[llvm-branch-commits] [llvm] InstCombine: Fold known-qnan results to a literal nan (PR #176123)
Matt Arsenault via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Thu Jan 15 12:00:32 PST 2026
https://github.com/arsenm updated https://github.com/llvm/llvm-project/pull/176123
>From 03d27f4a441697c60e9da391e24b7684e4589933 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Thu, 15 Jan 2026 11:21:53 +0100
Subject: [PATCH 1/3] InstCombine: Fold known-qnan results to a literal nan
Previously we only considered fcNan to fold to qnan for canonicalizing
results, ignoring the simpler case where we know the nan is already
quiet.
---
.../InstCombine/InstCombineSimplifyDemanded.cpp | 2 ++
.../InstCombine/simplify-demanded-fpclass-exp.ll | 2 +-
.../simplify-demanded-fpclass-extractelement.ll | 3 +--
.../InstCombine/simplify-demanded-fpclass-fadd.ll | 3 +--
.../InstCombine/simplify-demanded-fpclass-fmul.ll | 6 ++----
.../InstCombine/simplify-demanded-fpclass-fpext.ll | 3 +--
.../simplify-demanded-fpclass-fptrunc-round.ll | 3 +--
.../InstCombine/simplify-demanded-fpclass-fptrunc.ll | 3 +--
.../InstCombine/simplify-demanded-fpclass-frexp.ll | 7 +++----
.../simplify-demanded-fpclass-insertelement.ll | 7 +++----
.../InstCombine/simplify-demanded-fpclass-maximum.ll | 3 +--
.../simplify-demanded-fpclass-maximumnum.ll | 3 +--
.../InstCombine/simplify-demanded-fpclass-minimum.ll | 3 +--
.../simplify-demanded-fpclass-minimumnum.ll | 3 +--
.../simplify-demanded-fpclass-rounding-intrinsics.ll | 3 +--
.../simplify-demanded-fpclass-shufflevector.ll | 7 +++----
.../InstCombine/simplify-demanded-fpclass-sqrt.ll | 12 +++---------
.../InstCombine/simplify-demanded-fpclass.ll | 2 +-
18 files changed, 28 insertions(+), 47 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index db8193f97ccf8..de1da8acae47a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -2028,6 +2028,8 @@ static Constant *getFPClassConstant(Type *Ty, FPClassTest Mask,
return ConstantFP::getInfinity(Ty);
case fcNegInf:
return ConstantFP::getInfinity(Ty, true);
+ case fcQNan:
+ return ConstantFP::getQNaN(Ty);
default:
return nullptr;
}
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-exp.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-exp.ll
index ef68699c73166..2a33ff195911e 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-exp.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-exp.ll
@@ -490,7 +490,7 @@ define nofpclass(nzero) float @source_is_known_snan(float nofpclass(inf norm sub
define nofpclass(nzero) float @source_is_known_qnan(float nofpclass(inf norm sub zero snan) %must.be.qnan) {
; CHECK-LABEL: define nofpclass(nzero) float @source_is_known_qnan(
; CHECK-SAME: float nofpclass(snan inf zero sub norm) [[MUST_BE_QNAN:%.*]]) {
-; CHECK-NEXT: ret float [[MUST_BE_QNAN]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%exp = call float @llvm.exp2.f32(float %must.be.qnan)
ret float %exp
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-extractelement.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-extractelement.ll
index e571774c72f2b..6cabee258d2b6 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-extractelement.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-extractelement.ll
@@ -17,8 +17,7 @@ define nofpclass(inf norm sub zero) half @ret_only_nan__extractelement_unknown(<
define nofpclass(snan inf norm sub zero) half @ret_only_qnan__extractelement_unknown(<4 x half> %vec, i32 %idx) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) half @ret_only_qnan__extractelement_unknown(
; CHECK-SAME: <4 x half> [[VEC:%.*]], i32 [[IDX:%.*]]) {
-; CHECK-NEXT: [[EXT:%.*]] = extractelement <4 x half> [[VEC]], i32 [[IDX]]
-; CHECK-NEXT: ret half [[EXT]]
+; CHECK-NEXT: ret half 0xH7E00
;
%ext = extractelement <4 x half> %vec, i32 %idx
ret half %ext
