[llvm] r237459 - Add a speculative execution pass

Jingyue Wu jingyue at google.com
Tue May 19 13:56:48 PDT 2015


Fixed in r237724.

On Tue, May 19, 2015 at 10:12 AM, Philip Reames <listmail at philipreames.com>
wrote:

>  On 05/19/2015 10:06 AM, Jingyue Wu wrote:
>
> Sure, I'll update that. Bjarke said something about it in the review
> thread (
> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20150427/274219.html).
>
>
> That was exactly what I was looking for, thanks!
>
>
> On Tue, May 19, 2015 at 9:58 AM, Philip Reames <listmail at philipreames.com>
> wrote:
>
>> Jingyue,
>>
>> Can you spell out how this is different from the existing speculation
>> done in SimplifyCFG?  I'd really prefer to see this addressed in the
>> comments at the top of the pass.  It's something I imagine many readers are
>> going to be wondering about.
>>
>> Philip
>>
>>
>> On 05/15/2015 10:54 AM, Jingyue Wu wrote:
>>
>>> Author: jingyue
>>> Date: Fri May 15 12:54:48 2015
>>> New Revision: 237459
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=237459&view=rev
>>> Log:
>>> Add a speculative execution pass
>>>
>>> Summary:
>>> This is a pass for speculative execution of instructions for simple
>>> if-then (triangle) control flow. It's aimed at GPUs, but could perhaps be
>>> used in other contexts. Enabling this pass gives us a 1.0% geomean
>>> improvement on Google benchmark suites, with one benchmark improving 33%.
>>>
>>> Credit goes to Jingyue Wu for writing an earlier version of this pass.
>>>
>>> Patched by Bjarke Roune.
>>>
>>> Test Plan:
>>> This patch adds a set of tests in
>>> test/Transforms/SpeculativeExecution/spec.ll
>>> The pass is controlled by a flag which defaults to having the pass not
>>> run.
>>>
>>> Reviewers: eliben, dberlin, meheff, jingyue, hfinkel
>>>
>>> Reviewed By: jingyue, hfinkel
>>>
>>> Subscribers: majnemer, jholewinski, llvm-commits
>>>
>>> Differential Revision: http://reviews.llvm.org/D9360
>>>
>>> Added:
>>>      llvm/trunk/lib/Transforms/Scalar/SpeculativeExecution.cpp
>>>      llvm/trunk/test/Transforms/SpeculativeExecution/
>>>      llvm/trunk/test/Transforms/SpeculativeExecution/spec.ll
>>> Modified:
>>>      llvm/trunk/include/llvm/IR/BasicBlock.h
>>>      llvm/trunk/include/llvm/InitializePasses.h
>>>      llvm/trunk/include/llvm/LinkAllPasses.h
>>>      llvm/trunk/include/llvm/Transforms/Scalar.h
>>>      llvm/trunk/lib/IR/BasicBlock.cpp
>>>      llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
>>>      llvm/trunk/lib/Transforms/Scalar/CMakeLists.txt
>>>      llvm/trunk/lib/Transforms/Scalar/Scalar.cpp
>>>
>>> Modified: llvm/trunk/include/llvm/IR/BasicBlock.h
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/BasicBlock.h?rev=237459&r1=237458&r2=237459&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/include/llvm/IR/BasicBlock.h (original)
>>> +++ llvm/trunk/include/llvm/IR/BasicBlock.h Fri May 15 12:54:48 2015
>>> @@ -206,9 +206,19 @@ public:
>>>       return const_cast<BasicBlock*>(this)->getUniquePredecessor();
>>>     }
>>>   -  /// Return the successor of this block if it has a unique successor.
>>> -  /// Otherwise return a null pointer.  This method is analogous to
>>> -  /// getUniquePredeccessor above.
>>> +  /// \brief Return the successor of this block if it has a single
>>> successor.
>>> +  /// Otherwise return a null pointer.
>>> +  ///
>>> +  /// This method is analogous to getSinglePredecessor above.
>>> +  BasicBlock *getSingleSuccessor();
>>> +  const BasicBlock *getSingleSuccessor() const {
>>> +    return const_cast<BasicBlock*>(this)->getSingleSuccessor();
>>> +  }
>>> +
>>> +  /// \brief Return the successor of this block if it has a unique
>>> successor.
