[VectorCombine] Add tests for UB issue, remove immediate UB from existing tests. NFC #138395

lukel97 · 2025-05-03T12:45:52Z

This adds a test that exercises the part of scalarizeBinOpOrCmp that produces immediate UB as described in #138095 (comment), but is fortunately currently folded into a correct transform.

I also noticed a bunch of immediate UB in some of the existing tests so this also cleans them up. They should still all be scalarized though.

…ting tests. NFC

llvmbot · 2025-05-03T12:46:26Z

@llvm/pr-subscribers-llvm-transforms

Author: Luke Lau (lukel97)

Changes

This adds a test that exercises the part of scalarizeBinOpOrCmp that produces immediate UB, but is fortunately currently folded into a correct transform.

I also noticed a bunch of immediate UB in some of the existing tests so this also cleans them up. They should still all be scalarized though.

Full diff: https://github.com/llvm/llvm-project/pull/138395.diff

4 Files Affected:

(modified) llvm/test/Transforms/VectorCombine/AArch64/scalarize-scalable.ll (+1-1)
(modified) llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant-inseltpoison.ll (+18-18)
(modified) llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll (+24-24)
(added) llvm/test/Transforms/VectorCombine/binop-scalarize.ll (+22)

diff --git a/llvm/test/Transforms/VectorCombine/AArch64/scalarize-scalable.ll b/llvm/test/Transforms/VectorCombine/AArch64/scalarize-scalable.ll
index ac7bc91fa3f25..6350ce7598a71 100644
--- a/llvm/test/Transforms/VectorCombine/AArch64/scalarize-scalable.ll
+++ b/llvm/test/Transforms/VectorCombine/AArch64/scalarize-scalable.ll
@@ -30,7 +30,7 @@ define <vscale x 4 x i32> @scalarize_scalable_udiv(i32 %x, i32 %y) {
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[R]]
 ;
   %splatx = insertelement <vscale x 4 x i32> poison, i32 %x, i64 0
-  %splaty = insertelement <vscale x 4 x i32> poison, i32 %y, i64 0
+  %splaty = insertelement <vscale x 4 x i32> splat (i32 1), i32 %y, i64 0
   %r = udiv <vscale x 4 x i32> %splatx, %splaty
   ret <vscale x 4 x i32> %r
 }
diff --git a/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant-inseltpoison.ll b/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant-inseltpoison.ll
index 05251cb829b2b..d45d5f4d44ff3 100644
--- a/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant-inseltpoison.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant-inseltpoison.ll
@@ -305,10 +305,10 @@ define <2 x i64> @lshr_constant_op1_not_undef_lane(i64 %x) {
 define <2 x i64> @urem_constant_op0(i64 %x) {
 ; CHECK-LABEL: @urem_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = urem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> poison, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = urem <2 x i64> <i64 5, i64 undef>, %ins
   ret <2 x i64> %bo
 }
@@ -316,10 +316,10 @@ define <2 x i64> @urem_constant_op0(i64 %x) {
 define <2 x i64> @urem_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @urem_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = urem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> poison, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = urem <2 x i64> <i64 5, i64 2>, %ins
   ret <2 x i64> %bo
 }
@@ -331,7 +331,7 @@ define <2 x i64> @urem_constant_op1(i64 %x) {
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> poison, i64 %x, i32 1
-  %bo = urem <2 x i64> %ins, <i64 undef, i64 2>
+  %bo = urem <2 x i64> %ins, <i64 2, i64 2>
   ret <2 x i64> %bo
 }
 
@@ -360,10 +360,10 @@ define <2 x i64> @srem_constant_op0(i64 %x) {
 define <2 x i64> @srem_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @srem_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = srem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> poison, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = srem <2 x i64> <i64 5, i64 2>, %ins
   ret <2 x i64> %bo
 }
@@ -375,7 +375,7 @@ define <2 x i64> @srem_constant_op1(i64 %x) {
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> poison, i64 %x, i32 1
-  %bo = srem <2 x i64> %ins, <i64 undef, i64 2>
+  %bo = srem <2 x i64> %ins, <i64 2, i64 2>
   ret <2 x i64> %bo
 }
 
