[llvm] r237459 - Add a speculative execution pass
Jingyue Wu
jingyue at google.com
Tue May 19 10:06:50 PDT 2015
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
).
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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