[llvm] 55be370 - [InstCombine] Fold frexp of select to select of frexp (#121227)
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llvm-commits at lists.llvm.org
Fri Jan 31 07:18:02 PST 2025
Author: Narayan
Date: 2025-01-31T23:17:58+08:00
New Revision: 55be370f375416f615a840d1c0cabe2c819e6bbb
URL: https://github.com/llvm/llvm-project/commit/55be370f375416f615a840d1c0cabe2c819e6bbb
DIFF: https://github.com/llvm/llvm-project/commit/55be370f375416f615a840d1c0cabe2c819e6bbb.diff
LOG: [InstCombine] Fold frexp of select to select of frexp (#121227)
This patch implements an optimization to push select operations through
frexp when one of the select operands is a constant. When we encounter:
```
define float @src(float %x, i1 %bool) {
%select = select i1 %bool, float 1.000000e+00, float %x
%frexp = tail call { float, i32 } @llvm.frexp.f32.i32(float %select)
%frexp.0 = extractvalue { float, i32 } %frexp, 0
ret float %frexp.0
}
```
We transform it to:
```
define float @tgt(float %x, i1 %bool) {
%frexp = tail call { float, i32 } @llvm.frexp.f32.i32(float %x)
%frexp.0 = extractvalue { float, i32 } %frexp, 0
%select = select i1 %bool, float 5.000000e-01, float %frexp.0
ret float %select
}
```
Fixes #92542
Added:
llvm/test/Transforms/InstCombine/select_frexp.ll
Modified:
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index a64c188575e6c3..5621511570b581 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -33,6 +33,7 @@
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
+#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
@@ -4069,6 +4070,49 @@ InstCombinerImpl::foldExtractOfOverflowIntrinsic(ExtractValueInst &EV) {
return nullptr;
}
+static Value *foldFrexpOfSelect(ExtractValueInst &EV, IntrinsicInst *FrexpCall,
+ SelectInst *SelectInst,
+ InstCombiner::BuilderTy &Builder) {
+ // Helper to fold frexp of select to select of frexp.
+
+ if (!SelectInst->hasOneUse() || !FrexpCall->hasOneUse())
+ return nullptr;
+ Value *Cond = SelectInst->getCondition();
+ Value *TrueVal = SelectInst->getTrueValue();
+ Value *FalseVal = SelectInst->getFalseValue();
+
+ const APFloat *ConstVal = nullptr;
+ Value *VarOp = nullptr;
+ bool ConstIsTrue = false;
+
+ if (match(TrueVal, m_APFloat(ConstVal))) {
+ VarOp = FalseVal;
+ ConstIsTrue = true;
+ } else if (match(FalseVal, m_APFloat(ConstVal))) {
+ VarOp = TrueVal;
+ ConstIsTrue = false;
+ } else {
+ return nullptr;
+ }
+
+ Builder.SetInsertPoint(&EV);
+
+ CallInst *NewFrexp =
+ Builder.CreateCall(FrexpCall->getCalledFunction(), {VarOp}, "frexp");
+ NewFrexp->copyIRFlags(FrexpCall);
+
+ Value *NewEV = Builder.CreateExtractValue(NewFrexp, 0, "mantissa");
+
+ int Exp;
+ APFloat Mantissa = frexp(*ConstVal, Exp, APFloat::rmNearestTiesToEven);
+
+ Constant *ConstantMantissa = ConstantFP::get(TrueVal->getType(), Mantissa);
+
+ Value *NewSel = Builder.CreateSelectFMF(
+ Cond, ConstIsTrue ? ConstantMantissa : NewEV,
+ ConstIsTrue ? NewEV : ConstantMantissa, SelectInst, "select.frexp");
+ return NewSel;
+}
Instruction *InstCombinerImpl::visitExtractValueInst(ExtractValueInst &EV) {
Value *Agg = EV.getAggregateOperand();
@@ -4079,6 +4123,15 @@ Instruction *InstCombinerImpl::visitExtractValueInst(ExtractValueInst &EV) {
SQ.getWithInstruction(&EV)))
return replaceInstUsesWith(EV, V);
+ Value *Cond, *TrueVal, *FalseVal;
+ if (match(&EV, m_ExtractValue<0>(m_Intrinsic<Intrinsic::frexp>(m_Select(
+ m_Value(Cond), m_Value(TrueVal), m_Value(FalseVal)))))) {
+ auto *SelInst =
+ cast<SelectInst>(cast<IntrinsicInst>(Agg)->getArgOperand(0));
+ if (Value *Result =
+ foldFrexpOfSelect(EV, cast<IntrinsicInst>(Agg), SelInst, Builder))
