[llvm] [InstCombine] Add log-pow simplification for FP exponent edge case. (PR #76641)
via llvm-commits
llvm-commits at lists.llvm.org
Wed Jan 3 10:36:49 PST 2024
https://github.com/tanmaysachan updated https://github.com/llvm/llvm-project/pull/76641
>From 10bc58b9c784971786a2ba11f6547c64422e9a85 Mon Sep 17 00:00:00 2001
From: tanmaysachan <tnmysachan at gmail.com>
Date: Sun, 31 Dec 2023 11:19:16 +0530
Subject: [PATCH 1/5] Add log-powi simplification tests.
* Current tests do not cover ideal behaviour for the expression `log(powi(x, y)) --> y * log(x)` where y is an integer.
---
llvm/test/Transforms/InstCombine/log-pow.ll | 23 +++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/log-pow.ll b/llvm/test/Transforms/InstCombine/log-pow.ll
index 58f04da280beee..c4972f5a0253cb 100644
--- a/llvm/test/Transforms/InstCombine/log-pow.ll
+++ b/llvm/test/Transforms/InstCombine/log-pow.ll
@@ -12,6 +12,28 @@ define double @log_pow(double %x, double %y) {
ret double %log
}
+define double @log_powi_const(double %x) {
+; CHECK-LABEL: @log_powi_const(
+; CHECK-NEXT: [[LOG1:%.*]] = call fast double @llvm.log.f64(double [[X:%.*]])
+; CHECK-NEXT: [[MUL:%.*]] = fmul fast double [[LOG1]], -3.000000e+00
+; CHECK-NEXT: ret double [[MUL]]
+;
+ %pow = call fast double @llvm.powi.f64.i32(double %x, i32 -3)
+ %log = call fast double @log(double %pow)
+ ret double %log
+}
+
+define double @log_powi_nonconst(double %x, i32 %y) {
+; CHECK-LABEL: @log_powi_nonconst(
+; CHECK-NEXT: [[LOG1:%.*]] = call fast double @llvm.log.f64(double [[X:%.*]])
+; CHECK-NEXT: [[CAST:%.*]] = sitofp i32 [[Y:%.*]] to double
+; CHECK-NEXT: [[MUL:%.*]] = fmul fast double [[LOG1]], [[CAST]]
+; CHECK-NEXT: ret double [[MUL]]
+ %pow = call fast double @llvm.powi.f64.i32(double %x, i32 %y)
+ %log = call fast double @log(double %pow)
+ ret double %log
+}
+
define float @log10f_powf(float %x, float %y) {
; CHECK-LABEL: @log10f_powf(
; CHECK-NEXT: [[LOG1:%.*]] = call fast float @llvm.log10.f32(float [[X:%.*]])
@@ -128,6 +150,7 @@ declare float @exp10f(float) #0
declare <2 x float> @llvm.exp2.v2f32(<2 x float>)
declare double @pow(double, double) #0
declare float @powf(float, float) #0
+declare double @llvm.powi.f64.i32(double, i32) #0
declare <2 x double> @llvm.pow.v2f64(<2 x double>, <2 x double>)
attributes #0 = { nounwind readnone }
>From 50437a585b8f6965d2997ff8672fcc8c4463655a Mon Sep 17 00:00:00 2001
From: tanmaysachan <tnmysachan at gmail.com>
Date: Sun, 31 Dec 2023 11:21:42 +0530
Subject: [PATCH 2/5] Fix missed optimization for log-pow.
* Current simplification for `log(pow(x, y)) --> y * log(x)` does not work for `powi()`.
* This patch adds a cast for exponent to FP if it is integer, which enables this optimization.
---
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 760a626c8b6fcb..5aaa1d9d09ce3d 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -2495,13 +2495,21 @@ Value *LibCallSimplifier::optimizeLog(CallInst *Log, IRBuilderBase &B) {
// log(pow(x,y)) -> y*log(x)
AttributeList NoAttrs;
- if (ArgLb == PowLb || ArgID == Intrinsic::pow) {
+ if (ArgLb == PowLb || ArgID == Intrinsic::pow || ArgID == Intrinsic::powi) {
Value *LogX =
Log->doesNotAccessMemory()
? B.CreateCall(Intrinsic::getDeclaration(Mod, LogID, Ty),
Arg->getOperand(0), "log")
: emitUnaryFloatFnCall(Arg->getOperand(0), TLI, LogNm, B, NoAttrs);
- Value *MulY = B.CreateFMul(Arg->getArgOperand(1), LogX, "mul");
+ Value *Y = Arg->getArgOperand(1);
+ // Cast exponent to FP if integer.