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fadd.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fadd.ll
index 02a4fa5b52d10..ec13a1c113d15 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fadd.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fadd.ll
@@ -43,8 +43,7 @@ define nofpclass(inf zero sub norm) half @ret_only_nan(half %x, half %y) {
define nofpclass(snan inf zero sub norm) half @ret_only_qnan(half %x, half %y) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) half @ret_only_qnan(
; CHECK-SAME: half [[X:%.*]], half [[Y:%.*]]) {
-; CHECK-NEXT: [[ADD:%.*]] = fadd half [[X]], [[Y]]
-; CHECK-NEXT: ret half [[ADD]]
+; CHECK-NEXT: ret half 0xH7E00
;
%add = fadd half %x, %y
ret half %add
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fmul.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fmul.ll
index 4ed2e781a30d5..b5ad0ad4cafe3 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fmul.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fmul.ll
@@ -112,8 +112,7 @@ define nofpclass(inf norm sub zero) float @ret_only_nan_results_square(float nou
define nofpclass(inf norm sub zero snan) float @ret_only_qnan_results_square(float noundef %x) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) float @ret_only_qnan_results_square(
; CHECK-SAME: float noundef [[X:%.*]]) {
-; CHECK-NEXT: [[MUL:%.*]] = fmul float [[X]], [[X]]
-; CHECK-NEXT: ret float [[MUL]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%mul = fmul float %x, %x
ret float %mul
@@ -885,8 +884,7 @@ define nofpclass(inf norm sub zero) float @ret_only_nan_results_fmul(float %x, f
define nofpclass(inf norm sub zero snan) float @ret_only_qnan_results_fmul(float %x, float %y) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) float @ret_only_qnan_results_fmul(
; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
-; CHECK-NEXT: [[MUL:%.*]] = fmul float [[X]], [[Y]]
-; CHECK-NEXT: ret float [[MUL]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%mul = fmul float %x, %y
ret float %mul
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fpext.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fpext.ll
index c1070954a26ff..7334277750d7e 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fpext.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fpext.ll
@@ -36,8 +36,7 @@ define nofpclass(inf norm sub zero qnan) float @ret_only_snan__fpext(half %x) {
define nofpclass(inf norm sub zero snan) float @ret_only_qnan__fpext(half %x) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) float @ret_only_qnan__fpext(
; CHECK-SAME: half [[X:%.*]]) {
-; CHECK-NEXT: [[RESULT:%.*]] = fpext half [[X]] to float
-; CHECK-NEXT: ret float [[RESULT]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%result = fpext half %x to float
ret float %result
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fptrunc-round.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fptrunc-round.ll
index 9ca3956be5358..33fe7977701ab 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fptrunc-round.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fptrunc-round.ll
@@ -40,8 +40,7 @@ define nofpclass(inf norm sub zero qnan) half @ret_only_snan__fptrunc(float %x)
define nofpclass(inf norm sub zero snan) half @ret_only_qnan__fptrunc(float %x) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) half @ret_only_qnan__fptrunc(
; CHECK-SAME: float [[X:%.*]]) {
-; CHECK-NEXT: [[RESULT:%.*]] = call half @llvm.fptrunc.round.f16.f32(float [[X]], metadata !"round.downward")
-; CHECK-NEXT: ret half [[RESULT]]
+; CHECK-NEXT: ret half 0xH7E00
;
%result = call half @llvm.fptrunc.round.f16.f32(float %x, metadata !"round.downward")
ret half %result
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fptrunc.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fptrunc.ll
