[llvm-branch-commits] [llvm] b4bb394 - [DAG] replaceStoreOfInsertLoad - don't fold if the inserted element is implicitly truncated

[Tobias Hieta via llvm-branch-commits]

Author: Simon Pilgrim
Date: 2023-08-22T07:49:44+02:00
New Revision: b4bb394ac4c2680a153c80a7c11b3fb1405e914f

URL: https://github.com/llvm/llvm-project/commit/b4bb394ac4c2680a153c80a7c11b3fb1405e914f
DIFF: https://github.com/llvm/llvm-project/commit/b4bb394ac4c2680a153c80a7c11b3fb1405e914f.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

(cherry picked from commit ba818c4019c550e1a413e1563a05b241b508defd)

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index de909cc1079565..235f0da86b9086 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -20492,9 +20492,11 @@ 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