[llvm-branch-commits] [llvm] release/18x:[X86] Fix typo: QWORD alignment is greater than or equal to 8, not greater than 8 (#87819) (PR #88394)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: AtariDreams (AtariDreams)

<details>
<summary>Changes</summary>

Align(8) is QWORD aligned, but this was checking to see if alignment was greater than that, when it should have been checking for being greater than OR EQUAL to Align(8).

This bug was introduced in
https://github.com/llvm/llvm-project/commit/6a6af30d433d7 during the transition to the Align type.

(cherry picked from commit 8389b3bf60ef3fbd04c6efc5ff4d4605d10e7fc5)

---
Full diff: https://github.com/llvm/llvm-project/pull/88394.diff


2 Files Affected:

- (modified) llvm/lib/Target/X86/X86SelectionDAGInfo.cpp (+2-2) 
- (modified) llvm/test/CodeGen/X86/memset-minsize.ll (+13) 


``````````diff
diff --git a/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp b/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
index 7c630a2b0da080..0bff1884933d86 100644
--- a/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
+++ b/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
@@ -80,13 +80,13 @@ SDValue X86SelectionDAGInfo::EmitTargetCodeForMemset(
     uint64_t Val = ValC->getZExtValue() & 255;
 
     // If the value is a constant, then we can potentially use larger sets.
-    if (Alignment > Align(2)) {
+    if (Alignment >= Align(4)) {
       // DWORD aligned
       AVT = MVT::i32;
       ValReg = X86::EAX;
       Val = (Val << 8)  | Val;
       Val = (Val << 16) | Val;
-      if (Subtarget.is64Bit() && Alignment > Align(8)) { // QWORD aligned
+      if (Subtarget.is64Bit() && Alignment >= Align(8)) { // QWORD aligned
         AVT = MVT::i64;
         ValReg = X86::RAX;
         Val = (Val << 32) | Val;
diff --git a/llvm/test/CodeGen/X86/memset-minsize.ll b/llvm/test/CodeGen/X86/memset-minsize.ll
index 76d2928db3a9e9..cc0f2156262bba 100644
--- a/llvm/test/CodeGen/X86/memset-minsize.ll
+++ b/llvm/test/CodeGen/X86/memset-minsize.ll
@@ -136,4 +136,17 @@ entry:
   ret void
 }
 
+define void @small_memset_to_rep_stos_64(ptr %ptr) minsize nounwind {
+; CHECK-LABEL: small_memset_to_rep_stos_64:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq $16
+; CHECK-NEXT:    popq %rcx
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    rep;stosq %rax, %es:(%rdi)
+; CHECK-NEXT:    retq
+entry:
+  call void @llvm.memset.p0.i64(ptr align 8 %ptr, i8 0, i64 128, i1 false)
+  ret void
+}
+
 declare void @llvm.memset.p0.i32(ptr nocapture writeonly, i8, i32, i1)

``````````

</details>


https://github.com/llvm/llvm-project/pull/88394