>>> +  /// Otherwise return a null pointer.
>>> +  ///
>>> +  /// This method is analogous to getUniquePredecessor above.
>>>     BasicBlock *getUniqueSuccessor();
>>>     const BasicBlock *getUniqueSuccessor() const {
>>>       return const_cast<BasicBlock*>(this)->getUniqueSuccessor();
>>>
>>> Modified: llvm/trunk/include/llvm/InitializePasses.h
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/InitializePasses.h?rev=237459&r1=237458&r2=237459&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/include/llvm/InitializePasses.h (original)
>>> +++ llvm/trunk/include/llvm/InitializePasses.h Fri May 15 12:54:48 2015
>>> @@ -256,6 +256,7 @@ void initializeSinkingPass(PassRegistry&
>>>   void initializeSeparateConstOffsetFromGEPPass(PassRegistry &);
>>>   void initializeSlotIndexesPass(PassRegistry&);
>>>   void initializeSpillPlacementPass(PassRegistry&);
>>> +void initializeSpeculativeExecutionPass(PassRegistry&);
>>>   void initializeStackProtectorPass(PassRegistry&);
>>>   void initializeStackColoringPass(PassRegistry&);
>>>   void initializeStackSlotColoringPass(PassRegistry&);
>>>
>>> Modified: llvm/trunk/include/llvm/LinkAllPasses.h
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/LinkAllPasses.h?rev=237459&r1=237458&r2=237459&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/include/llvm/LinkAllPasses.h (original)
>>> +++ llvm/trunk/include/llvm/LinkAllPasses.h Fri May 15 12:54:48 2015
>>> @@ -170,6 +170,7 @@ namespace {
>>>         (void) llvm::createPartiallyInlineLibCallsPass();
>>>         (void) llvm::createScalarizerPass();
>>>         (void) llvm::createSeparateConstOffsetFromGEPPass();
>>> +      (void) llvm::createSpeculativeExecutionPass();
>>>         (void) llvm::createRewriteSymbolsPass();
>>>         (void) llvm::createStraightLineStrengthReducePass();
>>>         (void) llvm::createMemDerefPrinter();
>>>
>>> Modified: llvm/trunk/include/llvm/Transforms/Scalar.h
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Scalar.h?rev=237459&r1=237458&r2=237459&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/include/llvm/Transforms/Scalar.h (original)
>>> +++ llvm/trunk/include/llvm/Transforms/Scalar.h Fri May 15 12:54:48 2015
>>> @@ -423,6 +423,13 @@ createSeparateConstOffsetFromGEPPass(con
>>>
>>> //===----------------------------------------------------------------------===//
>>>   //
>>> +// SpeculativeExecution - Aggressively hoist instructions to enable
>>> +// speculative execution on targets where branches are expensive.
>>> +//
>>> +FunctionPass *createSpeculativeExecutionPass();
>>> +
>>>
>>> +//===----------------------------------------------------------------------===//
>>> +//
>>>   // LoadCombine - Combine loads into bigger loads.
>>>   //
>>>   BasicBlockPass *createLoadCombinePass();
>>>
>>> Modified: llvm/trunk/lib/IR/BasicBlock.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/BasicBlock.cpp?rev=237459&r1=237458&r2=237459&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/lib/IR/BasicBlock.cpp (original)
>>> +++ llvm/trunk/lib/IR/BasicBlock.cpp Fri May 15 12:54:48 2015
>>> @@ -238,6 +238,14 @@ BasicBlock *BasicBlock::getUniquePredece
>>>     return PredBB;
>>>   }
>>>   +BasicBlock *BasicBlock::getSingleSuccessor() {
>>> +  succ_iterator SI = succ_begin(this), E = succ_end(this);
>>> +  if (SI == E) return nullptr; // no successors
>>> +  BasicBlock *TheSucc = *SI;
>>> +  ++SI;
>>> +  return (SI == E) ? TheSucc : nullptr /* multiple successors */;
>>> +}
>>> +
>>>   BasicBlock *BasicBlock::getUniqueSuccessor() {
>>>     succ_iterator SI = succ_begin(this), E = succ_end(this);
>>>     if (SI == E) return NULL; // No successors
>>>
>>> Modified: llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp?rev=237459&r1=237458&r2=237459&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp (original)
>>> +++ llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp Fri May 15
>>> 12:54:48 2015
>>> @@ -231,6 +231,7 @@ void PassManagerBuilder::populateModuleP
>>>       MPM.add(createSROAPass(/*RequiresDomTree*/ false));
>>>     else
>>>       MPM.add(createScalarReplAggregatesPass(-1, false));
>>> +
>>>     MPM.add(createEarlyCSEPass());              // Catch trivial
>>> redundancies
>>>     MPM.add(createJumpThreadingPass());         // Thread jumps.
