release/20.x: [DAGCombiner] Don't ignore N2's undef elements in foldVSelectOfConstants (#129272)
#129383
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
@RKSimon What do you think about merging this PR to the release branch? |
|
@llvm/pr-subscribers-llvm-selectiondag @llvm/pr-subscribers-backend-x86 Author: None (llvmbot) ChangesBackport 2709366 Requested by: @dtcxzyw Full diff: https://github.com/llvm/llvm-project/pull/129383.diff 2 Files Affected:
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 9d04568483677..e921ced8326b1 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -12547,9 +12547,10 @@ SDValue DAGCombiner::foldVSelectOfConstants(SDNode *N) {
for (unsigned i = 0; i != Elts; ++i) {
SDValue N1Elt = N1.getOperand(i);
SDValue N2Elt = N2.getOperand(i);
- if (N1Elt.isUndef() || N2Elt.isUndef())
+ if (N1Elt.isUndef())
continue;
- if (N1Elt.getValueType() != N2Elt.getValueType()) {
+ // N2 should not contain undef values since it will be reused in the fold.
+ if (N2Elt.isUndef() || N1Elt.getValueType() != N2Elt.getValueType()) {
AllAddOne = false;
AllSubOne = false;
break;
diff --git a/llvm/test/CodeGen/X86/vselect-constants.ll b/llvm/test/CodeGen/X86/vselect-constants.ll
index 901f7e4a00eb5..34bda718db8f6 100644
--- a/llvm/test/CodeGen/X86/vselect-constants.ll
+++ b/llvm/test/CodeGen/X86/vselect-constants.ll
@@ -302,3 +302,21 @@ define i32 @wrong_min_signbits(<2 x i16> %x) {
%t1 = bitcast <2 x i16> %sel to i32
ret i32 %t1
}
+
+define i32 @pr129181() {
+; SSE-LABEL: pr129181:
+; SSE: # %bb.0: # %entry
+; SSE-NEXT: xorl %eax, %eax
+; SSE-NEXT: retq
+;
+; AVX-LABEL: pr129181:
+; AVX: # %bb.0: # %entry
+; AVX-NEXT: xorl %eax, %eax
+; AVX-NEXT: retq
+entry:
+ %x = insertelement <4 x i32> zeroinitializer, i32 0, i32 0
+ %cmp = icmp ult <4 x i32> %x, splat (i32 1)
+ %sel = select <4 x i1> %cmp, <4 x i32> zeroinitializer, <4 x i32> <i32 0, i32 0, i32 1, i32 poison>
+ %reduce = tail call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> %sel)
+ ret i32 %reduce
+}
|
github-project-automation
bot
moved this from Needs Triage
to Needs Merge
in LLVM Release Status
|
Does this need to be in 20.1.0 or could it wait until 20.1.1 ? |
|
I think it can wait, cheers. |
…ants` (llvm#129272) Since N2 will be reused in the fold, we cannot skip N2's undef elements if the corresponding element in N1 is well-defined. For example: ``` t2: v4i32 = BUILD_VECTOR Constant:i32<0>, Constant:i32<0>, Constant:i32<0>, Constant:i32<0> t24: v4i32 = BUILD_VECTOR undef:i32, undef:i32, Constant:i32<1>, undef:i32 t11: v4i32 = vselect t8, t2, t10 ``` Before this patch, we fold t11 into: ``` t26: v4i32 = sign_extend t8 t27: v4i32 = add t26, t24 ``` The last element of t27 is incorrect. Closes llvm#129181. (cherry picked from commit 2709366)
github-project-automation
bot
moved this from Needs Merge
to Done
in LLVM Release Status
|
@dtcxzyw (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Backport 2709366
Requested by: @dtcxzyw