@@ -393,10 +393,10 @@ define <2 x i64> @srem_constant_op1_not_undef_lane(i64 %x) {
 define <2 x i64> @udiv_constant_op0(i64 %x) {
 ; CHECK-LABEL: @udiv_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = udiv exact i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 5, i64 undef>, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> poison, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = udiv exact <2 x i64> <i64 5, i64 undef>, %ins
   ret <2 x i64> %bo
 }
@@ -404,10 +404,10 @@ define <2 x i64> @udiv_constant_op0(i64 %x) {
 define <2 x i64> @udiv_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @udiv_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = udiv exact i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 5, i64 2>, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> poison, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = udiv exact <2 x i64> <i64 5, i64 2>, %ins
   ret <2 x i64> %bo
 }
@@ -419,7 +419,7 @@ define <2 x i64> @udiv_constant_op1(i64 %x) {
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> poison, i64 %x, i32 1
-  %bo = udiv <2 x i64> %ins, <i64 undef, i64 2>
+  %bo = udiv <2 x i64> %ins, <i64 2, i64 2>
   ret <2 x i64> %bo
 }
 
@@ -437,10 +437,10 @@ define <2 x i64> @udiv_constant_op1_not_undef_lane(i64 %x) {
 define <2 x i64> @sdiv_constant_op0(i64 %x) {
 ; CHECK-LABEL: @sdiv_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = sdiv i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 5, i64 undef>, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> poison, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = sdiv <2 x i64> <i64 5, i64 undef>, %ins
   ret <2 x i64> %bo
 }
@@ -448,10 +448,10 @@ define <2 x i64> @sdiv_constant_op0(i64 %x) {
 define <2 x i64> @sdiv_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @sdiv_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = sdiv i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 5, i64 2>, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> poison, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = sdiv <2 x i64> <i64 5, i64 2>, %ins
   ret <2 x i64> %bo
 }
@@ -463,7 +463,7 @@ define <2 x i64> @sdiv_constant_op1(i64 %x) {
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> poison, i64 %x, i32 1
-  %bo = sdiv exact <2 x i64> %ins, <i64 undef, i64 2>
+  %bo = sdiv exact <2 x i64> %ins, <i64 2, i64 2>
   ret <2 x i64> %bo
 }
 
diff --git a/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll b/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll
index bbdd76c58b58e..2b5a58ea44de4 100644
--- a/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll
@@ -305,10 +305,10 @@ define <2 x i64> @lshr_constant_op1_not_undef_lane(i64 %x) {
 define <2 x i64> @urem_constant_op0(i64 %x) {
 ; CHECK-LABEL: @urem_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = urem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> undef, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = urem <2 x i64> <i64 5, i64 undef>, %ins
   ret <2 x i64> %bo
 }
@@ -316,10 +316,10 @@ define <2 x i64> @urem_constant_op0(i64 %x) {
 define <2 x i64> @urem_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @urem_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = urem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> undef, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = urem <2 x i64> <i64 5, i64 2>, %ins
   ret <2 x i64> %bo
 }
@@ -327,11 +327,11 @@ define <2 x i64> @urem_constant_op0_not_undef_lane(i64 %x) {
 define <2 x i64> @urem_constant_op1(i64 %x) {
 ; CHECK-LABEL: @urem_constant_op1(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = urem i64 [[X:%.*]], 2
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 poison, i64 0>, i64 [[BO_SCALAR]], i64 1
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 1
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 1
-  %bo = urem <2 x i64> %ins, <i64 undef, i64 2>
+  %bo = urem <2 x i64> %ins, <i64 2, i64 2>
   ret <2 x i64> %bo
 }
 
@@ -349,10 +349,10 @@ define <2 x i64> @urem_constant_op1_not_undef_lane(i64 %x) {
 define <2 x i64> @srem_constant_op0(i64 %x) {
 ; CHECK-LABEL: @srem_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = srem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> undef, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = srem <2 x i64> <i64 5, i64 undef>, %ins
   ret <2 x i64> %bo
 }
@@ -360,10 +360,10 @@ define <2 x i64> @srem_constant_op0(i64 %x) {
 define <2 x i64> @srem_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @srem_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = srem i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> undef, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = srem <2 x i64> <i64 5, i64 2>, %ins
   ret <2 x i64> %bo
 }
@@ -371,11 +371,11 @@ define <2 x i64> @srem_constant_op0_not_undef_lane(i64 %x) {
 define <2 x i64> @srem_constant_op1(i64 %x) {
 ; CHECK-LABEL: @srem_constant_op1(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = srem i64 [[X:%.*]], 2
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 poison, i64 0>, i64 [[BO_SCALAR]], i64 1
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 1
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 1
-  %bo = srem <2 x i64> %ins, <i64 undef, i64 2>
+  %bo = srem <2 x i64> %ins, <i64 2, i64 2>
   ret <2 x i64> %bo
 }
 