>>>     MPM.add(createCorrelatedValuePropagationPass()); // Propagate
>>> conditionals
>>>
>>> Modified: llvm/trunk/lib/Transforms/Scalar/CMakeLists.txt
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/CMakeLists.txt?rev=237459&r1=237458&r2=237459&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/lib/Transforms/Scalar/CMakeLists.txt (original)
>>> +++ llvm/trunk/lib/Transforms/Scalar/CMakeLists.txt Fri May 15 12:54:48
>>> 2015
>>> @@ -45,6 +45,7 @@ add_llvm_library(LLVMScalarOpts
>>>     SeparateConstOffsetFromGEP.cpp
>>>     SimplifyCFGPass.cpp
>>>     Sink.cpp
>>> +  SpeculativeExecution.cpp
>>>     StraightLineStrengthReduce.cpp
>>>     StructurizeCFG.cpp
>>>     TailRecursionElimination.cpp
>>>
>>> Modified: llvm/trunk/lib/Transforms/Scalar/Scalar.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/Scalar.cpp?rev=237459&r1=237458&r2=237459&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/lib/Transforms/Scalar/Scalar.cpp (original)
>>> +++ llvm/trunk/lib/Transforms/Scalar/Scalar.cpp Fri May 15 12:54:48 2015
>>> @@ -74,6 +74,7 @@ void llvm::initializeScalarOpts(PassRegi
>>>     initializeSinkingPass(Registry);
>>>     initializeTailCallElimPass(Registry);
>>>     initializeSeparateConstOffsetFromGEPPass(Registry);
>>> +  initializeSpeculativeExecutionPass(Registry);
>>>     initializeStraightLineStrengthReducePass(Registry);
>>>     initializeLoadCombinePass(Registry);
>>>     initializePlaceBackedgeSafepointsImplPass(Registry);
>>>
>>> Added: llvm/trunk/lib/Transforms/Scalar/SpeculativeExecution.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SpeculativeExecution.cpp?rev=237459&view=auto
>>>
>>> ==============================================================================
>>> --- llvm/trunk/lib/Transforms/Scalar/SpeculativeExecution.cpp (added)
>>> +++ llvm/trunk/lib/Transforms/Scalar/SpeculativeExecution.cpp Fri May 15
>>> 12:54:48 2015
>>> @@ -0,0 +1,232 @@
>>> +//===- SpeculativeExecution.cpp ---------------------------------*- C++
>>> -*-===//
>>> +//
>>> +//                     The LLVM Compiler Infrastructure
>>> +//
>>> +// This file is distributed under the University of Illinois Open Source
>>> +// License. See LICENSE.TXT for details.
>>> +//
>>>
>>> +//===----------------------------------------------------------------------===//
>>> +//
>>> +// This pass hoists instructions to enable speculative execution on
>>> +// targets where branches are expensive. This is aimed at GPUs. It
>>> +// currently works on simple if-then and if-then-else
>>> +// patterns.
>>> +//
>>> +// Removing branches is not the only motivation for this
>>> +// pass. E.g. consider this code and assume that there is no
>>> +// addressing mode for multiplying by sizeof(*a):
>>> +//
>>> +//   if (b > 0)
>>> +//     c = a[i + 1]
>>> +//   if (d > 0)
>>> +//     e = a[i + 2]
>>> +//
>>> +// turns into
>>> +//
>>> +//   p = &a[i + 1];
>>> +//   if (b > 0)
>>> +//     c = *p;
>>> +//   q = &a[i + 2];
>>> +//   if (d > 0)
>>> +//     e = *q;
>>> +//
>>> +// which could later be optimized to
>>> +//
>>> +//   r = &a[i];
>>> +//   if (b > 0)
>>> +//     c = r[1];
>>> +//   if (d > 0)
>>> +//     e = r[2];
>>> +//
>>> +// Later passes sink back much of the speculated code that did not
>>> enable
>>> +// further optimization.