+ return replaceInstUsesWith(EV, Result);
+ }
if (InsertValueInst *IV = dyn_cast<InsertValueInst>(Agg)) {
// We're extracting from an insertvalue instruction, compare the indices
const unsigned *exti, *exte, *insi, *inse;
diff --git a/llvm/test/Transforms/InstCombine/select_frexp.ll b/llvm/test/Transforms/InstCombine/select_frexp.ll
new file mode 100644
index 00000000000000..d025aedda7170d
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/select_frexp.ll
@@ -0,0 +1,191 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=instcombine -S < %s | FileCheck %s
+
+declare { float, i32 } @llvm.frexp.f32.i32(float)
+declare void @use(float)
+
+; Basic test case - constant in true position
+define float @test_select_frexp_basic(float %x, i1 %cond) {
+; CHECK-LABEL: define float @test_select_frexp_basic(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT: [[FREXP:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[X]])
+; CHECK-NEXT: [[FREXP_0:%.*]] = extractvalue { float, i32 } [[FREXP]], 0
+; CHECK-NEXT: [[SELECT_FREXP:%.*]] = select i1 [[COND]], float 5.000000e-01, float [[FREXP_0]]
+; CHECK-NEXT: ret float [[SELECT_FREXP]]
+;
+ %sel = select i1 %cond, float 1.000000e+00, float %x
+ %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+ %frexp.0 = extractvalue { float, i32 } %frexp, 0
+ ret float %frexp.0
+}
+
+; Test with constant in false position
+define float @test_select_frexp_const_false(float %x, i1 %cond) {
+; CHECK-LABEL: define float @test_select_frexp_const_false(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT: [[FREXP:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[X]])
+; CHECK-NEXT: [[FREXP_0:%.*]] = extractvalue { float, i32 } [[FREXP]], 0
+; CHECK-NEXT: [[SELECT_FREXP:%.*]] = select i1 [[COND]], float [[FREXP_0]], float 5.000000e-01
+; CHECK-NEXT: ret float [[SELECT_FREXP]]
+;
+ %sel = select i1 %cond, float %x, float 1.000000e+00
+ %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+ %frexp.0 = extractvalue { float, i32 } %frexp, 0
+ ret float %frexp.0
+}
+
+; Multi-use test
+define float @test_select_frexp_multi_use(float %x, i1 %cond) {
+; CHECK-LABEL: define float @test_select_frexp_multi_use(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], float 1.000000e+00, float [[X]]
+; CHECK-NEXT: call void @use(float [[SEL]])
+; CHECK-NEXT: [[FREXP:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[SEL]])
+; CHECK-NEXT: [[FREXP_0:%.*]] = extractvalue { float, i32 } [[FREXP]], 0
+; CHECK-NEXT: ret float [[FREXP_0]]
+;
+ %sel = select i1 %cond, float 1.000000e+00, float %x
+ call void @use(float %sel)
+ %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+ %frexp.0 = extractvalue { float, i32 } %frexp, 0
+ ret float %frexp.0
+}
+
+; Vector test - splat constant
+define <2 x float> @test_select_frexp_vec_splat(<2 x float> %x, <2 x i1> %cond) {
+; CHECK-LABEL: define <2 x float> @test_select_frexp_vec_splat(
+; CHECK-SAME: <2 x float> [[X:%.*]], <2 x i1> [[COND:%.*]]) {
+; CHECK-NEXT: [[FREXP:%.*]] = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> [[X]])
+; CHECK-NEXT: [[FREXP_0:%.*]] = extractvalue { <2 x float>, <2 x i32> } [[FREXP]], 0
+; CHECK-NEXT: [[SELECT_FREXP:%.*]] = select <2 x i1> [[COND]], <2 x float> splat (float 5.000000e-01), <2 x float> [[FREXP_0]]
+; CHECK-NEXT: ret <2 x float> [[SELECT_FREXP]]
+;
+ %sel = select <2 x i1> %cond, <2 x float> <float 1.000000e+00, float 1.000000e+00>, <2 x float> %x
+ %frexp = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> %sel)
+ %frexp.0 = extractvalue { <2 x float>, <2 x i32> } %frexp, 0
+ ret <2 x float> %frexp.0
+}
+