index c1d5dacbc26c9..2edb04956d407 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fptrunc.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-fptrunc.ll
@@ -40,8 +40,7 @@ define nofpclass(inf norm sub zero qnan) half @ret_only_snan__fptrunc(float %x)
define nofpclass(inf norm sub zero snan) half @ret_only_qnan__fptrunc(float %x) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) half @ret_only_qnan__fptrunc(
; CHECK-SAME: float [[X:%.*]]) {
-; CHECK-NEXT: [[RESULT:%.*]] = fptrunc float [[X]] to half
-; CHECK-NEXT: ret half [[RESULT]]
+; CHECK-NEXT: ret half 0xH7E00
;
%result = fptrunc float %x to half
ret half %result
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-frexp.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-frexp.ll
index dc9c00ef15461..f4e7478dad5a1 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-frexp.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-frexp.ll
@@ -65,7 +65,7 @@ define nofpclass(nan) half @extractvalue_not_frexp() {
define nofpclass(snan inf norm sub zero) half @ret_only_qnan__frexp(half %unknown) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) half @ret_only_qnan__frexp(
; CHECK-SAME: half [[UNKNOWN:%.*]]) {
-; CHECK-NEXT: ret half [[UNKNOWN]]
+; CHECK-NEXT: ret half 0xH7E00
;
%frexp = call { half, i32 } @llvm.frexp.f16.i32(half %unknown)
%frexp.mant = extractvalue { half, i32 } %frexp, 0
@@ -316,8 +316,7 @@ define nofpclass(qnan) half @ret_nofpclass_qnan__frexp_select_unknown_qnan(i1 %c
; CHECK-LABEL: define nofpclass(qnan) half @ret_nofpclass_qnan__frexp_select_unknown_qnan(
; CHECK-SAME: i1 [[COND:%.*]], half [[UNKNOWN:%.*]]) {
; CHECK-NEXT: [[ONLY_QNAN:%.*]] = call half @returns_qnan()
-; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[COND]], half [[UNKNOWN]], half [[ONLY_QNAN]]
-; CHECK-NEXT: [[FREXP:%.*]] = call { half, i32 } @llvm.frexp.f16.i32(half [[SELECT]])
+; CHECK-NEXT: [[FREXP:%.*]] = call { half, i32 } @llvm.frexp.f16.i32(half [[UNKNOWN]])
; CHECK-NEXT: [[FREXP_MANT:%.*]] = extractvalue { half, i32 } [[FREXP]], 0
; CHECK-NEXT: ret half [[FREXP_MANT]]
;
@@ -533,7 +532,7 @@ define nofpclass(snan) half @src_only_inf__frexp() {
define nofpclass(snan) half @src_only_nan__frexp() {
; CHECK-LABEL: define nofpclass(snan) half @src_only_nan__frexp() {
; CHECK-NEXT: [[ONLY_NAN:%.*]] = call half @returns_nan()
-; CHECK-NEXT: ret half [[ONLY_NAN]]
+; CHECK-NEXT: ret half 0xH7E00
;
%only.nan = call half @returns_nan()
%frexp = call { half, i32 } @llvm.frexp.f16.i32(half %only.nan)
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-insertelement.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-insertelement.ll
index 36d8766d967aa..8c6679d8be038 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-insertelement.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-insertelement.ll
@@ -29,8 +29,7 @@ define nofpclass(qnan inf zero sub norm) <4 x half> @ret_only_snan__insert_unkno
define nofpclass(snan inf zero sub norm) <4 x half> @ret_only_qnan__insert_unknown_unknown(<4 x half> %vec, half %elt, i32 %idx) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) <4 x half> @ret_only_qnan__insert_unknown_unknown(
; CHECK-SAME: <4 x half> [[VEC:%.*]], half [[ELT:%.*]], i32 [[IDX:%.*]]) {
-; CHECK-NEXT: [[INSERT:%.*]] = insertelement <4 x half> [[VEC]], half [[ELT]], i32 [[IDX]]
-; CHECK-NEXT: ret <4 x half> [[INSERT]]
+; CHECK-NEXT: ret <4 x half> splat (half 0xH7E00)
;
%insert = insertelement <4 x half> %vec, half %elt, i32 %idx
ret <4 x half> %insert
@@ -160,7 +159,7 @@ define nofpclass(snan) <4 x half> @insert_unknown_taints_known_nan_vector_input(
; CHECK-LABEL: define nofpclass(snan) <4 x half> @insert_unknown_taints_known_nan_vector_input(
; CHECK-SAME: half [[UNKNOWN_ELT:%.*]], i32 [[IDX:%.*]]) {
; CHECK-NEXT: [[NAN_VEC:%.*]] = call <4 x half> @returns_nan()
-; CHECK-NEXT: [[INSERT:%.*]] = insertelement <4 x half> [[NAN_VEC]], half [[UNKNOWN_ELT]], i32 [[IDX]]
