[llvm] r245265 - Constant propagation after hiting llvm.assume
Piotr Padlewski via llvm-commits
llvm-commits at lists.llvm.org
Mon Aug 17 20:55:31 PDT 2015
Author: prazek
Date: Mon Aug 17 22:55:30 2015
New Revision: 245265
URL: http://llvm.org/viewvc/llvm-project?rev=245265&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=245265&r1=245264&r2=245265&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Mon Aug 17 22:55:30 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);
@@ -1759,6 +1765,38 @@ 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
@@ -2031,6 +2069,21 @@ 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.
@@ -2047,11 +2100,13 @@ 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)))
@@ -2202,6 +2257,10 @@ 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;
@@ -2266,7 +2325,8 @@ 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);
@@ -2373,10 +2433,15 @@ 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=245265&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/GVN/assume-equal.ll (added)
+++ llvm/trunk/test/Transforms/GVN/assume-equal.ll Mon Aug 17 22:55:30 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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