[llvm] r246243 - Constant propagation after hiting llvm.assume
Piotr Padlewski via llvm-commits
llvm-commits at lists.llvm.org
Fri Aug 28 16:44:53 PDT 2015
replaceDominatedUsesWith works across different BBs, and I wanted to have
something that will replace all the non const variables with const ones
after hiting @llvm.assume.
Piotr
On Fri, Aug 28, 2015 at 9:54 AM, Philip Reames <listmail at philipreames.com>
wrote:
> Piotr,
>
> I'm a bit confused by the need for the ReplaceWithConstMap variable in
> this patch. Wouldn't simply calling replaceDominatedUsesWith be
> sufficient? Is there a reason to prefer the BB local variable?
>
> Philip
>
>
>
> On 08/27/2015 06:01 PM, Piotr Padlewski via llvm-commits wrote:
>
>> Author: prazek
>> Date: Thu Aug 27 20:01:57 2015
>> New Revision: 246243
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=246243&view=rev
>> Log:
>> Constant propagation after hiting llvm.assume
>>
>> After hitting @llvm.assume(X) we can:
>> - propagate equality that X == true
>> - if X is icmp/fcmp (with eq operation), and one of operand
>> is constant we can change all variables with constants in the same
>> BasicBlock
>>
>> http://reviews.llvm.org/D11918
>>
>> Added:
>> llvm/trunk/test/Transforms/GVN/assume-equal.ll
>> Modified:
>> llvm/trunk/lib/Transforms/Scalar/GVN.cpp
>>
>> Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=246243&r1=246242&r2=246243&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Thu Aug 27 20:01:57 2015
>> @@ -608,6 +608,10 @@ namespace {
>> DenseMap<uint32_t, LeaderTableEntry> LeaderTable;
>> BumpPtrAllocator TableAllocator;
>> + // Block-local map of equivalent values to their leader, does not
>> + // propagate to any successors. Entries added mid-block are applied
>> + // to the remaining instructions in the block.
>> + SmallMapVector<llvm::Value *, llvm::Constant *, 4>
>> ReplaceWithConstMap;
>> SmallVector<Instruction*, 8> InstrsToErase;
>> typedef SmallVector<NonLocalDepResult, 64> LoadDepVect;
>> @@ -699,6 +703,7 @@ namespace {
>> // Helper functions of redundant load elimination
>> bool processLoad(LoadInst *L);
>> bool processNonLocalLoad(LoadInst *L);
>> + bool processAssumeIntrinsic(IntrinsicInst *II);
>> void AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps,
>> AvailValInBlkVect &ValuesPerBlock,
>> UnavailBlkVect &UnavailableBlocks);
>> @@ -719,6 +724,7 @@ namespace {
>> void verifyRemoved(const Instruction *I) const;
>> bool splitCriticalEdges();
>> BasicBlock *splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ);
>> + bool replaceOperandsWithConsts(Instruction *I) const;
>> bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge
>> &Root);
>> bool processFoldableCondBr(BranchInst *BI);
>> void addDeadBlock(BasicBlock *BB);
>> @@ -1760,6 +1766,38 @@ bool GVN::processNonLocalLoad(LoadInst *
>> return PerformLoadPRE(LI, ValuesPerBlock, UnavailableBlocks);
>> }
>> +bool GVN::processAssumeIntrinsic(IntrinsicInst *IntrinsicI) {
>> + assert(IntrinsicI->getIntrinsicID() == Intrinsic::assume &&
>> + "This function can only be called with llvm.assume intrinsic");
>> + Value *V = IntrinsicI->getArgOperand(0);
>> + Constant *True = ConstantInt::getTrue(V->getContext());
>> + bool Changed = false;
>> + for (BasicBlock *Successor : successors(IntrinsicI->getParent())) {
>> + BasicBlockEdge Edge(IntrinsicI->getParent(), Successor);
>> +
>> + // This property is only true in dominated successors,
>> propagateEquality
>> + // will check dominance for us.
>> + Changed |= propagateEquality(V, True, Edge);
>> + }
>> +
>> + if (auto *CmpI = dyn_cast<CmpInst>(V)) {
>> + if (CmpI->getPredicate() == CmpInst::Predicate::ICMP_EQ ||
>> + CmpI->getPredicate() == CmpInst::Predicate::FCMP_OEQ ||
>> + (CmpI->getPredicate() == CmpInst::Predicate::FCMP_UEQ &&
>> + CmpI->getFastMathFlags().noNaNs())) {
>> + Value *CmpLHS = CmpI->getOperand(0);
>> + Value *CmpRHS = CmpI->getOperand(1);
>> + if (isa<Constant>(CmpLHS))
>> + std::swap(CmpLHS, CmpRHS);
>> + auto *RHSConst = dyn_cast<Constant>(CmpRHS);
>> +
>> + // If only one operand is constant.
