[llvm] r218721 - [InstCombine] Optimize icmp-select-icmp
Chandler Carruth
chandlerc at google.com
Tue Sep 30 20:30:31 PDT 2014
It's already been 3 hours. Please do one quickly, I'm worried about the
number of commits going in after this that aren't getting sanitizer
coverage.
On Tue, Sep 30, 2014 at 8:21 PM, Gerolf Hoflehner <ghoflehner at apple.com>
wrote:
> Ok, thanks! I’ll provide a fix or back out shortly.
>
>
> On Sep 30, 2014, at 6:13 PM, Chandler Carruth <chandlerc at google.com>
> wrote:
>
> FYI, this is assert failing on build bots:
> http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux/builds/13123
>
> On Tue, Sep 30, 2014 at 5:13 PM, Gerolf Hoflehner <ghoflehner at apple.com>
> wrote:
>
>> Author: ghoflehner
>> Date: Tue Sep 30 19:13:22 2014
>> New Revision: 218721
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=218721&view=rev
>> Log:
>> [InstCombine] Optimize icmp-select-icmp
>>
>> In special cases select instructions can be eliminated by
>> replacing them with a cheaper bitwise operation even when the
>> select result is used outside its home block. The instances implemented
>> are patterns like
>> %x=icmp.eq
>> %y=select %x,%r, null
>> %z=icmp.eq|neq %y, null
>> br %z,true, false
>> ==> %x=icmp.ne
>> %y=icmp.eq %r,null
>> %z=or %x,%y
>> br %z,true,false
>> The optimization is integrated into the instruction
>> combiner and performed only when all uses of the select result can
>> be replaced by the select operand proper. For this dominator information
>> is used and dominance is now a required analysis pass in the combiner.
>> The optimization itself is iterative. The critical step is to replace the
>> select result with the non-constant select operand. So the select becomes
>> local and the combiner iteratively works out simpler code pattern and
>> eventually eliminates the select.
>>
>> rdar://17853760
>>
>>
>> Added:
>> llvm/trunk/test/Transforms/InstCombine/select-cmp-br.ll
>> Modified:
>> llvm/trunk/lib/Transforms/InstCombine/InstCombine.h
>> llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
>> llvm/trunk/test/Transforms/InstCombine/pr12338.ll
>>
>> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombine.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombine.h?rev=218721&r1=218720&r2=218721&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/InstCombine/InstCombine.h (original)
>> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombine.h Tue Sep 30
>> 19:13:22 2014
>> @@ -14,6 +14,7 @@
>> #include "llvm/Analysis/AssumptionTracker.h"
>> #include "llvm/Analysis/TargetFolder.h"
>> #include "llvm/Analysis/ValueTracking.h"
>> +#include "llvm/IR/Dominators.h"
>> #include "llvm/IR/IRBuilder.h"
>> #include "llvm/IR/InstVisitor.h"
>> #include "llvm/IR/IntrinsicInst.h"
>> @@ -98,7 +99,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombin
>> AssumptionTracker *AT;
>> const DataLayout *DL;
>> TargetLibraryInfo *TLI;
>> - DominatorTree *DT; // not required
>> + DominatorTree *DT;
>> bool MadeIRChange;
>> LibCallSimplifier *Simplifier;
>> bool MinimizeSize;
>> @@ -113,7 +114,8 @@ public:
>> BuilderTy *Builder;
>>
>> static char ID; // Pass identification, replacement for typeid
>> - InstCombiner() : FunctionPass(ID), DL(nullptr), Builder(nullptr) {
>> + InstCombiner()
>> + : FunctionPass(ID), DL(nullptr), DT(nullptr), Builder(nullptr) {
>> MinimizeSize = false;
>> initializeInstCombinerPass(*PassRegistry::getPassRegistry());
>> }
>> @@ -242,6 +244,11 @@ public:
>>
>> // visitInstruction - Specify what to return for unhandled
>> instructions...
