[llvm] ba818c4 - [DAG] replaceStoreOfInsertLoad - don't fold if the inserted element is implicitly truncated

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2023-08-21T11:22:07+01:00
New Revision: ba818c4019c550e1a413e1563a05b241b508defd

URL: https://github.com/llvm/llvm-project/commit/ba818c4019c550e1a413e1563a05b241b508defd
DIFF: https://github.com/llvm/llvm-project/commit/ba818c4019c550e1a413e1563a05b241b508defd.diff

LOG: [DAG] replaceStoreOfInsertLoad - don't fold if the inserted element is implicitly truncated

D152276 wasn't handling the case where the inserted element is implicitly truncated into the vector - resulting in a i1 element (implicitly truncated from i8) overwriting 8 bits instead of 1 bit.

This patch is intended to be merged into 17.x so I've just disallowed any vector element vs inserted element type mismatch - technically we could be more elegant and permit truncated stores (as long as the store is still byte sized), but the use cases for that are so limited I'd prefer to play it safe for now.

Candidate patch for #64655 17.x merge

Differential Revision: https://reviews.llvm.org/D158366

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    llvm/test/CodeGen/X86/pr64655.ll

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index bf194cb89a0bc7..2203059c711ab3 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -20508,9 +20508,11 @@ SDValue DAGCombiner::replaceStoreOfInsertLoad(StoreSDNode *ST) {
   SDValue Elt = Value.getOperand(1);
   SDValue Idx = Value.getOperand(2);
 
-  // If the element isn't byte sized then we can't compute an offset
+  // If the element isn't byte sized or is implicitly truncated then we can't
+  // compute an offset.
   EVT EltVT = Elt.getValueType();
-  if (!EltVT.isByteSized())
+  if (!EltVT.isByteSized() ||
+      EltVT != Value.getOperand(0).getValueType().getVectorElementType())
     return SDValue();
 
   auto *Ld = dyn_cast<LoadSDNode>(Value.getOperand(0));

diff  --git a/llvm/test/CodeGen/X86/pr64655.ll b/llvm/test/CodeGen/X86/pr64655.ll
index cd5775a61c23e0..f2929527c88f2e 100644
--- a/llvm/test/CodeGen/X86/pr64655.ll
+++ b/llvm/test/CodeGen/X86/pr64655.ll
@@ -41,7 +41,16 @@ define void @f(ptr %0) {
 ;
 ; AVX512-LABEL: f:
 ; AVX512:       # %bb.0:
-; AVX512-NEXT:    movb $1, 1(%rdi)
+; AVX512-NEXT:    kmovb (%rdi), %k0
+; AVX512-NEXT:    movb $-3, %al
+; AVX512-NEXT:    kmovd %eax, %k1
+; AVX512-NEXT:    kandb %k1, %k0, %k0
+; AVX512-NEXT:    movb $1, %al
+; AVX512-NEXT:    kmovd %eax, %k1
+; AVX512-NEXT:    kshiftlb $7, %k1, %k1
+; AVX512-NEXT:    kshiftrb $6, %k1, %k1
+; AVX512-NEXT:    korb %k1, %k0, %k0
+; AVX512-NEXT:    kmovb %k0, (%rdi)
 ; AVX512-NEXT:    retq
   %2 = load <8 x i1>, ptr %0
   %3 = insertelement <8 x i1> %2, i1 true, i32 1