>> + if (RHSConst != nullptr && !isa<Constant>(CmpLHS))
>> + ReplaceWithConstMap[CmpLHS] = RHSConst;
>> + }
>> + }
>> + return Changed;
>> +}
>> static void patchReplacementInstruction(Instruction *I, Value *Repl) {
>> // Patch the replacement so that it is not more restrictive than the
>> value
>> @@ -2032,6 +2070,21 @@ static bool isOnlyReachableViaThisEdge(c
>> return Pred != nullptr;
>> }
>> +// Tries to replace instruction with const, using information from
>> +// ReplaceWithConstMap.
>> +bool GVN::replaceOperandsWithConsts(Instruction *Instr) const {
>> + bool Changed = false;
>> + for (unsigned OpNum = 0; OpNum < Instr->getNumOperands(); ++OpNum) {
>> + Value *Operand = Instr->getOperand(OpNum);
>> + auto it = ReplaceWithConstMap.find(Operand);
>> + if (it != ReplaceWithConstMap.end()) {
>> + Instr->setOperand(OpNum, it->second);
>> + Changed = true;
>> + }
>> + }
>> + return Changed;
>> +}
>> +
>> /// The given values are known to be equal in every block
>> /// dominated by 'Root'. Exploit this, for example by replacing 'LHS'
>> with
>> /// 'RHS' everywhere in the scope. Returns whether a change was made.
>> @@ -2048,11 +2101,13 @@ bool GVN::propagateEquality(Value *LHS,
>> std::pair<Value*, Value*> Item = Worklist.pop_back_val();
>> LHS = Item.first; RHS = Item.second;
>> - if (LHS == RHS) continue;
>> + if (LHS == RHS)
>> + continue;
>> assert(LHS->getType() == RHS->getType() && "Equality but unequal
>> types!");
>> // Don't try to propagate equalities between constants.
>> - if (isa<Constant>(LHS) && isa<Constant>(RHS)) continue;
>> + if (isa<Constant>(LHS) && isa<Constant>(RHS))
>> + continue;
>> // Prefer a constant on the right-hand side, or an Argument if no
>> constants.
>> if (isa<Constant>(LHS) || (isa<Argument>(LHS) &&
>> !isa<Constant>(RHS)))
>> @@ -2203,6 +2258,10 @@ bool GVN::processInstruction(Instruction
>> return true;
>> }
>> + if (IntrinsicInst *IntrinsicI = dyn_cast<IntrinsicInst>(I))
>> + if (IntrinsicI->getIntrinsicID() == Intrinsic::assume)
>> + return processAssumeIntrinsic(IntrinsicI);
>> +
>> if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
>> if (processLoad(LI))
>> return true;
>> @@ -2267,7 +2326,8 @@ bool GVN::processInstruction(Instruction
>> // Instructions with void type don't return a value, so there's
>> // no point in trying to find redundancies in them.
>> - if (I->getType()->isVoidTy()) return false;
>> + if (I->getType()->isVoidTy())
>> + return false;
>> uint32_t NextNum = VN.getNextUnusedValueNumber();
>> unsigned Num = VN.lookup_or_add(I);
>> @@ -2374,10 +2434,15 @@ bool GVN::processBlock(BasicBlock *BB) {
>> if (DeadBlocks.count(BB))
>> return false;
>> + // Clearing map before every BB because it can be used only for
>> single BB.
>> + ReplaceWithConstMap.clear();
>> bool ChangedFunction = false;
>> for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
>> BI != BE;) {
>> + if (!ReplaceWithConstMap.empty())
>> + ChangedFunction |= replaceOperandsWithConsts(BI);
>> +
>> ChangedFunction |= processInstruction(BI);
>> if (InstrsToErase.empty()) {
>> ++BI;
>>
>> Added: llvm/trunk/test/Transforms/GVN/assume-equal.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GVN/assume-equal.ll?rev=246243&view=auto
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/GVN/assume-equal.ll (added)
>> +++ llvm/trunk/test/Transforms/GVN/assume-equal.ll Thu Aug 27 20:01:57
>> 2015
>> @@ -0,0 +1,122 @@
>> +; RUN: opt < %s -gvn -S | FileCheck %s
>> +
>> +%struct.A = type { i32 (...)** }
>> + at _ZTV1A = available_externally unnamed_addr constant [4 x i8*] [i8*
>> null, i8* bitcast (i8** @_ZTI1A to i8*), i8* bitcast (i32 (%struct.A*)*
>> @_ZN1A3fooEv to i8*), i8* bitcast (i32 (%struct.A*)* @_ZN1A3barEv to i8*)],
>> align 8
>> + at _ZTI1A = external constant i8*
>> +
>> +; Checks if indirect calls can be replaced with direct
>> +; assuming that %vtable == @_ZTV1A (with alignment).