+; CHECK-NEXT: [[INSERT:%.*]] = insertelement <4 x half> splat (half 0xH7E00), half [[UNKNOWN_ELT]], i32 [[IDX]]
; CHECK-NEXT: [[EXP:%.*]] = call <4 x half> @llvm.exp.v4f16(<4 x half> [[INSERT]])
; CHECK-NEXT: ret <4 x half> [[EXP]]
;
@@ -175,7 +174,7 @@ define nofpclass(snan) <4 x half> @insert_unknown_vector_taints_known_nan_vector
; CHECK-LABEL: define nofpclass(snan) <4 x half> @insert_unknown_vector_taints_known_nan_vector_insert(
; CHECK-SAME: <4 x half> [[UNKNOWN_VEC:%.*]], i32 [[IDX:%.*]]) {
; CHECK-NEXT: [[NAN_ELT:%.*]] = call half @returns_nan_f16()
-; CHECK-NEXT: [[INSERT:%.*]] = insertelement <4 x half> [[UNKNOWN_VEC]], half [[NAN_ELT]], i32 [[IDX]]
+; CHECK-NEXT: [[INSERT:%.*]] = insertelement <4 x half> [[UNKNOWN_VEC]], half 0xH7E00, i32 [[IDX]]
; CHECK-NEXT: [[EXP:%.*]] = call <4 x half> @llvm.exp.v4f16(<4 x half> [[INSERT]])
; CHECK-NEXT: ret <4 x half> [[EXP]]
;
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-maximum.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-maximum.ll
index 4c0f2f9d7ae78..b6a6e63af8acb 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-maximum.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-maximum.ll
@@ -68,8 +68,7 @@ define nofpclass(inf norm sub zero qnan) float @ret_only_snan(float %x, float %y
define nofpclass(inf norm sub zero snan) float @ret_only_qnan(float %x, float %y) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) float @ret_only_qnan(
; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
-; CHECK-NEXT: [[RESULT:%.*]] = call nsz float @llvm.maximum.f32(float [[X]], float [[Y]])
-; CHECK-NEXT: ret float [[RESULT]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%result = call float @llvm.maximum.f32(float %x, float %y)
ret float %result
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-maximumnum.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-maximumnum.ll
index 4c87ca17a3512..2589d80a256d6 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-maximumnum.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-maximumnum.ll
@@ -67,8 +67,7 @@ define nofpclass(inf norm sub zero qnan) float @ret_only_snan(float %x, float %y
define nofpclass(inf norm sub zero snan) float @ret_only_qnan(float %x, float %y) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) float @ret_only_qnan(
; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
-; CHECK-NEXT: [[RESULT:%.*]] = call nsz float @llvm.maximumnum.f32(float [[X]], float [[Y]])
-; CHECK-NEXT: ret float [[RESULT]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%result = call float @llvm.maximumnum.f32(float %x, float %y)
ret float %result
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-minimum.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-minimum.ll
index e62ec503c78ab..fba6e9c45da4d 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-minimum.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-minimum.ll
@@ -67,8 +67,7 @@ define nofpclass(inf norm sub zero qnan) float @ret_only_snan(float %x, float %y
define nofpclass(inf norm sub zero snan) float @ret_only_qnan(float %x, float %y) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) float @ret_only_qnan(
; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
-; CHECK-NEXT: [[RESULT:%.*]] = call nsz float @llvm.minimum.f32(float [[X]], float [[Y]])
-; CHECK-NEXT: ret float [[RESULT]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%result = call float @llvm.minimum.f32(float %x, float %y)
ret float %result
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-minimumnum.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-minimumnum.ll
index e66e3afb52c77..b67077cb7dbd9 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-minimumnum.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-minimumnum.ll
@@ -67,8 +67,7 @@ define nofpclass(inf norm sub zero qnan) float @ret_only_snan(float %x, float %y