+; Vector test with poison
+define <2 x float> @test_select_frexp_vec_poison(<2 x float> %x, <2 x i1> %cond) {
+; CHECK-LABEL: define <2 x float> @test_select_frexp_vec_poison(
+; CHECK-SAME: <2 x float> [[X:%.*]], <2 x i1> [[COND:%.*]]) {
+; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[COND]], <2 x float> <float 1.000000e+00, float poison>, <2 x float> [[X]]
+; CHECK-NEXT: [[FREXP:%.*]] = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> [[SEL]])
+; CHECK-NEXT: [[FREXP_0:%.*]] = extractvalue { <2 x float>, <2 x i32> } [[FREXP]], 0
+; CHECK-NEXT: ret <2 x float> [[FREXP_0]]
+;
+ %sel = select <2 x i1> %cond, <2 x float> <float 1.000000e+00, float poison>, <2 x float> %x
+ %frexp = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> %sel)
+ %frexp.0 = extractvalue { <2 x float>, <2 x i32> } %frexp, 0
+ ret <2 x float> %frexp.0
+}
+
+; Vector test - non-splat (should not fold)
+define <2 x float> @test_select_frexp_vec_nonsplat(<2 x float> %x, <2 x i1> %cond) {
+; CHECK-LABEL: define <2 x float> @test_select_frexp_vec_nonsplat(
+; CHECK-SAME: <2 x float> [[X:%.*]], <2 x i1> [[COND:%.*]]) {
+; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[COND]], <2 x float> <float 1.000000e+00, float 2.000000e+00>, <2 x float> [[X]]
+; CHECK-NEXT: [[FREXP:%.*]] = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> [[SEL]])
+; CHECK-NEXT: [[FREXP_0:%.*]] = extractvalue { <2 x float>, <2 x i32> } [[FREXP]], 0
+; CHECK-NEXT: ret <2 x float> [[FREXP_0]]
+;
+ %sel = select <2 x i1> %cond, <2 x float> <float 1.000000e+00, float 2.000000e+00>, <2 x float> %x
+ %frexp = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> %sel)
+ %frexp.0 = extractvalue { <2 x float>, <2 x i32> } %frexp, 0
+ ret <2 x float> %frexp.0
+}
+
+; Negative test - both operands non-constant
+define float @test_select_frexp_no_const(float %x, float %y, i1 %cond) {
+; CHECK-LABEL: define float @test_select_frexp_no_const(
+; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], float [[X]], float [[Y]]
+; CHECK-NEXT: [[FREXP:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[SEL]])
+; CHECK-NEXT: [[FREXP_0:%.*]] = extractvalue { float, i32 } [[FREXP]], 0
+; CHECK-NEXT: ret float [[FREXP_0]]
+;
+ %sel = select i1 %cond, float %x, float %y
+ %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+ %frexp.0 = extractvalue { float, i32 } %frexp, 0
+ ret float %frexp.0
+}
+
+; Negative test - extracting exp instead of mantissa
+define i32 @test_select_frexp_extract_exp(float %x, i1 %cond) {
+; CHECK-LABEL: define i32 @test_select_frexp_extract_exp(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND]], float 1.000000e+00, float [[X]]
+; CHECK-NEXT: [[FREXP:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[SEL]])
+; CHECK-NEXT: [[FREXP_1:%.*]] = extractvalue { float, i32 } [[FREXP]], 1
+; CHECK-NEXT: ret i32 [[FREXP_1]]
+;
+ %sel = select i1 %cond, float 1.000000e+00, float %x
+ %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+ %frexp.1 = extractvalue { float, i32 } %frexp, 1
+ ret i32 %frexp.1
+}
+
+; Test with fast math flags
+define float @test_select_frexp_fast_math_select(float %x, i1 %cond) {
+; CHECK-LABEL: define float @test_select_frexp_fast_math_select(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT: [[FREXP1:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[X]])
+; CHECK-NEXT: [[MANTISSA:%.*]] = extractvalue { float, i32 } [[FREXP1]], 0
+; CHECK-NEXT: [[SELECT_FREXP:%.*]] = select nnan ninf nsz i1 [[COND]], float 5.000000e-01, float [[MANTISSA]]
+; CHECK-NEXT: ret float [[SELECT_FREXP]]
+;
+ %sel = select nnan ninf nsz i1 %cond, float 1.000000e+00, float %x
