifyEHPersonality(PersonalityFn)))
	SafetyInfo->BlockColors = colorEHFunclets(*Fn);
	}

	/// Return true if we can prove that the given ExitBlock is not reached on the
	/// first iteration of the given loop. That is, the backedge of the loop must
	/// be executed before the ExitBlock is executed in any dynamic execution trace.
	static bool CanProveNotTakenFirstIteration(BasicBlock *ExitBlock,
	const DominatorTree *DT,
	const Loop *CurLoop) {
	auto *CondExitBlock = ExitBlock->getSinglePredecessor();
	if (!CondExitBlock)
	// expect unique exits
	return false;
	assert(CurLoop->contains(CondExitBlock) && "meaning of exit block");
	auto *BI = dyn_cast<BranchInst>(CondExitBlock->getTerminator());
	if (!BI \|\| !BI->isConditional())
	return false;
	// If condition is constant and false leads to ExitBlock then we always
	// execute the true branch.
	if (auto *Cond = dyn_cast<ConstantInt>(BI->getCondition()))
	return BI->getSuccessor(Cond->getZExtValue() ? 1 : 0) == ExitBlock;
	auto *Cond = dyn_cast<CmpInst>(BI->getCondition());
	if (!Cond)
	return false;
	// todo: this would be a lot more powerful if we used scev, but all the
	// plumbing is currently missing to pass a pointer in from the pass
	// Check for cmp (phi [x, preheader] ...), y where (pred x, y is known
	auto *LHS = dyn_cast<PHINode>(Cond->getOperand(0));
	auto *RHS = Cond->getOperand(1);
	if (!LHS \|\| LHS->getParent() != CurLoop->getHeader())
	return false;
	auto DL = ExitBlock->getModule()->getDataLayout();
	auto *IVStart = LHS->getIncomingValueForBlock(CurLoop->getLoopPreheader());
	auto *SimpleValOrNull = SimplifyCmpInst(Cond->getPredicate(),
	IVStart, RHS,
	{DL, /TLI/ nullptr,
	DT, /AC/ nullptr, BI});
	auto *SimpleCst = dyn_cast_or_null<Constant>(SimpleValOrNull);
	if (!SimpleCst)
	return false;
	if (ExitBlock == BI->getSuccessor(0))
	return SimpleCst->isZeroValue();
	assert(ExitBlock == BI->getSuccessor(1) && "implied by above");
	return SimpleCst->isAllOnesValue();
	}

	/// Returns true if the instruction in a loop is guaranteed to execute at least
	/// once.
	bool llvm::isGuaranteedToExecute(const Instruction &Inst,
	const DominatorTree DT, const Loop CurLoop,
	const LoopSafetyInfo *SafetyInfo) {
	// We have to check to make sure that the instruction dominates all
	// of the exit blocks. If it doesn't, then there is a path out of the loop
	// which does not execute this instruction, so we can't hoist it.

	// If the instruction is in the header block for the loop (which is very
	// common), it is always guaranteed to dominate the exit blocks. Since this
	// is a common case, and can save some work, check it now.
	if (Inst.getParent() == CurLoop->getHeader())
	// If there's a throw in the header block, we can't guarantee we'll reach
	// Inst unless we can prove that Inst comes before the potential implicit
	// exit. At the moment, we use a (cheap) hack for the common case where
	// the instruction of interest is the first one in the block.
	return !SafetyInfo->HeaderMayThrow \|\|
	Inst.getParent()->getFirstNonPHIOrDbg() == &Inst;

	// Somewhere in this loop there is an instruction which may throw and make us
	// exit the loop.
	if (SafetyInfo->MayThrow)
	return false;

	// Note: There are two styles of reasoning intermixed below for
	// implementation efficiency reasons. They are:
	// 1) If we can prove that the instruction dominates all exit blocks, then we
	// know the instruction must have executed on some iteration before we
	// exit. We do not prove which iteration the instruction must execute on.
	// 2) If we can prove that the instruction dominates the latch and all exits
	// which might be taken on the first iteration, we know the instruction must
	// execute on the first iteration. This second style allows a conditional
	// exit before the instruction of interest which is provably not taken on the
	// first iteration. This is a quite common case for range check like
	// patterns. TODO: support loops with multiple latches.

	const bool InstDominatesLatch =
	CurLoop->getLoopLatch() != nullptr &&
	DT->dominates(Inst.getParent(), CurLoop->getLoopLatch());