@@ -393,10 +393,10 @@ define <2 x i64> @srem_constant_op1_not_undef_lane(i64 %x) {
 define <2 x i64> @udiv_constant_op0(i64 %x) {
 ; CHECK-LABEL: @udiv_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = udiv exact i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 5, i64 undef>, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> undef, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = udiv exact <2 x i64> <i64 5, i64 undef>, %ins
   ret <2 x i64> %bo
 }
@@ -404,10 +404,10 @@ define <2 x i64> @udiv_constant_op0(i64 %x) {
 define <2 x i64> @udiv_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @udiv_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = udiv exact i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 5, i64 2>, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> undef, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = udiv exact <2 x i64> <i64 5, i64 2>, %ins
   ret <2 x i64> %bo
 }
@@ -415,11 +415,11 @@ define <2 x i64> @udiv_constant_op0_not_undef_lane(i64 %x) {
 define <2 x i64> @udiv_constant_op1(i64 %x) {
 ; CHECK-LABEL: @udiv_constant_op1(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = udiv i64 [[X:%.*]], 2
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 poison, i64 0>, i64 [[BO_SCALAR]], i64 1
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 1
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 1
-  %bo = udiv <2 x i64> %ins, <i64 undef, i64 2>
+  %bo = udiv <2 x i64> %ins, <i64 2, i64 2>
   ret <2 x i64> %bo
 }
 
@@ -437,10 +437,10 @@ define <2 x i64> @udiv_constant_op1_not_undef_lane(i64 %x) {
 define <2 x i64> @sdiv_constant_op0(i64 %x) {
 ; CHECK-LABEL: @sdiv_constant_op0(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = sdiv i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 5, i64 undef>, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> undef, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = sdiv <2 x i64> <i64 5, i64 undef>, %ins
   ret <2 x i64> %bo
 }
@@ -448,10 +448,10 @@ define <2 x i64> @sdiv_constant_op0(i64 %x) {
 define <2 x i64> @sdiv_constant_op0_not_undef_lane(i64 %x) {
 ; CHECK-LABEL: @sdiv_constant_op0_not_undef_lane(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = sdiv i64 5, [[X:%.*]]
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> poison, i64 [[BO_SCALAR]], i64 0
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 5, i64 2>, i64 [[BO_SCALAR]], i64 0
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
-  %ins = insertelement <2 x i64> undef, i64 %x, i32 0
+  %ins = insertelement <2 x i64> splat (i64 1), i64 %x, i32 0
   %bo = sdiv <2 x i64> <i64 5, i64 2>, %ins
   ret <2 x i64> %bo
 }
@@ -459,11 +459,11 @@ define <2 x i64> @sdiv_constant_op0_not_undef_lane(i64 %x) {
 define <2 x i64> @sdiv_constant_op1(i64 %x) {
 ; CHECK-LABEL: @sdiv_constant_op1(
 ; CHECK-NEXT:    [[BO_SCALAR:%.*]] = sdiv exact i64 [[X:%.*]], 2
-; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> <i64 poison, i64 0>, i64 [[BO_SCALAR]], i64 1
+; CHECK-NEXT:    [[BO:%.*]] = insertelement <2 x i64> zeroinitializer, i64 [[BO_SCALAR]], i64 1
 ; CHECK-NEXT:    ret <2 x i64> [[BO]]
 ;
   %ins = insertelement <2 x i64> undef, i64 %x, i32 1
-  %bo = sdiv exact <2 x i64> %ins, <i64 undef, i64 2>
+  %bo = sdiv exact <2 x i64> %ins, <i64 2, i64 2>
   ret <2 x i64> %bo
 }
 