define nofpclass(inf norm sub zero snan) float @ret_only_qnan(float %x, float %y) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) float @ret_only_qnan(
; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
-; CHECK-NEXT: [[RESULT:%.*]] = call nsz float @llvm.minimumnum.f32(float [[X]], float [[Y]])
-; CHECK-NEXT: ret float [[RESULT]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%result = call float @llvm.minimumnum.f32(float %x, float %y)
ret float %result
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-rounding-intrinsics.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-rounding-intrinsics.ll
index 1d8a08170677f..d1642569c6610 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-rounding-intrinsics.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-rounding-intrinsics.ll
@@ -42,8 +42,7 @@ define nofpclass(inf norm sub zero qnan) float @ret_only_snan__floor(float %x) {
define nofpclass(inf norm sub zero snan) float @ret_only_qnan__floor(float %x) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) float @ret_only_qnan__floor(
; CHECK-SAME: float [[X:%.*]]) {
-; CHECK-NEXT: [[RESULT:%.*]] = call float @llvm.floor.f32(float [[X]])
-; CHECK-NEXT: ret float [[RESULT]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%result = call float @llvm.floor.f32(float %x)
ret float %result
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-shufflevector.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-shufflevector.ll
index ee8be3ca1bf89..565e9b76ddea3 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-shufflevector.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-shufflevector.ll
@@ -28,8 +28,7 @@ define nofpclass(qnan inf zero sub norm) <4 x half> @ret_only_snan__shufflevecto
define nofpclass(snan inf zero sub norm) <4 x half> @ret_only_qnan__shufflevector_unknown(<4 x half> %vec0, <4 x half> %vec1) {
; CHECK-LABEL: define nofpclass(snan inf zero sub norm) <4 x half> @ret_only_qnan__shufflevector_unknown(
; CHECK-SAME: <4 x half> [[VEC0:%.*]], <4 x half> [[VEC1:%.*]]) {
-; CHECK-NEXT: [[SHUFFLE:%.*]] = shufflevector <4 x half> [[VEC0]], <4 x half> [[VEC1]], <4 x i32> <i32 6, i32 2, i32 3, i32 0>
-; CHECK-NEXT: ret <4 x half> [[SHUFFLE]]
+; CHECK-NEXT: ret <4 x half> splat (half 0xH7E00)
;
%shuffle = shufflevector <4 x half> %vec0, <4 x half> %vec1, <4 x i32> <i32 6, i32 2, i32 3, i32 0>
ret <4 x half> %shuffle
@@ -242,7 +241,7 @@ define nofpclass(snan) <4 x half> @ret_nonnan_rhs_taints_known_nan_result(i1 %co
; CHECK-LABEL: define nofpclass(snan) <4 x half> @ret_nonnan_rhs_taints_known_nan_result(
; CHECK-SAME: i1 [[COND:%.*]], <4 x half> [[UNKNOWN:%.*]]) {
; CHECK-NEXT: [[NAN:%.*]] = call <4 x half> @returns_nan()
-; CHECK-NEXT: [[SHUFFLE:%.*]] = shufflevector <4 x half> [[NAN]], <4 x half> [[UNKNOWN]], <4 x i32> <i32 5, i32 0, i32 1, i32 3>
+; CHECK-NEXT: [[SHUFFLE:%.*]] = shufflevector <4 x half> <half 0xH7E00, half 0xH7E00, half poison, half 0xH7E00>, <4 x half> [[UNKNOWN]], <4 x i32> <i32 5, i32 0, i32 1, i32 3>
; CHECK-NEXT: [[EXP:%.*]] = call <4 x half> @llvm.exp.v4f16(<4 x half> [[SHUFFLE]])
; CHECK-NEXT: ret <4 x half> [[EXP]]
;
@@ -257,7 +256,7 @@ define nofpclass(snan) <4 x half> @ret_nonnan_lhs_taints_known_nan_result(i1 %co
; CHECK-LABEL: define nofpclass(snan) <4 x half> @ret_nonnan_lhs_taints_known_nan_result(
; CHECK-SAME: i1 [[COND:%.*]], <4 x half> [[UNKNOWN:%.*]]) {
; CHECK-NEXT: [[NAN:%.*]] = call <4 x half> @returns_nan()
-; CHECK-NEXT: [[SHUFFLE:%.*]] = shufflevector <4 x half> [[UNKNOWN]], <4 x half> [[NAN]], <4 x i32> <i32 5, i32 0, i32 1, i32 3>
+; CHECK-NEXT: [[SHUFFLE:%.*]] = shufflevector <4 x half> [[UNKNOWN]], <4 x half> <half poison, half 0xH7E00, half poison, half poison>, <4 x i32> <i32 5, i32 0, i32 1, i32 3>
; CHECK-NEXT: [[EXP:%.*]] = call <4 x half> @llvm.exp.v4f16(<4 x half> [[SHUFFLE]])
