[clang] [llvm] [ValueTracking] Teach isGuaranteedNotToBeUndefOrPoison about splats (PR #163570)
Cullen Rhodes via cfe-commits
cfe-commits at lists.llvm.org
Thu Oct 16 01:03:28 PDT 2025
https://github.com/c-rhodes updated https://github.com/llvm/llvm-project/pull/163570
>From c8cdc8c3294453039059dcf4f8340d02f42a4e32 Mon Sep 17 00:00:00 2001
From: Cullen Rhodes <cullen.rhodes at arm.com>
Date: Fri, 10 Oct 2025 14:22:45 +0000
Subject: [PATCH 1/3] [ValueTracking] Teach isGuaranteedNotToBeUndefOrPoison
about splats
Splats include two poison values, but only the poison-ness of the
splatted value actually matters.
---
llvm/lib/Analysis/ValueTracking.cpp | 5 +++++
llvm/unittests/Analysis/ValueTrackingTest.cpp | 10 ++++++++++
2 files changed, 15 insertions(+)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 9655c886f4441..b0016c36bf5da 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -7678,6 +7678,7 @@ static bool isGuaranteedNotToBeUndefOrPoison(
return true;
}
+ Value *Splat;
if (!::canCreateUndefOrPoison(Opr, Kind,
/*ConsiderFlagsAndMetadata=*/true)) {
if (const auto *PN = dyn_cast<PHINode>(V)) {
@@ -7695,6 +7696,10 @@ static bool isGuaranteedNotToBeUndefOrPoison(
}
if (IsWellDefined)
return true;
+ } else if (isa<ShuffleVectorInst>(Opr) && (Splat = getSplatValue(Opr))) {
+ // For splats we only need to check the value being splatted.
+ if (OpCheck(Splat))
+ return true;
} else if (all_of(Opr->operands(), OpCheck))
return true;
}
diff --git a/llvm/unittests/Analysis/ValueTrackingTest.cpp b/llvm/unittests/Analysis/ValueTrackingTest.cpp
index 559a0b724f383..bb0280ee69cfd 100644
--- a/llvm/unittests/Analysis/ValueTrackingTest.cpp
+++ b/llvm/unittests/Analysis/ValueTrackingTest.cpp
@@ -1091,6 +1091,16 @@ TEST_F(ValueTrackingTest, isGuaranteedNotToBeUndefOrPoison) {
}
}
+TEST_F(ValueTrackingTest, isGuaranteedNotToBeUndefOrPoison_splat) {
+ parseAssembly(
+ "define <4 x i32> @test(i32 noundef %x) {\n"
+ " %ins = insertelement <4 x i32> poison, i32 %x, i32 0\n"
+ " %A = shufflevector <4 x i32> %ins, <4 x i32> poison, <4 x i32> zeroinitializer\n"
+ " ret <4 x i32> %A\n"
+ "}");
+ EXPECT_TRUE(isGuaranteedNotToBeUndefOrPoison(A));
+}
+
TEST_F(ValueTrackingTest, isGuaranteedNotToBeUndefOrPoison_assume) {
parseAssembly("declare i1 @f_i1()\n"
"declare i32 @f_i32()\n"
>From ec522636a0dc3efb52c62be26a0a7f77caee963a Mon Sep 17 00:00:00 2001
From: Cullen Rhodes <cullen.rhodes at arm.com>
Date: Wed, 15 Oct 2025 15:31:11 +0000
Subject: [PATCH 2/3] address comments
---
llvm/lib/Analysis/ValueTracking.cpp | 2 +-
llvm/test/Transforms/InstSimplify/freeze-noundef.ll | 13 +++++++++++++
2 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index b0016c36bf5da..0b65a5a6ed96c 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -7678,9 +7678,9 @@ static bool isGuaranteedNotToBeUndefOrPoison(
return true;
}
- Value *Splat;
if (!::canCreateUndefOrPoison(Opr, Kind,
/*ConsiderFlagsAndMetadata=*/true)) {
+ Value *Splat;
if (const auto *PN = dyn_cast<PHINode>(V)) {
unsigned Num = PN->getNumIncomingValues();
bool IsWellDefined = true;
diff --git a/llvm/test/Transforms/InstSimplify/freeze-noundef.ll b/llvm/test/Transforms/InstSimplify/freeze-noundef.ll
index e6c296994cf6a..de1c2cc74240a 100644
--- a/llvm/test/Transforms/InstSimplify/freeze-noundef.ll
+++ b/llvm/test/Transforms/InstSimplify/freeze-noundef.ll
@@ -156,3 +156,16 @@ define {i8, i32} @noundef_metadata2(ptr %p) {
%v.fr = freeze {i8, i32} %v
ret {i8, i32} %v.fr
}
+
+; For splats only the poison-ness of the value being splatted matters.