>> +; Checking const propagation across other BBs
>> +; CHECK-LABEL: define void @_Z1gb(
>> +
>> +define void @_Z1gb(i1 zeroext %p) {
>> +entry:
>> + %call = tail call noalias i8* @_Znwm(i64 8) #4
>> + %0 = bitcast i8* %call to %struct.A*
>> + tail call void @_ZN1AC1Ev(%struct.A* %0) #1
>> + %1 = bitcast i8* %call to i8***
>> + %vtable = load i8**, i8*** %1, align 8
>> + %cmp.vtables = icmp eq i8** %vtable, getelementptr inbounds ([4 x
>> i8*], [4 x i8*]* @_ZTV1A, i64 0, i64 2)
>> + tail call void @llvm.assume(i1 %cmp.vtables)
>> + br i1 %p, label %if.then, label %if.else
>> +
>> +if.then: ; preds = %entry
>> + %vtable1.cast = bitcast i8** %vtable to i32 (%struct.A*)**
>> + %2 = load i32 (%struct.A*)*, i32 (%struct.A*)** %vtable1.cast, align 8
>> +
>> + ; CHECK: call i32 @_ZN1A3fooEv(
>> + %call2 = tail call i32 %2(%struct.A* %0) #1
>> +
>> + br label %if.end
>> +
>> +if.else: ; preds = %entry
>> + %vfn47 = getelementptr inbounds i8*, i8** %vtable, i64 1
>> + %vfn4 = bitcast i8** %vfn47 to i32 (%struct.A*)**
>> +
>> + ; CHECK: call i32 @_ZN1A3barEv(
>> + %3 = load i32 (%struct.A*)*, i32 (%struct.A*)** %vfn4, align 8
>> +
>> + %call5 = tail call i32 %3(%struct.A* %0) #1
>> + br label %if.end
>> +
>> +if.end: ; preds = %if.else,
>> %if.then
>> + ret void
>> +}
>> +
>> +; Checking const propagation in the same BB
>> +; CHECK-LABEL: define i32 @main()
>> +
>> +define i32 @main() {
>> +entry:
>> + %call = tail call noalias i8* @_Znwm(i64 8)
>> + %0 = bitcast i8* %call to %struct.A*
>> + tail call void @_ZN1AC1Ev(%struct.A* %0)
>> + %1 = bitcast i8* %call to i8***
>> + %vtable = load i8**, i8*** %1, align 8
>> + %cmp.vtables = icmp eq i8** %vtable, getelementptr inbounds ([4 x
>> i8*], [4 x i8*]* @_ZTV1A, i64 0, i64 2)
>> + tail call void @llvm.assume(i1 %cmp.vtables)
>> + %vtable1.cast = bitcast i8** %vtable to i32 (%struct.A*)**
>> +
>> + ; CHECK: call i32 @_ZN1A3fooEv(
>> + %2 = load i32 (%struct.A*)*, i32 (%struct.A*)** %vtable1.cast, align 8
>> +
>> + %call2 = tail call i32 %2(%struct.A* %0)
>> + ret i32 0
>> +}
>> +
>> +; This tests checks const propatation with fcmp instruction.
>> +; CHECK-LABEL: define float @_Z1gf(float %p)
>> +
>> +define float @_Z1gf(float %p) {
>> +entry:
>> + %p.addr = alloca float, align 4
>> + %f = alloca float, align 4
>> + store float %p, float* %p.addr, align 4
>> +
>> + store float 3.000000e+00, float* %f, align 4
>> + %0 = load float, float* %p.addr, align 4
>> + %1 = load float, float* %f, align 4
>> + %cmp = fcmp oeq float %1, %0 ; note const on lhs
>> + call void @llvm.assume(i1 %cmp)
>> +
>> + ; CHECK: ret float 3.000000e+00
>> + ret float %0
>> +}
>> +
>> +; CHECK-LABEL: define float @_Z1hf(float %p)
>> +
>> +define float @_Z1hf(float %p) {
>> +entry:
>> + %p.addr = alloca float, align 4
>> + store float %p, float* %p.addr, align 4
>> +
>> + %0 = load float, float* %p.addr, align 4
>> + %cmp = fcmp nnan ueq float %0, 3.000000e+00
>> + call void @llvm.assume(i1 %cmp)
>> +
>> + ; CHECK: ret float 3.000000e+00
>> + ret float %0
>> +}
>> +
>> +; CHECK-LABEL: define float @_Z1if(float %p)
>> +
>> +
>> +define float @_Z1if(float %p) {
>> +entry:
>> + %p.addr = alloca float, align 4
>> + store float %p, float* %p.addr, align 4
>> +
>> + %0 = load float, float* %p.addr, align 4
>> + %cmp = fcmp ueq float %0, 3.000000e+00 ; no nnan flag - can't propagate
>> + call void @llvm.assume(i1 %cmp)
>> +
>> + ; CHECK-NOT: ret float 3.000000e+00
>> + ret float %0
>> +}
>> +
>> +declare noalias i8* @_Znwm(i64)
>> +declare void @_ZN1AC1Ev(%struct.A*)
>> +declare void @llvm.assume(i1)
>> +declare i32 @_ZN1A3fooEv(%struct.A*)
>> +declare i32 @_ZN1A3barEv(%struct.A*)
>> +
>>
>>
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>
>
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