+ if (ArgID == Intrinsic::powi) {
+ if (ConstantInt *C = dyn_cast<ConstantInt>(Y))
+ Y = ConstantFoldCastOperand(Instruction::SIToFP, C, Log->getType(), DL);
+ else
+ Y = B.CreateCast(Instruction::SIToFP, Y, Ty, "cast");
+ }
+ Value *MulY = B.CreateFMul(Y, LogX, "mul");
// Since pow() may have side effects, e.g. errno,
// dead code elimination may not be trusted to remove it.
substituteInParent(Arg, MulY);
>From 556cfbbec54d5b85d318109fff8c3cce5e9584ab Mon Sep 17 00:00:00 2001
From: tanmaysachan <tnmysachan at gmail.com>
Date: Wed, 3 Jan 2024 20:41:14 +0530
Subject: [PATCH 3/5] fixup! Fix missed optimization for log-pow.
---
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 5aaa1d9d09ce3d..d19a5dc9994b7b 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -2505,7 +2505,7 @@ Value *LibCallSimplifier::optimizeLog(CallInst *Log, IRBuilderBase &B) {
// Cast exponent to FP if integer.
if (ArgID == Intrinsic::powi) {
if (ConstantInt *C = dyn_cast<ConstantInt>(Y))
- Y = ConstantFoldCastOperand(Instruction::SIToFP, C, Log->getType(), DL);
+ Y = ConstantFoldCastOperand(Instruction::SIToFP, C, Ty, DL);
else
Y = B.CreateCast(Instruction::SIToFP, Y, Ty, "cast");
}
>From 39c428a696af89d4a01eccb2ee057e48098d9bbe Mon Sep 17 00:00:00 2001
From: tanmaysachan <tnmysachan at gmail.com>
Date: Wed, 3 Jan 2024 23:18:52 +0530
Subject: [PATCH 4/5] fixup! fixup! Fix missed optimization for log-pow.
---
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index d19a5dc9994b7b..3b65d8da52250c 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -2503,12 +2503,8 @@ Value *LibCallSimplifier::optimizeLog(CallInst *Log, IRBuilderBase &B) {
: emitUnaryFloatFnCall(Arg->getOperand(0), TLI, LogNm, B, NoAttrs);
Value *Y = Arg->getArgOperand(1);
// Cast exponent to FP if integer.
- if (ArgID == Intrinsic::powi) {
- if (ConstantInt *C = dyn_cast<ConstantInt>(Y))
- Y = ConstantFoldCastOperand(Instruction::SIToFP, C, Ty, DL);
- else
+ if (ArgID == Intrinsic::powi)
Y = B.CreateCast(Instruction::SIToFP, Y, Ty, "cast");
- }
Value *MulY = B.CreateFMul(Y, LogX, "mul");
// Since pow() may have side effects, e.g. errno,
// dead code elimination may not be trusted to remove it.
>From 229602efe4d840764972e851044d3d95cc9ef780 Mon Sep 17 00:00:00 2001
From: tanmaysachan <tnmysachan at gmail.com>
Date: Thu, 4 Jan 2024 00:06:35 +0530
Subject: [PATCH 5/5] fixup! fixup! fixup! Fix missed optimization for log-pow.
---
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 3b65d8da52250c..35693ebb4cc189 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -2504,7 +2504,7 @@ Value *LibCallSimplifier::optimizeLog(CallInst *Log, IRBuilderBase &B) {
Value *Y = Arg->getArgOperand(1);
// Cast exponent to FP if integer.
if (ArgID == Intrinsic::powi)
- Y = B.CreateCast(Instruction::SIToFP, Y, Ty, "cast");
+ Y = B.CreateCast(Instruction::SIToFP, Y, Ty, "cast");
Value *MulY = B.CreateFMul(Y, LogX, "mul");
// Since pow() may have side effects, e.g. errno,
// dead code elimination may not be trusted to remove it.
More information about the llvm-commits
mailing list