+define <4 x i32> @splat(i32 noundef %x) {
+; CHECK-LABEL: @splat(
+; CHECK-NEXT: [[INS:%.*]] = insertelement <4 x i32> poison, i32 [[X:%.*]], i32 0
+; CHECK-NEXT: [[SPLAT:%.*]] = shufflevector <4 x i32> [[INS]], <4 x i32> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT: ret <4 x i32> [[SPLAT]]
+;
+ %ins = insertelement <4 x i32> poison, i32 %x, i32 0
+ %splat = shufflevector <4 x i32> %ins, <4 x i32> poison, <4 x i32> zeroinitializer
+ %splat.fr = freeze <4 x i32> %splat
+ ret <4 x i32> %splat.fr
+}
>From 6cfa5ae70ed2538990af73d3536d9eeb26d44161 Mon Sep 17 00:00:00 2001
From: Cullen Rhodes <cullen.rhodes at arm.com>
Date: Thu, 16 Oct 2025 07:50:38 +0000
Subject: [PATCH 3/3] address comments
---
clang/test/CodeGen/arm-mve-intrinsics/dup.c | 24 +++++++------------
clang/test/Headers/wasm.c | 18 +++++++-------
.../Transforms/InstSimplify/freeze-noundef.ll | 16 ++++++++++++-
3 files changed, 32 insertions(+), 26 deletions(-)
diff --git a/clang/test/CodeGen/arm-mve-intrinsics/dup.c b/clang/test/CodeGen/arm-mve-intrinsics/dup.c
index c2c7a9c278f67..e7113fdcba90a 100644
--- a/clang/test/CodeGen/arm-mve-intrinsics/dup.c
+++ b/clang/test/CodeGen/arm-mve-intrinsics/dup.c
@@ -244,8 +244,7 @@ uint32x4_t test_vdupq_m_n_u32(uint32x4_t inactive, uint32_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <8 x i1> @llvm.arm.mve.pred.i2v.v8i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <8 x half> poison, half [[A:%.*]], i64 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <8 x half> [[DOTSPLATINSERT]], <8 x half> poison, <8 x i32> zeroinitializer
-// CHECK-NEXT: [[TMP2:%.*]] = select <8 x i1> [[TMP1]], <8 x half> [[DOTSPLAT]], <8 x half> undef
-// CHECK-NEXT: ret <8 x half> [[TMP2]]
+// CHECK-NEXT: ret <8 x half> [[DOTSPLAT]]
//
float16x8_t test_vdupq_x_n_f16(float16_t a, mve_pred16_t p)
{
@@ -258,8 +257,7 @@ float16x8_t test_vdupq_x_n_f16(float16_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <4 x i1> @llvm.arm.mve.pred.i2v.v4i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <4 x float> poison, float [[A:%.*]], i64 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <4 x float> [[DOTSPLATINSERT]], <4 x float> poison, <4 x i32> zeroinitializer
-// CHECK-NEXT: [[TMP2:%.*]] = select <4 x i1> [[TMP1]], <4 x float> [[DOTSPLAT]], <4 x float> undef
-// CHECK-NEXT: ret <4 x float> [[TMP2]]
+// CHECK-NEXT: ret <4 x float> [[DOTSPLAT]]
//
float32x4_t test_vdupq_x_n_f32(float32_t a, mve_pred16_t p)
{
@@ -272,8 +270,7 @@ float32x4_t test_vdupq_x_n_f32(float32_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <16 x i1> @llvm.arm.mve.pred.i2v.v16i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <16 x i8> poison, i8 [[A:%.*]], i64 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <16 x i8> [[DOTSPLATINSERT]], <16 x i8> poison, <16 x i32> zeroinitializer
-// CHECK-NEXT: [[TMP2:%.*]] = select <16 x i1> [[TMP1]], <16 x i8> [[DOTSPLAT]], <16 x i8> undef