; CHECK-NEXT: ret <4 x half> [[EXP]]
;
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-sqrt.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-sqrt.ll
index b09faf0f4c3af..0520fef0f0e79 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-sqrt.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-sqrt.ll
@@ -163,9 +163,7 @@ define nofpclass(inf norm zero) float @ret_only_nan_or_sub__sqrt__select_unknown
; CHECK-LABEL: define nofpclass(inf zero norm) float @ret_only_nan_or_sub__sqrt__select_unknown_or_maybe_ninf(
; CHECK-SAME: i1 [[COND:%.*]], float nofpclass(nan) [[X:%.*]]) {
; CHECK-NEXT: [[MAYBE_NINF:%.*]] = call nofpclass(nan pinf sub norm) float @func()
-; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[COND]], float [[X]], float 0xFFF0000000000000
-; CHECK-NEXT: [[RESULT:%.*]] = call float @llvm.sqrt.f32(float [[SELECT]])
-; CHECK-NEXT: ret float [[RESULT]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%maybe.ninf = call nofpclass(pinf norm sub nan) float @func()
%select = select i1 %cond, float %x, float %maybe.ninf
@@ -178,9 +176,7 @@ define nofpclass(inf norm zero) float @ret_only_nan_or_sub__sqrt__select_unknown
; CHECK-LABEL: define nofpclass(inf zero norm) float @ret_only_nan_or_sub__sqrt__select_unknown_or_maybe_nnorm(
; CHECK-SAME: i1 [[COND:%.*]], float nofpclass(nan) [[X:%.*]]) {
; CHECK-NEXT: [[MAYBE_NNORM:%.*]] = call nofpclass(nan inf sub pnorm) float @func()
-; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[COND]], float [[X]], float [[MAYBE_NNORM]]
-; CHECK-NEXT: [[RESULT:%.*]] = call float @llvm.sqrt.f32(float [[SELECT]])
-; CHECK-NEXT: ret float [[RESULT]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%maybe.nnorm = call nofpclass(inf pnorm sub nan) float @func()
%select = select i1 %cond, float %x, float %maybe.nnorm
@@ -193,9 +189,7 @@ define nofpclass(inf norm zero) float @ret_only_nan_or_sub__sqrt__select_unknown
; CHECK-LABEL: define nofpclass(inf zero norm) float @ret_only_nan_or_sub__sqrt__select_unknown_or_maybe_nsub(
; CHECK-SAME: i1 [[COND:%.*]], float nofpclass(nan) [[X:%.*]]) {
; CHECK-NEXT: [[MAYBE_NSUB:%.*]] = call nofpclass(nan inf psub norm) float @func()
-; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[COND]], float [[X]], float [[MAYBE_NSUB]]
-; CHECK-NEXT: [[RESULT:%.*]] = call float @llvm.sqrt.f32(float [[SELECT]])
-; CHECK-NEXT: ret float [[RESULT]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%maybe.nsub = call nofpclass(inf norm psub nan) float @func()
%select = select i1 %cond, float %x, float %maybe.nsub
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
index 714e4ff4398e2..359fb83c35123 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
@@ -1348,7 +1348,7 @@ define nofpclass(snan) float @ret_nofpclass_snan__nofpclass_call_only_nan(i1 %co
; CHECK-LABEL: define nofpclass(snan) float @ret_nofpclass_snan__nofpclass_call_only_nan
; CHECK-SAME: (i1 [[COND:%.*]], float [[Y:%.*]]) {
; CHECK-NEXT: [[MUST_BE_NAN:%.*]] = call nofpclass(inf zero sub norm) float @extern()
-; CHECK-NEXT: ret float [[MUST_BE_NAN]]
+; CHECK-NEXT: ret float 0x7FF8000000000000
;
%must.be.nan = call nofpclass(inf norm zero sub) float @extern()
ret float %must.be.nan
>From 82df18e71079685d44c6b798ad4e0bd6f0519503 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Thu, 15 Jan 2026 17:26:57 +0100
Subject: [PATCH 2/3] Move isAggregateType, although this can't break for any
existing case
---
.../InstCombine/InstCombineSimplifyDemanded.cpp | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index de1da8acae47a..13cb833145c43 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -2013,14 +2013,14 @@ static Constant *getFPClassConstant(Type *Ty, FPClassTest Mask,
if (Mask == fcPosZero)
return Constant::getNullValue(Ty);
- // Turn any possible snans into quiet if we can.