diff --git a/llvm/test/Transforms/VectorCombine/binop-scalarize.ll b/llvm/test/Transforms/VectorCombine/binop-scalarize.ll
new file mode 100644
index 0000000000000..52a706a0b59a7
--- /dev/null
+++ b/llvm/test/Transforms/VectorCombine/binop-scalarize.ll
@@ -0,0 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -S -p vector-combine | FileCheck %s
+
+; FIXME: The way we scalarize this today is by creating a
+;
+; %v = udiv <4 x i8> splat (i8 1), <i8 0, i8 1, i8 1, i8 1>
+;
+; to insert the scalar into, which is immediate UB.  Coincidentally, at creation
+; this gets constant folded into <i8 poison, i8 1, i8 1, i8 1>, but we shouldn't
+; rely on this.
+define <4 x i8> @udiv_ub(i8 %x, i8 %y) {
+; CHECK-LABEL: define <4 x i8> @udiv_ub(
+; CHECK-SAME: i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[V_SCALAR:%.*]] = udiv i8 [[X]], [[Y]]
+; CHECK-NEXT:    [[V:%.*]] = insertelement <4 x i8> <i8 poison, i8 1, i8 1, i8 1>, i8 [[V_SCALAR]], i64 0
+; CHECK-NEXT:    ret <4 x i8> [[V]]
+;
+  %x.insert = insertelement <4 x i8> splat (i8 1), i8 %x, i32 0
+  %y.insert = insertelement <4 x i8> <i8 0, i8 1, i8 1, i8 1>, i8 %y, i32 0
+  %v = udiv <4 x i8> %x.insert, %y.insert
+  ret <4 x i8> %v
+}

github-actions · 2025-05-03T12:48:15Z

⚠️ undef deprecator found issues in your code. ⚠️

You can test this locally with the following command:

git diff -U0 --pickaxe-regex -S '([^a-zA-Z0-9#_-]undef[^a-zA-Z0-9_-]|UndefValue::get)' 'HEAD~1' HEAD llvm/test/Transforms/VectorCombine/binop-scalarize.ll llvm/test/Transforms/VectorCombine/AArch64/scalarize-scalable.ll llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant-inseltpoison.ll llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll

The following files introduce new uses of undef:

llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant-inseltpoison.ll
llvm/test/Transforms/VectorCombine/X86/insert-binop-with-constant.ll

Undef is now deprecated and should only be used in the rare cases where no replacement is possible. For example, a load of uninitialized memory yields undef. You should use poison values for placeholders instead.

In tests, avoid using undef and having tests that trigger undefined behavior. If you need an operand with some unimportant value, you can add a new argument to the function and use that instead.

For example, this is considered a bad practice:

define void @fn() {
  ...
  br i1 undef, ...
}

Please use the following instead:

define void @fn(i1 %cond) {
  ...
  br i1 %cond, ...
}

Please refer to the Undefined Behavior Manual for more information.

dtcxzyw

LGTM. Thank you!

RKSimon

LGTM - cheers

…ting tests. NFC (llvm#138395) This adds a test that exercises the part of scalarizeBinOpOrCmp that produces immediate UB as described in llvm#138095 (comment), but is fortunately currently folded into a correct transform. I also noticed a bunch of immediate UB in some of the existing tests so this also cleans them up. They should still all be scalarized though.

[VectorCombine] Add tests for UB issue, remove immediate UB from exis…

6705e51

…ting tests. NFC

lukel97 requested review from RKSimon and dtcxzyw May 3, 2025 12:45

llvmbot added the llvm:transforms label May 3, 2025

lukel97 mentioned this pull request May 3, 2025

[VectorCombine] Scalarize binop-like intrinsics #138095

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dtcxzyw approved these changes May 3, 2025

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RKSimon approved these changes May 4, 2025

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lukel97 merged commit 9a7e307 into llvm:main May 5, 2025
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[VectorCombine] Add tests for UB issue, remove immediate UB from existing tests. NFC #138395

[VectorCombine] Add tests for UB issue, remove immediate UB from existing tests. NFC #138395

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lukel97 commented May 3, 2025 •

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[VectorCombine] Add tests for UB issue, remove immediate UB from existing tests. NFC #138395

[VectorCombine] Add tests for UB issue, remove immediate UB from existing tests. NFC #138395

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lukel97 commented May 3, 2025 •

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