[llvm] ed866d9 - [X86][Combine] Ensure single use chain in extract-load combine (#136520)

[via llvm-commits]

Author: Evgenii Kudriashov
Date: 2025-04-24T16:16:50+02:00
New Revision: ed866d994c3b074cb1b7a380b1ce9169dde3362c

URL: https://github.com/llvm/llvm-project/commit/ed866d994c3b074cb1b7a380b1ce9169dde3362c
DIFF: https://github.com/llvm/llvm-project/commit/ed866d994c3b074cb1b7a380b1ce9169dde3362c.diff

LOG: [X86][Combine] Ensure single use chain in extract-load combine (#136520)

The problem is that `SrcBC = peekThroughBitcasts(Src)` doesn't ensure
single use chain. It results in the situation when a cast may have
multiple users and instead of replacing a load we introduce a new one.
The situation is worsened by the fact that we've replaced the token from
the original load and its correct memory order now is not guaranteed.

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp
    llvm/test/CodeGen/X86/extractelement-load.ll

Removed: 
    


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diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 4a9121baba7db..0fc50dc1a87b6 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -46268,7 +46268,8 @@ static SDValue combineExtractWithShuffle(SDNode *N, SelectionDAG &DAG,
 
   // If we're extracting a single element from a broadcast load and there are
   // no other users, just create a single load.
-  if (SrcBC.getOpcode() == X86ISD::VBROADCAST_LOAD && SrcBC.hasOneUse()) {
+  if (peekThroughOneUseBitcasts(Src).getOpcode() == X86ISD::VBROADCAST_LOAD &&
+      SrcBC.hasOneUse()) {
     auto *MemIntr = cast<MemIntrinsicSDNode>(SrcBC);
     unsigned SrcBCWidth = SrcBC.getScalarValueSizeInBits();
     if (MemIntr->getMemoryVT().getSizeInBits() == SrcBCWidth &&

diff  --git a/llvm/test/CodeGen/X86/extractelement-load.ll b/llvm/test/CodeGen/X86/extractelement-load.ll
index c251f2a22f83a..ce68eebd5b752 100644
--- a/llvm/test/CodeGen/X86/extractelement-load.ll
+++ b/llvm/test/CodeGen/X86/extractelement-load.ll
@@ -573,14 +573,17 @@ define dso_local <2 x float> @multiuse_of_single_value_from_vbroadcast_load(ptr
 ; X64-AVX-LABEL: multiuse_of_single_value_from_vbroadcast_load:
 ; X64-AVX:       # %bb.0:
 ; X64-AVX-NEXT:    pushq %rbx
+; X64-AVX-NEXT:    subq $16, %rsp
 ; X64-AVX-NEXT:    movq %rsi, %rbx
-; X64-AVX-NEXT:    vmovsd 32(%rsi), %xmm0 # xmm0 = mem[0],zero
-; X64-AVX-NEXT:    vmovsd %xmm0, (%rdi)
+; X64-AVX-NEXT:    vmovddup {{.*#+}} xmm0 = mem[0,0]
+; X64-AVX-NEXT:    vmovaps %xmm0, (%rsp) # 16-byte Spill
+; X64-AVX-NEXT:    vmovlps %xmm0, (%rdi)
 ; X64-AVX-NEXT:    vmovaps 32(%rsi), %xmm0
 ; X64-AVX-NEXT:    callq ccosf at PLT
 ; X64-AVX-NEXT:    vmovlps %xmm0, 32(%rbx)
-; X64-AVX-NEXT:    vmovddup 32(%rbx), %xmm0 # xmm0 = mem[0,0]
+; X64-AVX-NEXT:    vmovaps (%rsp), %xmm0 # 16-byte Reload
 ; X64-AVX-NEXT:    callq ccosf at PLT
+; X64-AVX-NEXT:    addq $16, %rsp
 ; X64-AVX-NEXT:    popq %rbx
 ; X64-AVX-NEXT:    retq
   %p1 = getelementptr [5 x <2 x float>], ptr %arr, i64 0, i64 3