+ %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+ %frexp.0 = extractvalue { float, i32 } %frexp, 0
+ ret float %frexp.0
+}
+
+
+; Test vector case with fast math flags
+define <2 x float> @test_select_frexp_vec_fast_math(<2 x float> %x, <2 x i1> %cond) {
+; CHECK-LABEL: define <2 x float> @test_select_frexp_vec_fast_math(
+; CHECK-SAME: <2 x float> [[X:%.*]], <2 x i1> [[COND:%.*]]) {
+; CHECK-NEXT: [[FREXP1:%.*]] = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> [[X]])
+; CHECK-NEXT: [[MANTISSA:%.*]] = extractvalue { <2 x float>, <2 x i32> } [[FREXP1]], 0
+; CHECK-NEXT: [[SELECT_FREXP:%.*]] = select nnan ninf nsz <2 x i1> [[COND]], <2 x float> splat (float 5.000000e-01), <2 x float> [[MANTISSA]]
+; CHECK-NEXT: ret <2 x float> [[SELECT_FREXP]]
+;
+ %sel = select nnan ninf nsz <2 x i1> %cond, <2 x float> <float 1.000000e+00, float 1.000000e+00>, <2 x float> %x
+ %frexp = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> %sel)
+ %frexp.0 = extractvalue { <2 x float>, <2 x i32> } %frexp, 0
+ ret <2 x float> %frexp.0
+}
+
+; Test with scalable vectors with constant at True Position
+define <vscale x 2 x float> @test_select_frexp_scalable_vec0(<vscale x 2 x float> %x, <vscale x 2 x i1> %cond) {
+; CHECK-LABEL: define <vscale x 2 x float> @test_select_frexp_scalable_vec0(
+; CHECK-SAME: <vscale x 2 x float> [[X:%.*]], <vscale x 2 x i1> [[COND:%.*]]) {
+; CHECK-NEXT: [[FREXP1:%.*]] = call { <vscale x 2 x float>, <vscale x 2 x i32> } @llvm.frexp.nxv2f32.nxv2i32(<vscale x 2 x float> [[X]])
+; CHECK-NEXT: [[MANTISSA:%.*]] = extractvalue { <vscale x 2 x float>, <vscale x 2 x i32> } [[FREXP1]], 0
+; CHECK-NEXT: [[SELECT_FREXP:%.*]] = select <vscale x 2 x i1> [[COND]], <vscale x 2 x float> splat (float 5.000000e-01), <vscale x 2 x float> [[MANTISSA]]
+; CHECK-NEXT: ret <vscale x 2 x float> [[SELECT_FREXP]]
+;
+ %sel = select <vscale x 2 x i1> %cond, <vscale x 2 x float> splat (float 1.000000e+00), <vscale x 2 x float> %x
+ %frexp = call { <vscale x 2 x float>, <vscale x 2 x i32> } @llvm.frexp.nxv2f32.nxv2i32(<vscale x 2 x float> %sel)
+ %frexp.0 = extractvalue { <vscale x 2 x float>, <vscale x 2 x i32> } %frexp, 0
+ ret <vscale x 2 x float> %frexp.0
+}
+
+; Test with scalable vectors with constant at False Position
+define <vscale x 2 x float> @test_select_frexp_scalable_vec1(<vscale x 2 x float> %x, <vscale x 2 x i1> %cond) {
+; CHECK-LABEL: define <vscale x 2 x float> @test_select_frexp_scalable_vec1(
+; CHECK-SAME: <vscale x 2 x float> [[X:%.*]], <vscale x 2 x i1> [[COND:%.*]]) {
+; CHECK-NEXT: [[FREXP1:%.*]] = call { <vscale x 2 x float>, <vscale x 2 x i32> } @llvm.frexp.nxv2f32.nxv2i32(<vscale x 2 x float> [[X]])
+; CHECK-NEXT: [[MANTISSA:%.*]] = extractvalue { <vscale x 2 x float>, <vscale x 2 x i32> } [[FREXP1]], 0
+; CHECK-NEXT: [[SELECT_FREXP:%.*]] = select <vscale x 2 x i1> [[COND]], <vscale x 2 x float> [[MANTISSA]], <vscale x 2 x float> splat (float 5.000000e-01)
+; CHECK-NEXT: ret <vscale x 2 x float> [[SELECT_FREXP]]
+;
+ %sel = select <vscale x 2 x i1> %cond, <vscale x 2 x float> %x, <vscale x 2 x float> splat (float 1.000000e+00)
+ %frexp = call { <vscale x 2 x float>, <vscale x 2 x i32> } @llvm.frexp.nxv2f32.nxv2i32(<vscale x 2 x float> %sel)
+ %frexp.0 = extractvalue { <vscale x 2 x float>, <vscale x 2 x i32> } %frexp, 0
+ ret <vscale x 2 x float> %frexp.0
+}
+
+declare { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float>)
+declare { <vscale x 2 x float>, <vscale x 2 x i32> } @llvm.frexp.nxv2f32.nxv2i32(<vscale x 2 x float>)
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