	// Get the exit blocks for the current loop.
	SmallVector<BasicBlock *, 8> ExitBlocks;
	CurLoop->getExitBlocks(ExitBlocks);

	// Verify that the block dominates each of the exit blocks of the loop.
	for (BasicBlock *ExitBlock : ExitBlocks)
	if (!DT->dominates(Inst.getParent(), ExitBlock))
	if (!InstDominatesLatch \|\|
	!CanProveNotTakenFirstIteration(ExitBlock, DT, CurLoop))
	return false;

	// As a degenerate case, if the loop is statically infinite then we haven't
	// proven anything since there are no exit blocks.
	if (ExitBlocks.empty())
	return false;

	// FIXME: In general, we have to prove that the loop isn't an infinite loop.
	// See http::llvm.org/PR24078 . (The "ExitBlocks.empty()" check above is
	// just a special case of this.)
	return true;
	}


	namespace {
	struct MustExecutePrinter : public FunctionPass {

	static char ID; // Pass identification, replacement for typeid
	MustExecutePrinter() : FunctionPass(ID) {
	initializeMustExecutePrinterPass(*PassRegistry::getPassRegistry());
	}
	void getAnalysisUsage(AnalysisUsage &AU) const override {
	AU.setPreservesAll();
	AU.addRequired<DominatorTreeWrapperPass>();
	AU.addRequired<LoopInfoWrapperPass>();
	}
	bool runOnFunction(Function &F) override;
	};
	}

	char MustExecutePrinter::ID = 0;
	INITIALIZE_PASS_BEGIN(MustExecutePrinter, "print-mustexecute",
	"Instructions which execute on loop entry", false, true)
	INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
	INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
	INITIALIZE_PASS_END(MustExecutePrinter, "print-mustexecute",
	"Instructions which execute on loop entry", false, true)

	FunctionPass *llvm::createMustExecutePrinter() {
	return new MustExecutePrinter();
	}

	static bool isMustExecuteIn(const Instruction &I, Loop L, DominatorTree DT) {
	// TODO: merge these two routines. For the moment, we display the best
	// result obtained by either implementation. This is a bit unfair since no
	// caller actually gets the full power at the moment.
	LoopSafetyInfo LSI;
	computeLoopSafetyInfo(&LSI, L);
	return isGuaranteedToExecute(I, DT, L, &LSI) \|\|
	isGuaranteedToExecuteForEveryIteration(&I, L);
	}

	namespace {
	/// An assembly annotator class to print must execute information in
	/// comments.
	class MustExecuteAnnotatedWriter : public AssemblyAnnotationWriter {
	DenseMap<const Value, SmallVector<Loop, 4> > MustExec;

	public:
	MustExecuteAnnotatedWriter(const Function &F,
	DominatorTree &DT, LoopInfo &LI) {
	for (auto &I: instructions(F)) {
	Loop *L = LI.getLoopFor(I.getParent());
	while (L) {
	if (isMustExecuteIn(I, L, &DT)) {
	MustExec[&I].push_back(L);
	}
	L = L->getParentLoop();
	};
	}
	}
	MustExecuteAnnotatedWriter(const Module &M,
	DominatorTree &DT, LoopInfo &LI) {
	for (auto &F : M)
	for (auto &I: instructions(F)) {
	Loop *L = LI.getLoopFor(I.getParent());
	while (L) {
	if (isMustExecuteIn(I, L, &DT)) {
	MustExec[&I].push_back(L);
	}
	L = L->getParentLoop();
	};
	}
	}


	void printInfoComment(const Value &V, formatted_raw_ostream &OS) override {
	if (!MustExec.count(&V))
	return;

	const auto &Loops = MustExec.lookup(&V);
	const auto NumLoops = Loops.size();
	if (NumLoops > 1)
	OS << " ; (mustexec in " << NumLoops << " loops: ";
	else
	OS << " ; (mustexec in: ";

	bool first = true;
	for (const Loop *L : Loops) {
	if (!first)
	OS << ", ";
	first = false;
	OS << L->getHeader()->getName();
	}
	OS << ")";
	}
	};
	} // namespace

	bool MustExecutePrinter::runOnFunction(Function &F) {
	auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
	auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();

	MustExecuteAnnotatedWriter Writer(F, DT, LI);
	F.print(dbgs(), &Writer);

	return false;
	}