[llvm] 9fac110 - Revert "[InstCombine] fold fcmp with lossy casted constant"
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Thu Mar 10 07:25:14 PST 2022
Author: Sanjay Patel
Date: 2022-03-10T10:22:22-05:00
New Revision: 9fac110bf70896a5411cf57b3ff34fab5798ab78
URL: https://github.com/llvm/llvm-project/commit/9fac110bf70896a5411cf57b3ff34fab5798ab78
DIFF: https://github.com/llvm/llvm-project/commit/9fac110bf70896a5411cf57b3ff34fab5798ab78.diff
LOG: Revert "[InstCombine] fold fcmp with lossy casted constant"
This reverts commit 9397bdc67eb2b9eedc247a89bef01c2484b48b89.
This optimization is likely to surprise programmers as seen
in post-commit comments, so we should add a clang warning
first (that is proposed in D121306).
Added:
Modified:
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
llvm/test/Transforms/InstCombine/fcmp.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index e405dc7334b49..d3f6693b16db2 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -6654,6 +6654,7 @@ Instruction *InstCombinerImpl::visitFCmpInst(FCmpInst &I) {
if (match(Op1, m_FPExt(m_Value(Y))) && X->getType() == Y->getType())
return new FCmpInst(Pred, X, Y, "", &I);
+ // fcmp (fpext X), C -> fcmp X, (fptrunc C) if fptrunc is lossless
const APFloat *C;
if (match(Op1, m_APFloat(C))) {
const fltSemantics &FPSem =
@@ -6662,31 +6663,6 @@ Instruction *InstCombinerImpl::visitFCmpInst(FCmpInst &I) {
APFloat TruncC = *C;
TruncC.convert(FPSem, APFloat::rmNearestTiesToEven, &Lossy);
- if (Lossy) {
- // X can't possibly equal the higher-precision constant, so reduce any
- // equality comparison.
- // TODO: Other predicates can be handled via getFCmpCode().
- switch (Pred) {
- case FCmpInst::FCMP_OEQ:
- // X is ordered and equal to an impossible constant --> false
- return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
- case FCmpInst::FCMP_ONE:
- // X is ordered and not equal to an impossible constant --> ordered
- return new FCmpInst(FCmpInst::FCMP_ORD, X,
- ConstantFP::getNullValue(X->getType()));
- case FCmpInst::FCMP_UEQ:
- // X is unordered or equal to an impossible constant --> unordered
- return new FCmpInst(FCmpInst::FCMP_UNO, X,
- ConstantFP::getNullValue(X->getType()));
- case FCmpInst::FCMP_UNE:
- // X is unordered or not equal to an impossible constant --> true
- return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
- default:
- break;
- }
- }
-
- // fcmp (fpext X), C -> fcmp X, (fptrunc C) if fptrunc is lossless
// Avoid lossy conversions and denormals.
// Zero is a special case that's OK to convert.
APFloat Fabs = TruncC;
diff --git a/llvm/test/Transforms/InstCombine/fcmp.ll b/llvm/test/Transforms/InstCombine/fcmp.ll
index fb6309262de59..de8328c35ec02 100644
--- a/llvm/test/Transforms/InstCombine/fcmp.ll
+++ b/llvm/test/Transforms/InstCombine/fcmp.ll
@@ -674,7 +674,9 @@ define i1 @is_signbit_set_simplify_nan(double %x) {
define <2 x i1> @lossy_oeq(<2 x float> %x) {
; CHECK-LABEL: @lossy_oeq(
-; CHECK-NEXT: ret <2 x i1> zeroinitializer
+; CHECK-NEXT: [[E:%.*]] = fpext <2 x float> [[X:%.*]] to <2 x double>
+; CHECK-NEXT: [[R:%.*]] = fcmp oeq <2 x double> [[E]], <double 1.000000e-01, double 1.000000e-01>
+; CHECK-NEXT: ret <2 x i1> [[R]]
;
%e = fpext <2 x float> %x to <2 x double>
%r = fcmp oeq <2 x double> %e, <double 0.1, double 0.1>
@@ -685,7 +687,7 @@ define i1 @lossy_one(float %x, double* %p) {
; CHECK-LABEL: @lossy_one(
; CHECK-NEXT: [[E:%.*]] = fpext float [[X:%.*]] to double
; CHECK-NEXT: store double [[E]], double* [[P:%.*]], align 8
-; CHECK-NEXT: [[R:%.*]] = fcmp ord float [[X]], 0.000000e+00
+; CHECK-NEXT: [[R:%.*]] = fcmp one double [[E]], 1.000000e-01
; CHECK-NEXT: ret i1 [[R]]
;
%e = fpext float %x to double
@@ -696,7 +698,8 @@ define i1 @lossy_one(float %x, double* %p) {
define i1 @lossy_ueq(half %x) {
; CHECK-LABEL: @lossy_ueq(
-; CHECK-NEXT: [[R:%.*]] = fcmp uno half [[X:%.*]], 0xH0000
+; CHECK-NEXT: [[E:%.*]] = fpext half [[X:%.*]] to double
+; CHECK-NEXT: [[R:%.*]] = fcmp ueq double [[E]], 6.553600e+04
; CHECK-NEXT: ret i1 [[R]]
;
%e = fpext half %x to double
@@ -706,7 +709,9 @@ define i1 @lossy_ueq(half %x) {
define i1 @lossy_une(half %x) {
; CHECK-LABEL: @lossy_une(
-; CHECK-NEXT: ret i1 true
+; CHECK-NEXT: [[E:%.*]] = fpext half [[X:%.*]] to float
+; CHECK-NEXT: [[R:%.*]] = fcmp une float [[E]], 2.049000e+03
+; CHECK-NEXT: ret i1 [[R]]
;
%e = fpext half %x to float
%r = fcmp une float %e, 2049.0
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