>> Instruction *visitInstruction(Instruction &I) { return nullptr; }
>> + bool dominatesAllUses(const Instruction *DI, const Instruction *UI,
>> + const BasicBlock *DB) const;
>> + bool replacedSelectWithOperand(SelectInst *SI, const ICmpInst *Icmp,
>> + const ConstantInt *CI1,
>> + const ConstantInt *CI2);
>>
>> private:
>> bool ShouldChangeType(Type *From, Type *To) const;
>>
>> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=218721&r1=218720&r2=218721&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> (original)
>> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Tue Sep
>> 30 19:13:22 2014
>> @@ -2429,6 +2429,127 @@ static bool swapMayExposeCSEOpportunitie
>> return GlobalSwapBenefits > 0;
>> }
>>
>> +/// \brief Check that one use is in the same block as the definition and
>> all
>> +/// other uses are in blocks dominated by a given block
>> +///
>> +/// \param DI Definition
>> +/// \param UI Use
>> +/// \param DB Block that must dominate all uses of \p DI outside
>> +/// the parent block. Note there can be a use of \p DI in \p
>> DB.
>> +/// \return true when \p UI is the only use of \p DI in the parent block
>> +/// and all other uses of \p DI are in blocks dominated by \p DB.
>> +///
>> +bool InstCombiner::dominatesAllUses(const Instruction *DI,
>> + const Instruction *UI,
>> + const BasicBlock *DB) const {
>> + assert(DI && DI->getParent() == UI->getParent() &&
>> + "definition and use must be in the same block");
>> + // DominatorTree available?
>> + if (!DT)
>> + return false;
>> + for (const User *U : DI->users()) {
>> + auto *Usr = cast<Instruction>(U);
>> + if (Usr != UI && !DT->dominates(DB, Usr->getParent()))
>> + return false;
>> + }
>> + return true;
>> +}
>> +
>> +///
>> +/// true when the instruction sequence within a block is select-cmp-br.
>> +///
>> +static bool isChainSelectCmpBranch(const SelectInst *SI) {
>> + const BasicBlock *BB = SI->getParent();
>> + if (!BB)
>> + return false;
>> + auto *BI = dyn_cast_or_null<BranchInst>(BB->getTerminator());
>> + if (!BI || BI->getNumSuccessors() != 2)
>> + return false;
>> + auto *IC = dyn_cast<ICmpInst>(BI->getCondition());
>> + if (!IC || (IC->getOperand(0) != SI && IC->getOperand(1) != SI))
>> + return false;
>> + return true;
>> +}
>> +
>> +///
>> +/// \brief True when a select result is replaced by one of its operands
>> +/// in select-icmp sequence. This will eventually result in the
>> elimination
>> +/// of the select.
>> +///
>> +/// \param SI Select instruction
>> +/// \param Icmp Compare instruction
>> +/// \param CI1 'true' when first select operand is equal to RHSC of Icmp
>> +/// \param CI2 'true' when second select operand is equal to RHSC of
>> Icmp
>> +///
>> +/// Notes:
>> +/// - The replacement is global and requires dominator information
>> +/// - The caller is responsible for the actual replacement
>> +///
>> +/// Example:
>> +///
>> +/// entry:
>> +/// %4 = select i1 %3, %C* %0, %C* null
>> +/// %5 = icmp eq %C* %4, null
>> +/// br i1 %5, label %9, label %7
>> +/// ...
>> +/// ; <label>:7 ; preds = %entry
>> +/// %8 = getelementptr inbounds %C* %4, i64 0, i32 0
>> +/// ...
>> +///
>> +/// can be transformed to
>> +///
>> +/// %5 = icmp eq %C* %0, null
>> +/// %6 = select i1 %3, i1 %5, i1 true
>> +/// br i1 %6, label %9, label %7
>> +/// ...