-// CHECK-NEXT: ret <16 x i8> [[TMP2]]
+// CHECK-NEXT: ret <16 x i8> [[DOTSPLAT]]
//
int8x16_t test_vdupq_x_n_s8(int8_t a, mve_pred16_t p)
{
@@ -286,8 +283,7 @@ int8x16_t test_vdupq_x_n_s8(int8_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <8 x i1> @llvm.arm.mve.pred.i2v.v8i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <8 x i16> poison, i16 [[A:%.*]], i64 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <8 x i16> [[DOTSPLATINSERT]], <8 x i16> poison, <8 x i32> zeroinitializer
-// CHECK-NEXT: [[TMP2:%.*]] = select <8 x i1> [[TMP1]], <8 x i16> [[DOTSPLAT]], <8 x i16> undef
-// CHECK-NEXT: ret <8 x i16> [[TMP2]]
+// CHECK-NEXT: ret <8 x i16> [[DOTSPLAT]]
//
int16x8_t test_vdupq_x_n_s16(int16_t a, mve_pred16_t p)
{
@@ -300,8 +296,7 @@ int16x8_t test_vdupq_x_n_s16(int16_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <4 x i1> @llvm.arm.mve.pred.i2v.v4i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <4 x i32> poison, i32 [[A:%.*]], i64 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <4 x i32> [[DOTSPLATINSERT]], <4 x i32> poison, <4 x i32> zeroinitializer
-// CHECK-NEXT: [[TMP2:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[DOTSPLAT]], <4 x i32> undef
-// CHECK-NEXT: ret <4 x i32> [[TMP2]]
+// CHECK-NEXT: ret <4 x i32> [[DOTSPLAT]]
//
int32x4_t test_vdupq_x_n_s32(int32_t a, mve_pred16_t p)
{
@@ -314,8 +309,7 @@ int32x4_t test_vdupq_x_n_s32(int32_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <16 x i1> @llvm.arm.mve.pred.i2v.v16i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <16 x i8> poison, i8 [[A:%.*]], i64 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <16 x i8> [[DOTSPLATINSERT]], <16 x i8> poison, <16 x i32> zeroinitializer
-// CHECK-NEXT: [[TMP2:%.*]] = select <16 x i1> [[TMP1]], <16 x i8> [[DOTSPLAT]], <16 x i8> undef
-// CHECK-NEXT: ret <16 x i8> [[TMP2]]
+// CHECK-NEXT: ret <16 x i8> [[DOTSPLAT]]
//
uint8x16_t test_vdupq_x_n_u8(uint8_t a, mve_pred16_t p)
{
@@ -328,8 +322,7 @@ uint8x16_t test_vdupq_x_n_u8(uint8_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <8 x i1> @llvm.arm.mve.pred.i2v.v8i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <8 x i16> poison, i16 [[A:%.*]], i64 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <8 x i16> [[DOTSPLATINSERT]], <8 x i16> poison, <8 x i32> zeroinitializer
-// CHECK-NEXT: [[TMP2:%.*]] = select <8 x i1> [[TMP1]], <8 x i16> [[DOTSPLAT]], <8 x i16> undef
-// CHECK-NEXT: ret <8 x i16> [[TMP2]]
+// CHECK-NEXT: ret <8 x i16> [[DOTSPLAT]]
//
uint16x8_t test_vdupq_x_n_u16(uint16_t a, mve_pred16_t p)
{
@@ -342,8 +335,7 @@ uint16x8_t test_vdupq_x_n_u16(uint16_t a, mve_pred16_t p)
// CHECK-NEXT: [[TMP1:%.*]] = call <4 x i1> @llvm.arm.mve.pred.i2v.v4i1(i32 [[TMP0]])
// CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <4 x i32> poison, i32 [[A:%.*]], i64 0