>>> +//
>>>
>>> +//===----------------------------------------------------------------------===//
>>> +
>>> +#include "llvm/ADT/SmallSet.h"
>>> +#include "llvm/Analysis/TargetTransformInfo.h"
>>> +#include "llvm/Analysis/ValueTracking.h"
>>> +#include "llvm/IR/Instructions.h"
>>> +#include "llvm/IR/Module.h"
>>> +#include "llvm/IR/Operator.h"
>>> +#include "llvm/Support/CommandLine.h"
>>> +#include "llvm/Support/Debug.h"
>>> +
>>> +using namespace llvm;
>>> +
>>> +#define DEBUG_TYPE "speculative-execution"
>>> +
>>> +// The risk that speculation will not pay off increases with the
>>> +// number of instructions speculated, so we put a limit on that.
>>> +static cl::opt<unsigned> SpecExecMaxSpeculationCost(
>>> +    "spec-exec-max-speculation-cost", cl::init(7), cl::Hidden,
>>> +    cl::desc("Speculative execution is not applied to basic blocks
>>> where "
>>> +             "the cost of the instructions to speculatively execute "
>>> +             "exceeds this limit."));
>>> +
>>> +// Speculating just a few instructions from a larger block tends not
>>> +// to be profitable and this limit prevents that. A reason for that is
>>> +// that small basic blocks are more likely to be candidates for
>>> +// further optimization.
>>> +static cl::opt<unsigned> SpecExecMaxNotHoisted(
>>> +    "spec-exec-max-not-hoisted", cl::init(5), cl::Hidden,
>>> +    cl::desc("Speculative execution is not applied to basic blocks
>>> where the "
>>> +             "number of instructions that would not be speculatively
>>> executed "
>>> +             "exceeds this limit."));
>>> +
>>> +class SpeculativeExecution : public FunctionPass {
>>> + public:
>>> +  static char ID;
>>> +  SpeculativeExecution(): FunctionPass(ID) {}
>>> +
>>> +  void getAnalysisUsage(AnalysisUsage &AU) const override;
>>> +  bool runOnFunction(Function &F) override;
>>> +
>>> + private:
>>> +  bool runOnBasicBlock(BasicBlock &B);
>>> +  bool considerHoistingFromTo(BasicBlock &FromBlock, BasicBlock
>>> &ToBlock);
>>> +
>>> +  const TargetTransformInfo *TTI = nullptr;
>>> +};
>>> +
>>> +char SpeculativeExecution::ID = 0;
>>> +INITIALIZE_PASS_BEGIN(SpeculativeExecution, "speculative-execution",
>>> +                      "Speculatively execute instructions", false,
>>> false)
>>> +INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
>>> +INITIALIZE_PASS_END(SpeculativeExecution, "speculative-execution",
>>> +                      "Speculatively execute instructions", false,
>>> false)
>>> +
>>> +void SpeculativeExecution::getAnalysisUsage(AnalysisUsage &AU) const {
>>> +  AU.addRequired<TargetTransformInfoWrapperPass>();
>>> +}
>>> +
>>> +bool SpeculativeExecution::runOnFunction(Function &F) {
>>> +  if (skipOptnoneFunction(F))
>>> +    return false;
>>> +
>>> +  TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
>>> +
>>> +  bool Changed = false;
>>> +  for (auto& B : F) {
>>> +    Changed |= runOnBasicBlock(B);
>>> +  }
>>> +  return Changed;
>>> +}
>>> +
>>> +bool SpeculativeExecution::runOnBasicBlock(BasicBlock &B) {
>>> +  BranchInst *BI = dyn_cast<BranchInst>(B.getTerminator());
>>> +  if (BI == nullptr)
>>> +    return false;
>>> +
>>> +  if (BI->getNumSuccessors() != 2)
>>> +    return false;
>>> +  BasicBlock &Succ0 = *BI->getSuccessor(0);
>>> +  BasicBlock &Succ1 = *BI->getSuccessor(1);
>>> +
>>> +  if (&B == &Succ0 || &B == &Succ1 || &Succ0 == &Succ1) {
>>> +    return false;
>>> +  }
>>> +
>>> +  // Hoist from if-then (triangle).
