[llvm] [X86] combineTruncate - drop load alignment after (trunc (srl (load p), amt)) -> (load p + amt/8) fold (PR #165436)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

<details>
<summary>Changes</summary>

The pointer adjustment no longer guarantees any alignment

Missed in #<!-- -->165266 and only noticed in some follow up work

---
Full diff: https://github.com/llvm/llvm-project/pull/165436.diff


1 Files Affected:

- (modified) llvm/lib/Target/X86/X86ISelLowering.cpp (+2-1) 


``````````diff
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index b86020aa512ea..5785440a20e43 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -54679,7 +54679,8 @@ static SDValue combineTruncate(SDNode *N, SelectionDAG &DAG,
         SDValue NewPtr = DAG.getMemBasePlusOffset(
             Ld->getBasePtr(), PtrByteOfs, DL, SDNodeFlags::NoUnsignedWrap);
         SDValue NewLoad =
-            DAG.getLoad(VT, DL, Ld->getChain(), NewPtr, Ld->getMemOperand());
+            DAG.getLoad(VT, DL, Ld->getChain(), NewPtr, Ld->getPointerInfo(),
+                        Align(), Ld->getMemOperand()->getFlags());
         DAG.ReplaceAllUsesOfValueWith(Src.getOperand(0).getValue(1),
                                       NewLoad.getValue(1));
         return NewLoad;

``````````

</details>


https://github.com/llvm/llvm-project/pull/165436