[llvm] [Transforms][Utils][PromoteMem2Reg] Propagate nnan flag on par with the nsz flag (PR #114271)
Paul Osmialowski via llvm-commits
llvm-commits at lists.llvm.org
Wed Oct 30 10:16:38 PDT 2024
https://github.com/pawosm-arm created https://github.com/llvm/llvm-project/pull/114271
Following the change introduced by the PR #83381, this patch extends it with the same treatment of the nnan fast-math flag. This is to address the performance drop caused by PR#83200 which prevented vital InstCombine transformation due to the lack of relevant fast-math flags.
The PromoteMem2Reg utility is used by the SROA pass, where Phi nodes are being created. Proposed change allows propagation of the nnan flag down to these Phi nodes.
>From 234b4c33279a3c24824e45535e6b78de93a2234c Mon Sep 17 00:00:00 2001
From: Pawel Osmialowski <pawel.osmialowski at arm.com>
Date: Wed, 30 Oct 2024 14:30:08 +0000
Subject: [PATCH] [Transforms][Utils][PromoteMem2Reg] Propagate nnan flag on
par with the nsz flag
Following the change introduced by the PR #83381, this patch extends
it with the same treatment of the nnan fast-math flag. This is to
address the performance drop caused by PR#83200 which prevented vital
InstCombine transformation due to the lack of relevant fast-math
flags.
The PromoteMem2Reg utility is used by the SROA pass, where Phi nodes
are being created. Proposed change allows propagation of the nnan
flag down to these Phi nodes.
---
.../Utils/PromoteMemoryToRegister.cpp | 9 +++
.../SROA/propagate-fast-math-flags-on-phi.ll | 78 +++++++++++++++++++
2 files changed, 87 insertions(+)
diff --git a/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
index 656bb1ebd1161e..8a42bdddb08119 100644
--- a/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
+++ b/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -394,6 +394,9 @@ struct PromoteMem2Reg {
/// Whether the function has the no-signed-zeros-fp-math attribute set.
bool NoSignedZeros = false;
+ /// Whether the function has the no-nans-fp-math attribute set.
+ bool NoNaNs = false;
+
public:
PromoteMem2Reg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,
AssumptionCache *AC)
@@ -752,6 +755,7 @@ void PromoteMem2Reg::run() {
ForwardIDFCalculator IDF(DT);
NoSignedZeros = F.getFnAttribute("no-signed-zeros-fp-math").getValueAsBool();
+ NoNaNs = F.getFnAttribute("no-nans-fp-math").getValueAsBool();
for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
AllocaInst *AI = Allocas[AllocaNum];
@@ -1140,6 +1144,11 @@ void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
if (isa<FPMathOperator>(APN) && NoSignedZeros)
APN->setHasNoSignedZeros(true);
+ // This allows select instruction folding relevant to floating point
+ // reductions whose operand is a PHI.
+ if (isa<FPMathOperator>(APN) && NoNaNs)
+ APN->setHasNoNaNs(true);
+
// The currently active variable for this block is now the PHI.
IncomingVals[AllocaNo] = APN;
AllocaATInfo[AllocaNo].updateForNewPhi(APN, DIB);
diff --git a/llvm/test/Transforms/SROA/propagate-fast-math-flags-on-phi.ll b/llvm/test/Transforms/SROA/propagate-fast-math-flags-on-phi.ll
index 2cc26363daf9c5..4eda5108b7aba4 100644
--- a/llvm/test/Transforms/SROA/propagate-fast-math-flags-on-phi.ll
+++ b/llvm/test/Transforms/SROA/propagate-fast-math-flags-on-phi.ll
@@ -77,3 +77,81 @@ return: ; preds = %entry,%if.then
%retval = load double, ptr %x.addr
ret double %retval
}
+
+define double @phi_with_nnan(double %x) "no-nans-fp-math"="true" {
+; CHECK-LABEL: define double @phi_with_nnan(
+; CHECK-SAME: double [[X:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[CMP:%.*]] = fcmp olt double [[X]], 0.000000e+00
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[RETURN:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[FNEG:%.*]] = fneg double [[X]]
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: return:
+; CHECK-NEXT: [[X_ADDR_0:%.*]] = phi nnan double [ [[FNEG]], [[IF_THEN]] ], [ undef, [[ENTRY:%.*]] ]
+; CHECK-NEXT: ret double [[X_ADDR_0]]
+entry:
+ %x.addr = alloca double
+ %cmp = fcmp olt double %x, 0.0
+ br i1 %cmp, label %if.then, label %return
+
+if.then: ; preds = %entry
+ %fneg = fneg double %x
+ store double %fneg, ptr %x.addr
+ br label %return
+
+return: ; preds = %entry,%if.then
+ %retval = load double, ptr %x.addr
+ ret double %retval
+}
+
+define <2 x double> @vector_phi_with_nnan(<2 x double> %x, i1 %cmp, <2 x double> %a, <2 x double> %b) "no-nans-fp-math"="true" {
+; CHECK-LABEL: define <2 x double> @vector_phi_with_nnan(
+; CHECK-SAME: <2 x double> [[X:%.*]], i1 [[CMP:%.*]], <2 x double> [[A:%.*]], <2 x double> [[B:%.*]]) #[[ATTR0]] {
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[RETURN:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: return:
+; CHECK-NEXT: [[X_ADDR_0:%.*]] = phi nnan <2 x double> [ [[B]], [[IF_THEN]] ], [ [[A]], [[ENTRY:%.*]] ]
+; CHECK-NEXT: ret <2 x double> [[X_ADDR_0]]
+entry:
+ %x.addr = alloca <2 x double>
+ store <2 x double> %a, ptr %x.addr
+ br i1 %cmp, label %if.then, label %return
+
+if.then: ; preds = %entry
+ store <2 x double> %b, ptr %x.addr
+ br label %return
+
+return: ; preds = %entry,%if.then
+ %retval = load <2 x double>, ptr %x.addr
+ ret <2 x double> %retval
+}
+
+define double @phi_without_nnan(double %x) "no-nans-fp-math"="false" {
+; CHECK-LABEL: define double @phi_without_nnan(
+; CHECK-SAME: double [[X:%.*]]) #[[ATTR1:[0-9]+]] {
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[CMP:%.*]] = fcmp olt double [[X]], 0.000000e+00
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[RETURN:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[FNEG:%.*]] = fneg double [[X]]
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: return:
+; CHECK-NEXT: [[X_ADDR_0:%.*]] = phi double [ [[FNEG]], [[IF_THEN]] ], [ undef, [[ENTRY:%.*]] ]
+; CHECK-NEXT: ret double [[X_ADDR_0]]
+entry:
+ %x.addr = alloca double
+ %cmp = fcmp olt double %x, 0.0
+ br i1 %cmp, label %if.then, label %return
+
+if.then: ; preds = %entry
+ %fneg = fneg double %x
+ store double %fneg, ptr %x.addr
+ br label %return
+
+return: ; preds = %entry,%if.then
+ %retval = load double, ptr %x.addr
+ ret double %retval
+}
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