>> +/// ; <label>:7 ; preds = %entry
>> +/// %8 = getelementptr inbounds %C* %0, i64 0, i32 0 // replace by %0!
>> +///
>> +/// Similar when the first operand of the select is a constant or/and
>> +/// the compare is for not equal rather than equal.
>> +///
>> +/// FIXME: Currently the function considers equal compares only. It
>> should be
>> +/// possbile to extend it to not equal compares also.
>> +///
>> +bool InstCombiner::replacedSelectWithOperand(SelectInst *SI,
>> + const ICmpInst *Icmp,
>> + const ConstantInt *CI1,
>> + const ConstantInt *CI2) {
>> + if (isChainSelectCmpBranch(SI) && Icmp->isEquality()) {
>> + // Code sequence is select - icmp.[eq|ne] - br
>> + unsigned ReplaceWithOpd = 0;
>> + if (CI1 && !CI1->isZero())
>> + // The first constant operand of the select and the RHS of
>> + // the compare match, so try to substitute
>> + // the select results with its second operand
>> + // Example:
>> + // %4 = select i1 %3, %C* null, %C* %0
>> + // %5 = icmp eq %C* %4, null
>> + // ==> could replace select with second operand
>> + ReplaceWithOpd = 2;
>> + else if (CI2 && !CI2->isZero())
>> + // Similar when the second operand of the select is a constant
>> + // Example:
>> + // %4 = select i1 %3, %C* %0, %C* null
>> + // %5 = icmp eq %C* %4, null
>> + // ==> could replace select with first operand
>> + ReplaceWithOpd = 1;
>> + if (ReplaceWithOpd) {
>> + // Replace select with operand on else path for EQ compares.
>> + // Replace select with operand on then path for NE compares.
>> + BasicBlock *Succ =
>> + Icmp->getPredicate() == ICmpInst::ICMP_EQ
>> + ? SI->getParent()->getTerminator()->getSuccessor(1)
>> + : SI->getParent()->getTerminator()->getSuccessor(0);
>> + if (InstCombiner::dominatesAllUses(SI, Icmp, Succ)) {
>> + SI->replaceAllUsesWith(SI->getOperand(ReplaceWithOpd));
>> + return true;
>> + }
>> + }
>> + }
>> + return false;
>> +}
>> +
>> Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
>> bool Changed = false;
>> Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
>> @@ -2885,8 +3006,21 @@ Instruction *InstCombiner::visitICmpInst
>> // fold to a constant (in which case the icmp is replaced with a
>> select
>> // which will usually simplify) or this is the only user of the
>> // select (in which case we are trading a select+icmp for a
>> simpler
>> - // select+icmp).
>> - if ((Op1 && Op2) || (LHSI->hasOneUse() && (Op1 || Op2))) {
>> + // select+icmp) or all uses of the select can be replaced based
>> on
>> + // dominance information ("Global cases").