// CHECK-NEXT: [[DOTSPLAT:%.*]] = shufflevector <4 x i32> [[DOTSPLATINSERT]], <4 x i32> poison, <4 x i32> zeroinitializer
-// CHECK-NEXT: [[TMP2:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[DOTSPLAT]], <4 x i32> undef
-// CHECK-NEXT: ret <4 x i32> [[TMP2]]
+// CHECK-NEXT: ret <4 x i32> [[DOTSPLAT]]
//
uint32x4_t test_vdupq_x_n_u32(uint32_t a, mve_pred16_t p)
{
diff --git a/clang/test/Headers/wasm.c b/clang/test/Headers/wasm.c
index 7f427ca313ddc..03f20c5988268 100644
--- a/clang/test/Headers/wasm.c
+++ b/clang/test/Headers/wasm.c
@@ -612,7 +612,7 @@ v128_t test_f64x2_const_splat(void) {
return wasm_f64x2_const_splat(42);
}
-// CHECK-LABEL: define hidden <4 x i32> @test_i8x16_splat(
+// CHECK-LABEL: define hidden noundef <4 x i32> @test_i8x16_splat(
// CHECK-SAME: i8 noundef signext [[A:%.*]]) local_unnamed_addr #[[ATTR2]] {
// CHECK-NEXT: [[ENTRY:.*:]]
// CHECK-NEXT: [[VECINIT_I:%.*]] = insertelement <16 x i8> poison, i8 [[A]], i64 0
@@ -624,7 +624,7 @@ v128_t test_i8x16_splat(int8_t a) {
return wasm_i8x16_splat(a);
}
-// CHECK-LABEL: define hidden <4 x i32> @test_u8x16_splat(
+// CHECK-LABEL: define hidden noundef <4 x i32> @test_u8x16_splat(
// CHECK-SAME: i8 noundef zeroext [[A:%.*]]) local_unnamed_addr #[[ATTR2]] {
// CHECK-NEXT: [[ENTRY:.*:]]
// CHECK-NEXT: [[VECINIT_I:%.*]] = insertelement <16 x i8> poison, i8 [[A]], i64 0
@@ -682,7 +682,7 @@ v128_t test_u8x16_replace_lane(v128_t a, uint8_t b) {
return wasm_u8x16_replace_lane(a, 15, b);
}
-// CHECK-LABEL: define hidden <4 x i32> @test_i16x8_splat(
+// CHECK-LABEL: define hidden noundef <4 x i32> @test_i16x8_splat(
// CHECK-SAME: i16 noundef signext [[A:%.*]]) local_unnamed_addr #[[ATTR2]] {
// CHECK-NEXT: [[ENTRY:.*:]]
// CHECK-NEXT: [[VECINIT_I:%.*]] = insertelement <8 x i16> poison, i16 [[A]], i64 0
@@ -694,7 +694,7 @@ v128_t test_i16x8_splat(int16_t a) {
return wasm_i16x8_splat(a);
}
-// CHECK-LABEL: define hidden <4 x i32> @test_u16x8_splat(
+// CHECK-LABEL: define hidden noundef <4 x i32> @test_u16x8_splat(
// CHECK-SAME: i16 noundef zeroext [[A:%.*]]) local_unnamed_addr #[[ATTR2]] {
// CHECK-NEXT: [[ENTRY:.*:]]
// CHECK-NEXT: [[VECINIT_I:%.*]] = insertelement <8 x i16> poison, i16 [[A]], i64 0
@@ -752,7 +752,7 @@ v128_t test_u16x8_replace_lane(v128_t a, uint16_t b) {
return wasm_u16x8_replace_lane(a, 7, b);
}
-// CHECK-LABEL: define hidden <4 x i32> @test_i32x4_splat(
+// CHECK-LABEL: define hidden noundef <4 x i32> @test_i32x4_splat(
// CHECK-SAME: i32 noundef [[A:%.*]]) local_unnamed_addr #[[ATTR2]] {
// CHECK-NEXT: [[ENTRY:.*:]]
// CHECK-NEXT: [[VECINIT_I:%.*]] = insertelement <4 x i32> poison, i32 [[A]], i64 0
@@ -763,7 +763,7 @@ v128_t test_i32x4_splat(int32_t a) {
return wasm_i32x4_splat(a);
}
-// CHECK-LABEL: define hidden <4 x i32> @test_u32x4_splat(
+// CHECK-LABEL: define hidden noundef <4 x i32> @test_u32x4_splat(
// CHECK-SAME: i32 noundef [[A:%.*]]) local_unnamed_addr #[[ATTR2]] {