>>> +  if (Succ0.getSinglePredecessor() != nullptr &&
>>> +      Succ0.getSingleSuccessor() == &Succ1) {
>>> +    return considerHoistingFromTo(Succ0, B);
>>> +  }
>>> +
>>> +  // Hoist from if-else (triangle).
>>> +  if (Succ1.getSinglePredecessor() != nullptr &&
>>> +      Succ1.getSingleSuccessor() == &Succ0) {
>>> +    return considerHoistingFromTo(Succ1, B);
>>> +  }
>>> +
>>> +  // Hoist from if-then-else (diamond), but only if it is equivalent to
>>> +  // an if-else or if-then due to one of the branches doing nothing.
>>> +  if (Succ0.getSinglePredecessor() != nullptr &&
>>> +      Succ1.getSinglePredecessor() != nullptr &&
>>> +      Succ1.getSingleSuccessor() != nullptr &&
>>> +      Succ1.getSingleSuccessor() != &B &&
>>> +      Succ1.getSingleSuccessor() == Succ0.getSingleSuccessor()) {
>>> +    // If a block has only one instruction, then that is a terminator
>>> +    // instruction so that the block does nothing. This does happen.
>>> +    if (Succ1.size() == 1) // equivalent to if-then
>>> +      return considerHoistingFromTo(Succ0, B);
>>> +    if (Succ0.size() == 1) // equivalent to if-else
>>> +      return considerHoistingFromTo(Succ1, B);
>>> +  }
>>> +
>>> +  return false;
>>> +}
>>> +
>>> +static unsigned ComputeSpeculationCost(const Instruction *I,
>>> +                                       const TargetTransformInfo &TTI) {
>>> +  switch (Operator::getOpcode(I)) {
>>> +    case Instruction::GetElementPtr:
>>> +    case Instruction::Add:
>>> +    case Instruction::Mul:
>>> +    case Instruction::And:
>>> +    case Instruction::Or:
>>> +    case Instruction::Select:
>>> +    case Instruction::Shl:
>>> +    case Instruction::Sub:
>>> +    case Instruction::LShr:
>>> +    case Instruction::AShr:
>>> +    case Instruction::Xor:
>>> +    case Instruction::ZExt:
>>> +    case Instruction::SExt:
>>> +      return TTI.getUserCost(I);
>>> +
>>> +    default:
>>> +      return UINT_MAX; // Disallow anything not whitelisted.
>>> +  }
>>> +}
>>> +
>>> +bool SpeculativeExecution::considerHoistingFromTo(BasicBlock &FromBlock,
>>> +                                                  BasicBlock &ToBlock) {
>>> +  SmallSet<const Instruction *, 8> NotHoisted;
>>> +  const auto AllPrecedingUsesFromBlockHoisted = [&NotHoisted](User *U) {
>>> +    for (Value* V : U->operand_values()) {
>>> +      if (Instruction *I = dyn_cast<Instruction>(V)) {
>>> +        if (NotHoisted.count(I) > 0)
>>> +          return false;
>>> +      }
>>> +    }
>>> +    return true;
>>> +  };
>>> +
>>> +  unsigned TotalSpeculationCost = 0;
>>> +  for (auto& I : FromBlock) {
>>> +    const unsigned Cost = ComputeSpeculationCost(&I, *TTI);
>>> +    if (Cost != UINT_MAX && isSafeToSpeculativelyExecute(&I) &&
>>> +        AllPrecedingUsesFromBlockHoisted(&I)) {
>>> +      TotalSpeculationCost += Cost;
>>> +      if (TotalSpeculationCost > SpecExecMaxSpeculationCost)
>>> +        return false;  // too much to hoist
>>> +    } else {
>>> +      NotHoisted.insert(&I);
>>> +      if (NotHoisted.size() > SpecExecMaxNotHoisted)
>>> +        return false; // too much left behind
>>> +    }
>>> +  }
>>> +
>>> +  if (TotalSpeculationCost == 0)
>>> +    return false; // nothing to hoist
>>> +
>>> +  for (auto I = FromBlock.begin(); I != FromBlock.end();) {
>>> +    // We have to increment I before moving Current as moving Current
>>> +    // changes the list that I is iterating through.