- if (Mask == fcNan && IsCanonicalizing)
- return ConstantFP::getQNaN(Ty);
-
// TODO: Support aggregate types that are allowed by FPMathOperator.
if (Ty->isAggregateType())
return nullptr;
+ // Turn any possible snans into quiet if we can.
+ if (Mask == fcNan && IsCanonicalizing)
+ return ConstantFP::getQNaN(Ty);
+
switch (Mask) {
case fcNegZero:
return ConstantFP::getZero(Ty, true);
>From 71687bac95f1d00a516f106959b83794daa60000 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Thu, 15 Jan 2026 17:24:36 +0100
Subject: [PATCH 3/3] Check IsCanonicalizing
---
.../InstCombineSimplifyDemanded.cpp | 3 +-
.../InstCombine/simplify-demanded-fpclass.ll | 86 ++++++++++++++++++-
2 files changed, 87 insertions(+), 2 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 13cb833145c43..369bd561f674c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -2029,7 +2029,8 @@ static Constant *getFPClassConstant(Type *Ty, FPClassTest Mask,
case fcNegInf:
return ConstantFP::getInfinity(Ty, true);
case fcQNan:
- return ConstantFP::getQNaN(Ty);
+ // Payload bits cannot be dropped for pure signbit operations.
+ return IsCanonicalizing ? ConstantFP::getQNaN(Ty) : nullptr;
default:
return nullptr;
}
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
index 359fb83c35123..4761569200770 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
@@ -485,6 +485,90 @@ define nofpclass(inf) float @ret_nofpclass_inf__select_chain_inf_nan_1(i1 %cond,
ret float %select1
}
+define nofpclass(inf norm sub zero) float @ret_only_nan__fabs(float %unknown) {
+; CHECK-LABEL: define nofpclass(inf zero sub norm) float @ret_only_nan__fabs
+; CHECK-SAME: (float [[UNKNOWN:%.*]]) {
+; CHECK-NEXT: [[FABS:%.*]] = call float @llvm.fabs.f32(float [[UNKNOWN]])
+; CHECK-NEXT: ret float [[FABS]]
+;
+ %fabs = call float @llvm.fabs.f32(float %unknown)
+ ret float %fabs
+}
+
+define nofpclass(snan inf norm sub zero) float @ret_only_qnan__fabs(float %unknown) {
+; CHECK-LABEL: define nofpclass(snan inf zero sub norm) float @ret_only_qnan__fabs
+; CHECK-SAME: (float [[UNKNOWN:%.*]]) {
+; CHECK-NEXT: [[FABS:%.*]] = call float @llvm.fabs.f32(float [[UNKNOWN]])
+; CHECK-NEXT: ret float [[FABS]]
+;
+ %fabs = call float @llvm.fabs.f32(float %unknown)
+ ret float %fabs
+}
+
+define nofpclass(qnan inf norm sub zero) float @ret_only_snan__fabs(float %unknown) {
+; CHECK-LABEL: define nofpclass(qnan inf zero sub norm) float @ret_only_snan__fabs
+; CHECK-SAME: (float [[UNKNOWN:%.*]]) {
+; CHECK-NEXT: [[FABS:%.*]] = call float @llvm.fabs.f32(float [[UNKNOWN]])
+; CHECK-NEXT: ret float [[FABS]]
+;
+ %fabs = call float @llvm.fabs.f32(float %unknown)
+ ret float %fabs
+}
+
