[llvm] [InferAlignment] Increase alignment in masked load / store instrinsics if known (PR #156057)

[Matt Arsenault via llvm-commits]

================
@@ -35,8 +36,42 @@ static bool tryToImproveAlign(
       return true;
     }
   }
-  // TODO: Also handle memory intrinsics.
-  return false;
+
+  IntrinsicInst *II = dyn_cast<IntrinsicInst>(I);
+  if (!II)
+    return false;
+
+  // TODO: Handle more memory intrinsics.
+  switch (II->getIntrinsicID()) {
+  case Intrinsic::masked_load:
+  case Intrinsic::masked_store: {
+    Value *PtrOp = II->getIntrinsicID() == Intrinsic::masked_load
+                       ? II->getArgOperand(0)
+                       : II->getArgOperand(1);
+    Value *AlignOp = II->getIntrinsicID() == Intrinsic::masked_load
+                         ? II->getArgOperand(1)
+                         : II->getArgOperand(2);
+    Type *Type = II->getIntrinsicID() == Intrinsic::masked_load
+                     ? II->getType()
+                     : II->getArgOperand(0)->getType();
+
+    Align OldAlign = cast<ConstantInt>(AlignOp)->getAlignValue();
+    Align PrefAlign = DL.getPrefTypeAlign(Type);
+    Align NewAlign = Fn(PtrOp, OldAlign, PrefAlign);
+    if (NewAlign <= OldAlign)
+      return false;
+
+    Value *V =
+        ConstantInt::get(Type::getInt32Ty(II->getContext()), NewAlign.value());
+    if (II->getIntrinsicID() == Intrinsic::masked_load)
+      II->setOperand(1, V);
+    else
+      II->setOperand(2, V);
----------------
arsenm wrote:

```suggestion
    II->setOperand(AlignOpIdx, V);
```

https://github.com/llvm/llvm-project/pull/156057