>> + bool Transform = false;
>> + if (Op1 && Op2)
>> + Transform = true;
>> + else if (Op1 || Op2) {
>> + if (LHSI->hasOneUse())
>> + Transform = true;
>> + else
>> + // Global cases
>> + Transform = replacedSelectWithOperand(
>> + cast<SelectInst>(LHSI), &I,
>> dyn_cast_or_null<ConstantInt>(Op1),
>> + dyn_cast_or_null<ConstantInt>(Op2));
>> + }
>> + if (Transform) {
>> if (!Op1)
>> Op1 = Builder->CreateICmp(I.getPredicate(),
>> LHSI->getOperand(1),
>> RHSC, I.getName());
>>
>> Modified: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp?rev=218721&r1=218720&r2=218721&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
>> (original)
>> +++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp Tue
>> Sep 30 19:13:22 2014
>> @@ -90,6 +90,7 @@ INITIALIZE_PASS_BEGIN(InstCombiner, "ins
>> "Combine redundant instructions", false, false)
>> INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
>> INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
>> +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
>> INITIALIZE_PASS_END(InstCombiner, "instcombine",
>> "Combine redundant instructions", false, false)
>>
>> @@ -97,6 +98,8 @@ void InstCombiner::getAnalysisUsage(Anal
>> AU.setPreservesCFG();
>> AU.addRequired<AssumptionTracker>();
>> AU.addRequired<TargetLibraryInfo>();
>> + AU.addRequired<DominatorTreeWrapperPass>();
>> + AU.addPreserved<DominatorTreeWrapperPass>();
>> }
>>
>>
>> @@ -2933,12 +2936,9 @@ bool InstCombiner::runOnFunction(Functio
>> AT = &getAnalysis<AssumptionTracker>();
>> DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
>> DL = DLP ? &DLP->getDataLayout() : nullptr;
>> + DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
>> TLI = &getAnalysis<TargetLibraryInfo>();
>>
>> - DominatorTreeWrapperPass *DTWP =
>> - getAnalysisIfAvailable<DominatorTreeWrapperPass>();
>> - DT = DTWP ? &DTWP->getDomTree() : nullptr;
>> -
>> // Minimizing size?
>> MinimizeSize =
>> F.getAttributes().hasAttribute(AttributeSet::FunctionIndex,
>> Attribute::MinSize);
>>
>> Modified: llvm/trunk/test/Transforms/InstCombine/pr12338.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/pr12338.ll?rev=218721&r1=218720&r2=218721&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/InstCombine/pr12338.ll (original)
>> +++ llvm/trunk/test/Transforms/InstCombine/pr12338.ll Tue Sep 30 19:13:22
>> 2014
>> @@ -2,11 +2,11 @@
>>
>> define void @entry() nounwind {
>> entry:
>> +; CHECK: br label %for.cond
>> br label %for.cond
>>
>> for.cond:
>> %local = phi <1 x i32> [ <i32 0>, %entry ], [ %phi2, %cond.end47 ]
>> -; CHECK: sub <1 x i32> <i32 92>, %local
>> %phi3 = sub <1 x i32> zeroinitializer, %local
>> br label %cond.end
>>
>>
>> Added: llvm/trunk/test/Transforms/InstCombine/select-cmp-br.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/select-cmp-br.ll?rev=218721&view=auto
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/InstCombine/select-cmp-br.ll (added)
>> +++ llvm/trunk/test/Transforms/InstCombine/select-cmp-br.ll Tue Sep 30
>> 19:13:22 2014
>> @@ -0,0 +1,127 @@
>> +; Replace a 'select' with 'or' in 'select - cmp [eq|ne] - br' sequence
>> +; RUN: opt -instcombine -S < %s | FileCheck %s
>> +
>> +%C = type <{ %struct.S }>
>> +%struct.S = type { i64*, i32, i32 }
>> +
>> +declare void @bar(%struct.S *) #1
>> +
>> +define void @test1(%C*) {
>> +entry:
>> + %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
>> + %m = load i64** %1, align 8
>> + %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
>> + %n = load i64** %2, align 8
