[llvm] [DAGCombiner] Remove unnecessary commonAlignment from CombineExtLoad. (PR #81705)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: Craig Topper (topperc)

<details>
<summary>Changes</summary>

The getAlign function for a load returns the commonAlignment of the "base align" and the offset stored in the MachinePointerInfo.

We're splitting a load here, so we should take the base alignment from the original load without any offset that may already exist in the original load. The new load can then maintain its own alignment using just the base alignment and its own offset.

Noticed by inspection.

---
Full diff: https://github.com/llvm/llvm-project/pull/81705.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (+5-5) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 52011e593f2e0a..f35466fb607360 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -12971,12 +12971,12 @@ SDValue DAGCombiner::CombineExtLoad(SDNode *N) {
   SDValue BasePtr = LN0->getBasePtr();
   for (unsigned Idx = 0; Idx < NumSplits; Idx++) {
     const unsigned Offset = Idx * Stride;
-    const Align Align = commonAlignment(LN0->getAlign(), Offset);
 
-    SDValue SplitLoad = DAG.getExtLoad(
-        ExtType, SDLoc(LN0), SplitDstVT, LN0->getChain(), BasePtr,
-        LN0->getPointerInfo().getWithOffset(Offset), SplitSrcVT, Align,
-        LN0->getMemOperand()->getFlags(), LN0->getAAInfo());
+    SDValue SplitLoad =
+        DAG.getExtLoad(ExtType, SDLoc(LN0), SplitDstVT, LN0->getChain(),
+                       BasePtr, LN0->getPointerInfo().getWithOffset(Offset),
+                       SplitSrcVT, LN0->getOriginalAlign(),
+                       LN0->getMemOperand()->getFlags(), LN0->getAAInfo());
 
     BasePtr = DAG.getMemBasePlusOffset(BasePtr, TypeSize::getFixed(Stride), DL);
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/81705