>>> +    auto Current = I;
>>> +    ++I;
>>> +    if (!NotHoisted.count(Current)) {
>>> +      Current->moveBefore(ToBlock.getTerminator());
>>> +    }
>>> +  }
>>> +  return true;
>>> +}
>>> +
>>> +namespace llvm {
>>> +
>>> +FunctionPass *createSpeculativeExecutionPass() {
>>> +  return new SpeculativeExecution();
>>> +}
>>> +
>>> +}  // namespace llvm
>>>
>>> Added: llvm/trunk/test/Transforms/SpeculativeExecution/spec.ll
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SpeculativeExecution/spec.ll?rev=237459&view=auto
>>>
>>> ==============================================================================
>>> --- llvm/trunk/test/Transforms/SpeculativeExecution/spec.ll (added)
>>> +++ llvm/trunk/test/Transforms/SpeculativeExecution/spec.ll Fri May 15
>>> 12:54:48 2015
>>> @@ -0,0 +1,195 @@
>>> +; RUN: opt < %s -S -speculative-execution \
>>> +; RUN:   -spec-exec-max-speculation-cost 4 -spec-exec-max-not-hoisted 3
>>> \
>>> +; RUN:   | FileCheck %s
>>> +
>>> +target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"
>>> +
>>> +; Hoist in if-then pattern.
>>> +define void @ifThen() {
>>> +; CHECK-LABEL: @ifThen(
>>> +; CHECK: %x = add i32 2, 3
>>> +; CHECK: br i1 true
>>> +  br i1 true, label %a, label %b
>>> +; CHECK: a:
>>> +a:
>>> +  %x = add i32 2, 3
>>> +; CHECK: br label
>>> +  br label %b
>>> +; CHECK: b:
>>> +b:
>>> +; CHECK: ret void
>>> +  ret void
>>> +}
>>> +
>>> +; Hoist in if-else pattern.
>>> +define void @ifElse() {
>>> +; CHECK-LABEL: @ifElse(
>>> +; CHECK: %x = add i32 2, 3
>>> +; CHECK: br i1 true
>>> +  br i1 true, label %b, label %a
>>> +; CHECK: a:
>>> +a:
>>> +  %x = add i32 2, 3
>>> +; CHECK: br label
>>> +  br label %b
>>> +; CHECK: b:
>>> +b:
>>> +; CHECK: ret void
>>> +  ret void
>>> +}
>>> +
>>> +; Hoist in if-then-else pattern if it is equivalent to if-then.
>>> +define void @ifElseThenAsIfThen() {
>>> +; CHECK-LABEL: @ifElseThenAsIfThen(
>>> +; CHECK: %x = add i32 2, 3
>>> +; CHECK: br
>>> +  br i1 true, label %a, label %b
>>> +; CHECK: a:
>>> +a:
>>> +  %x = add i32 2, 3
>>> +; CHECK: br label
>>> +  br label %c
>>> +; CHECK: b:
>>> +b:
>>> +  br label %c
>>> +; CHECK: c
>>> +c:
>>> +  ret void
>>> +}
>>> +
>>> +; Hoist in if-then-else pattern if it is equivalent to if-else.
>>> +define void @ifElseThenAsIfElse() {
>>> +; CHECK-LABEL: @ifElseThenAsIfElse(
>>> +; CHECK: %x = add i32 2, 3
>>> +; CHECK: br
>>> +  br i1 true, label %b, label %a
>>> +; CHECK: a:
>>> +a:
>>> +  %x = add i32 2, 3
>>> +; CHECK: br label
>>> +  br label %c
>>> +; CHECK: b:
>>> +b:
>>> +  br label %c
>>> +; CHECK: c
>>> +c:
>>> +  ret void
>>> +}
>>> +
>>> +; Do not hoist if-then-else pattern if it is not equivalent to if-then
>>> +; or if-else.