>> + %3 = getelementptr inbounds i64* %m, i64 9
>> + %4 = bitcast i64* %3 to i64 (%C*)**
>> + %5 = load i64 (%C*)** %4, align 8
>> + %6 = icmp eq i64* %m, %n
>> + %7 = select i1 %6, %C* %0, %C* null
>> + %8 = icmp eq %C* %7, null
>> + br i1 %8, label %12, label %10
>> +
>> +; <label>:9 ; preds = %10, %12
>> + ret void
>> +
>> +; <label>:10 ; preds = %entry
>> + %11 = getelementptr inbounds %C* %7, i64 0, i32 0
>> + tail call void @bar(%struct.S* %11)
>> + br label %9
>> +
>> +; <label>:12 ; preds = %entry
>> + %13 = tail call i64 %5(%C* %0)
>> + br label %9
>> +; CHECK-LABEL: @test1(
>> +; CHECK-NOT: select
>> +; CHECK: or
>> +}
>> +
>> +define void @test2(%C*) {
>> +entry:
>> + %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
>> + %m = load i64** %1, align 8
>> + %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
>> + %n = load i64** %2, align 8
>> + %3 = getelementptr inbounds i64* %m, i64 9
>> + %4 = bitcast i64* %3 to i64 (%C*)**
>> + %5 = load i64 (%C*)** %4, align 8
>> + %6 = icmp eq i64* %m, %n
>> + %7 = select i1 %6, %C* null, %C* %0
>> + %8 = icmp eq %C* %7, null
>> + br i1 %8, label %12, label %10
>> +
>> +; <label>:9 ; preds = %10, %12
>> + ret void
>> +
>> +; <label>:10 ; preds = %entry
>> + %11 = getelementptr inbounds %C* %7, i64 0, i32 0
>> + tail call void @bar(%struct.S* %11)
>> + br label %9
>> +
>> +; <label>:12 ; preds = %entry
>> + %13 = tail call i64 %5(%C* %0)
>> + br label %9
>> +; CHECK-LABEL: @test2(
>> +; CHECK-NOT: select
>> +; CHECK: or
>> +}
>> +
>> +define void @test3(%C*) {
>> +entry:
>> + %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
>> + %m = load i64** %1, align 8
>> + %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
>> + %n = load i64** %2, align 8
>> + %3 = getelementptr inbounds i64* %m, i64 9
>> + %4 = bitcast i64* %3 to i64 (%C*)**
>> + %5 = load i64 (%C*)** %4, align 8
>> + %6 = icmp eq i64* %m, %n
>> + %7 = select i1 %6, %C* %0, %C* null
>> + %8 = icmp ne %C* %7, null
>> + br i1 %8, label %10, label %12
>> +
>> +; <label>:9 ; preds = %10, %12
>> + ret void
>> +
>> +; <label>:10 ; preds = %entry
>> + %11 = getelementptr inbounds %C* %7, i64 0, i32 0
>> + tail call void @bar(%struct.S* %11)
>> + br label %9
>> +
>> +; <label>:12 ; preds = %entry
>> + %13 = tail call i64 %5(%C* %0)
>> + br label %9
>> +; CHECK-LABEL: @test3(
>> +; CHECK-NOT: select
>> +; CHECK: or
>> +}
>> +
>> +define void @test4(%C*) {
>> +entry:
>> + %1 = getelementptr inbounds %C* %0, i64 0, i32 0, i32 0
>> + %m = load i64** %1, align 8
>> + %2 = getelementptr inbounds %C* %0, i64 1, i32 0, i32 0
>> + %n = load i64** %2, align 8
>> + %3 = getelementptr inbounds i64* %m, i64 9
>> + %4 = bitcast i64* %3 to i64 (%C*)**
>> + %5 = load i64 (%C*)** %4, align 8
>> + %6 = icmp eq i64* %m, %n
>> + %7 = select i1 %6, %C* null, %C* %0
>> + %8 = icmp ne %C* %7, null
>> + br i1 %8, label %10, label %12
>> +
>> +; <label>:9 ; preds = %10, %12
>> + ret void
>> +
>> +; <label>:10 ; preds = %entry
>> + %11 = getelementptr inbounds %C* %7, i64 0, i32 0
>> + tail call void @bar(%struct.S* %11)
>> + br label %9
>> +
>> +; <label>:12 ; preds = %entry
>> + %13 = tail call i64 %5(%C* %0)
>> + br label %9
>> +; CHECK-LABEL: @test4(
>> +; CHECK-NOT: select
>> +; CHECK: or
>> +}
>>
>>
>> _______________________________________________
>> llvm-commits mailing list
>> llvm-commits at cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20140930/baa29b8e/attachment.html>
More information about the llvm-commits
mailing list