[llvm] abda8be - [InferAlignment] Increase alignment in masked load / store instrinsics if known (#156057)

[via llvm-commits]

Author: Joseph Huber
Date: 2025-09-02T06:10:50-05:00
New Revision: abda8bed95dc3e8d3928288ac9b1e669b406cfe5

URL: https://github.com/llvm/llvm-project/commit/abda8bed95dc3e8d3928288ac9b1e669b406cfe5
DIFF: https://github.com/llvm/llvm-project/commit/abda8bed95dc3e8d3928288ac9b1e669b406cfe5.diff

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

Summary:
The masked load / store LLVM intrinsics take an argument for the
alignment. If the user is pessimistic about alignment they can provide a
value of `1` for an unaligned load. This patch updates infer-alignment
to
increase the alignment value of the alignment argument if it is known
greater than the provided one.

Ignoring the gather / scatter versions for now since they contain many
pointers.

Added: 
    llvm/test/Transforms/InferAlignment/masked.ll

Modified: 
    llvm/lib/Transforms/Scalar/InferAlignment.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/InferAlignment.cpp b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
index e9bf59c6850a3..b60b15b6c3a2b 100644
--- a/llvm/lib/Transforms/Scalar/InferAlignment.cpp
+++ b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Local.h"
@@ -35,8 +36,38 @@ 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: {
+    int AlignOpIdx = II->getIntrinsicID() == Intrinsic::masked_load ? 1 : 2;
+    Value *PtrOp = II->getIntrinsicID() == Intrinsic::masked_load
+                       ? II->getArgOperand(0)
+                       : II->getArgOperand(1);
+    Type *Type = II->getIntrinsicID() == Intrinsic::masked_load
+                     ? II->getType()
+                     : II->getArgOperand(0)->getType();
+
+    Align OldAlign =
+        cast<ConstantInt>(II->getArgOperand(AlignOpIdx))->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());
+    II->setOperand(AlignOpIdx, V);
+    return true;
+  }
+  default:
+    return false;
+  }
 }
 
 bool inferAlignment(Function &F, AssumptionCache &AC, DominatorTree &DT) {

diff  --git a/llvm/test/Transforms/InferAlignment/masked.ll b/llvm/test/Transforms/InferAlignment/masked.ll
new file mode 100644
index 0000000000000..1b8d26417d75e
--- /dev/null
+++ b/llvm/test/Transforms/InferAlignment/masked.ll
@@ -0,0 +1,34 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=infer-alignment -S | FileCheck %s
+
+define <2 x i32> @load(<2 x i1> %mask, ptr %ptr) {
+; CHECK-LABEL: define <2 x i32> @load(
+; CHECK-SAME: <2 x i1> [[MASK:%.*]], ptr [[PTR:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(ptr [[PTR]], i64 64) ]
+; CHECK-NEXT:    [[MASKED_LOAD:%.*]] = call <2 x i32> @llvm.masked.load.v2i32.p0(ptr [[PTR]], i32 64, <2 x i1> [[MASK]], <2 x i32> poison)
+; CHECK-NEXT:    ret <2 x i32> [[MASKED_LOAD]]
+;
+entry:
+  call void @llvm.assume(i1 true) [ "align"(ptr %ptr, i64 64) ]
+  %masked_load = call <2 x i32> @llvm.masked.load.v2i32.p0(ptr %ptr, i32 1, <2 x i1> %mask, <2 x i32> poison)
+  ret <2 x i32> %masked_load
+}
+
+define void @store(<2 x i1> %mask, <2 x i32> %val, ptr %ptr) {
+; CHECK-LABEL: define void @store(
+; CHECK-SAME: <2 x i1> [[MASK:%.*]], <2 x i32> [[VAL:%.*]], ptr [[PTR:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(ptr [[PTR]], i64 64) ]
+; CHECK-NEXT:    tail call void @llvm.masked.store.v2i32.p0(<2 x i32> [[VAL]], ptr [[PTR]], i32 64, <2 x i1> [[MASK]])
+; CHECK-NEXT:    ret void
+;
+entry:
+  call void @llvm.assume(i1 true) [ "align"(ptr %ptr, i64 64) ]
+  tail call void @llvm.masked.store.v2i32.p0(<2 x i32> %val, ptr %ptr, i32 1, <2 x i1> %mask)
+  ret void
+}
+
+declare void @llvm.assume(i1)
+declare <2 x i32> @llvm.masked.load.v2i32.p0(ptr, i32, <2 x i1>, <2 x i32>)
+declare void @llvm.masked.store.v2i32.p0(<2 x i32>, ptr, i32, <2 x i1>)