// CHECK-NEXT: [[ENTRY:.*:]]
// CHECK-NEXT: [[VECINIT_I:%.*]] = insertelement <4 x i32> poison, i32 [[A]], i64 0
@@ -814,7 +814,7 @@ v128_t test_u32x4_replace_lane(v128_t a, uint32_t b) {
return wasm_u32x4_replace_lane(a, 3, b);
}
-// CHECK-LABEL: define hidden <4 x i32> @test_i64x2_splat(
+// CHECK-LABEL: define hidden noundef <4 x i32> @test_i64x2_splat(
// CHECK-SAME: i64 noundef [[A:%.*]]) local_unnamed_addr #[[ATTR2]] {
// CHECK-NEXT: [[ENTRY:.*:]]
// CHECK-NEXT: [[VECINIT_I:%.*]] = insertelement <2 x i64> poison, i64 [[A]], i64 0
@@ -826,7 +826,7 @@ v128_t test_i64x2_splat(int64_t a) {
return wasm_i64x2_splat(a);
}
-// CHECK-LABEL: define hidden <4 x i32> @test_u64x2_splat(
+// CHECK-LABEL: define hidden noundef <4 x i32> @test_u64x2_splat(
// CHECK-SAME: i64 noundef [[A:%.*]]) local_unnamed_addr #[[ATTR2]] {
// CHECK-NEXT: [[ENTRY:.*:]]
// CHECK-NEXT: [[VECINIT_I:%.*]] = insertelement <2 x i64> poison, i64 [[A]], i64 0
@@ -919,7 +919,7 @@ v128_t test_f32x4_replace_lane(v128_t a, float b) {
return wasm_f32x4_replace_lane(a, 3, b);
}
-// CHECK-LABEL: define hidden <4 x i32> @test_f64x2_splat(
+// CHECK-LABEL: define hidden noundef <4 x i32> @test_f64x2_splat(
// CHECK-SAME: double noundef [[A:%.*]]) local_unnamed_addr #[[ATTR2]] {
// CHECK-NEXT: [[ENTRY:.*:]]
// CHECK-NEXT: [[VECINIT_I:%.*]] = insertelement <2 x double> poison, double [[A]], i64 0
diff --git a/llvm/test/Transforms/InstSimplify/freeze-noundef.ll b/llvm/test/Transforms/InstSimplify/freeze-noundef.ll
index de1c2cc74240a..728e813c8c813 100644
--- a/llvm/test/Transforms/InstSimplify/freeze-noundef.ll
+++ b/llvm/test/Transforms/InstSimplify/freeze-noundef.ll
@@ -157,7 +157,8 @@ define {i8, i32} @noundef_metadata2(ptr %p) {
ret {i8, i32} %v.fr
}
-; For splats only the poison-ness of the value being splatted matters.
+; Splats have two poison values but only the poison-ness of the splatted value
+; matters.
define <4 x i32> @splat(i32 noundef %x) {
; CHECK-LABEL: @splat(
; CHECK-NEXT: [[INS:%.*]] = insertelement <4 x i32> poison, i32 [[X:%.*]], i32 0
@@ -169,3 +170,16 @@ define <4 x i32> @splat(i32 noundef %x) {
%splat.fr = freeze <4 x i32> %splat
ret <4 x i32> %splat.fr
}
+
+define <4 x i32> @splat_poison_idx(i32 noundef %x) {
+; CHECK-LABEL: @splat_poison_idx(
+; CHECK-NEXT: [[INS:%.*]] = insertelement <4 x i32> poison, i32 [[X:%.*]], i32 0
+; CHECK-NEXT: [[SPLAT:%.*]] = shufflevector <4 x i32> [[INS]], <4 x i32> poison, <4 x i32> <i32 0, i32 1, i32 2, i32 poison>
+; CHECK-NEXT: [[SPLAT_FR:%.*]] = freeze <4 x i32> [[SPLAT]]
+; CHECK-NEXT: ret <4 x i32> [[SPLAT_FR]]
+;
+ %ins = insertelement <4 x i32> poison, i32 %x, i32 0
+ %splat = shufflevector <4 x i32> %ins, <4 x i32> poison, <4 x i32> <i32 0, i32 1, i32 2, i32 poison>
+ %splat.fr = freeze <4 x i32> %splat
+ ret <4 x i32> %splat.fr
+}
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