+define nofpclass(nan norm sub zero) float @ret_only_inf__fabs(float %unknown) {
+; CHECK-LABEL: define nofpclass(nan zero sub norm) float @ret_only_inf__fabs
+; CHECK-SAME: (float [[UNKNOWN:%.*]]) {
+; CHECK-NEXT: ret float 0x7FF0000000000000
+;
+ %fabs = call float @llvm.fabs.f32(float %unknown)
+ ret float %fabs
+}
+
+define nofpclass(nan ninf norm sub zero) float @ret_only_pinf__fabs(float %unknown) {
+; CHECK-LABEL: define nofpclass(nan ninf zero sub norm) float @ret_only_pinf__fabs
+; CHECK-SAME: (float [[UNKNOWN:%.*]]) {
+; CHECK-NEXT: ret float 0x7FF0000000000000
+;
+ %fabs = call float @llvm.fabs.f32(float %unknown)
+ ret float %fabs
+}
+
+define nofpclass(nan pinf norm sub zero) float @ret_only_ninf__fabs(float %unknown) {
+; CHECK-LABEL: define nofpclass(nan pinf zero sub norm) float @ret_only_ninf__fabs
+; CHECK-SAME: (float [[UNKNOWN:%.*]]) {
+; CHECK-NEXT: ret float poison
+;
+ %fabs = call float @llvm.fabs.f32(float %unknown)
+ ret float %fabs
+}
+
+define nofpclass(nan inf norm sub) float @ret_only_zero__fabs(float %unknown) {
+; CHECK-LABEL: define nofpclass(nan inf sub norm) float @ret_only_zero__fabs
+; CHECK-SAME: (float [[UNKNOWN:%.*]]) {
+; CHECK-NEXT: ret float 0.000000e+00
+;
+ %fabs = call float @llvm.fabs.f32(float %unknown)
+ ret float %fabs
+}
+
+define nofpclass(nan inf norm sub pzero) float @ret_only_nzero__fabs(float %unknown) {
+; CHECK-LABEL: define nofpclass(nan inf pzero sub norm) float @ret_only_nzero__fabs
+; CHECK-SAME: (float [[UNKNOWN:%.*]]) {
+; CHECK-NEXT: ret float poison
+;
+ %fabs = call float @llvm.fabs.f32(float %unknown)
+ ret float %fabs
+}
+
+define nofpclass(nan inf norm sub nzero) float @ret_only_pzero__fabs(float %unknown) {
+; CHECK-LABEL: define nofpclass(nan inf nzero sub norm) float @ret_only_pzero__fabs
+; CHECK-SAME: (float [[UNKNOWN:%.*]]) {
+; CHECK-NEXT: ret float 0.000000e+00
+;
+ %fabs = call float @llvm.fabs.f32(float %unknown)
+ ret float %fabs
+}
+
; Simplify to fabs %x
define nofpclass(inf) float @ret_nofpclass_inf__fabs_select_ninf_rhs(i1 %cond, float %x) {
; CHECK-LABEL: define nofpclass(inf) float @ret_nofpclass_inf__fabs_select_ninf_rhs
@@ -1348,7 +1432,7 @@ define nofpclass(snan) float @ret_nofpclass_snan__nofpclass_call_only_nan(i1 %co
; CHECK-LABEL: define nofpclass(snan) float @ret_nofpclass_snan__nofpclass_call_only_nan
; CHECK-SAME: (i1 [[COND:%.*]], float [[Y:%.*]]) {
; CHECK-NEXT: [[MUST_BE_NAN:%.*]] = call nofpclass(inf zero sub norm) float @extern()
-; CHECK-NEXT: ret float 0x7FF8000000000000
+; CHECK-NEXT: ret float [[MUST_BE_NAN]]
;
%must.be.nan = call nofpclass(inf norm zero sub) float @extern()
ret float %must.be.nan
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