https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/129383
Backport 2709366f75b054e2cba4f61310de5a9605f4aa24 Requested by: @dtcxzyw >From e7b661513407984df3e2e8e149ddfe13bc11d063 Mon Sep 17 00:00:00 2001 From: Yingwei Zheng <dtcxzyw2...@gmail.com> Date: Sat, 1 Mar 2025 20:21:28 +0800 Subject: [PATCH] [DAGCombiner] Don't ignore N2's undef elements in `foldVSelectOfConstants` (#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 https://github.com/llvm/llvm-project/issues/129181. (cherry picked from commit 2709366f75b054e2cba4f61310de5a9605f4aa24) --- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 5 +++-- llvm/test/CodeGen/X86/vselect-constants.ll | 18 ++++++++++++++++++ 2 files changed, 21 insertions(+), 2 deletions(-) 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 +} _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