>>> +define void @ifElseThen() {
>>> +; CHECK-LABEL: @ifElseThen(
>>> +; CHECK: br
>>> +  br i1 true, label %a, label %b
>>> +; CHECK: a:
>>> +a:
>>> +; CHECK: %x = add
>>> +  %x = add i32 2, 3
>>> +; CHECK: br label
>>> +  br label %c
>>> +; CHECK: b:
>>> +b:
>>> +; CHECK: %y = add
>>> +  %y = add i32 2, 3
>>> +  br label %c
>>> +; CHECK: c
>>> +c:
>>> +  ret void
>>> +}
>>> +
>>> +; Do not hoist loads and do not hoist an instruction past a definition
>>> of
>>> +; an operand.
>>> +define void @doNotHoistPastDef() {
>>> +; CHECK-LABEL: @doNotHoistPastDef(
>>> +  br i1 true, label %b, label %a
>>> +; CHECK-NOT: load
>>> +; CHECK-NOT: add
>>> +; CHECK: a:
>>> +a:
>>> +; CHECK: %def = load
>>> +  %def = load i32, i32* null
>>> +; CHECK: %use = add
>>> +  %use = add i32 %def, 0
>>> +  br label %b
>>> +; CHECK: b:
>>> +b:
>>> +  ret void
>>> +}
>>> +
>>> +; Case with nothing to speculate.
>>> +define void @nothingToSpeculate() {
>>> +; CHECK-LABEL: @nothingToSpeculate(
>>> +  br i1 true, label %b, label %a
>>> +; CHECK: a:
>>> +a:
>>> +; CHECK: %def = load
>>> +  %def = load i32, i32* null
>>> +  br label %b
>>> +; CHECK: b:
>>> +b:
>>> +  ret void
>>> +}
>>> +
>>> +; Still hoist if an operand is defined before the block or is itself
>>> hoisted.
>>> +define void @hoistIfNotPastDef() {
>>> +; CHECK-LABEL: @hoistIfNotPastDef(
>>> +; CHECK: %x = load
>>> +  %x = load i32, i32* null
>>> +; CHECK: %y = add i32 %x, 1
>>> +; CHECK: %z = add i32 %y, 1
>>> +; CHECK: br
>>> +  br i1 true, label %b, label %a
>>> +; CHECK: a:
>>> +a:
>>> +  %y = add i32 %x, 1
>>> +  %z = add i32 %y, 1
>>> +  br label %b
>>> +; CHECK: b:
>>> +b:
>>> +  ret void
>>> +}
>>> +
>>> +; Do not hoist if the speculation cost is too high.
>>> +define void @costTooHigh() {
>>> +; CHECK-LABEL: @costTooHigh(
>>> +; CHECK: br
>>> +  br i1 true, label %b, label %a
>>> +; CHECK: a:
>>> +a:
>>> +; CHECK: %r1 = add
>>> +  %r1 = add i32 1, 1
>>> +; CHECK: %r2 = add
>>> +  %r2 = add i32 1, 1
>>> +; CHECK: %r3 = add
>>> +  %r3 = add i32 1, 1
>>> +; CHECK: %r4 = add
>>> +  %r4 = add i32 1, 1
>>> +; CHECK: %r5 = add
>>> +  %r5 = add i32 1, 1
>>> +  br label %b
>>> +; CHECK: b:
>>> +b:
>>> +  ret void
>>> +}
>>> +
>>> +; Do not hoist if too many instructions are left behind.
>>> +define void @tooMuchLeftBehind() {
>>> +; CHECK-LABEL: @tooMuchLeftBehind(
>>> +; CHECK: br
>>> +  br i1 true, label %b, label %a
>>> +; CHECK: a:
>>> +a:
>>> +; CHECK: %x = load
>>> +  %x = load i32, i32* null
>>> +; CHECK: %r1 = add
>>> +  %r1 = add i32 %x, 1
>>> +; CHECK: %r2 = add
>>> +  %r2 = add i32 %x, 1
>>> +; CHECK: %r3 = add
>>> +  %r3 = add i32 %x, 1
>>> +  br label %b
>>> +; CHECK: b:
>>> +b:
>>> +  ret void
>>> +}
>>>
>>>
>>> _______________________________________________
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>>> llvm-commits at cs.uiuc.edu
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>>>
>>
>>
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