[llvm] e43037b - [InferAlign] Infer alignment for memory intrinsics (#217172)

[via llvm-commits]

Author: SomeFlyingThing
Date: 2026-08-22T18:57:21+08:00
New Revision: e43037b66e8b8f97d4527620087cd1893aa189d0

URL: https://github.com/llvm/llvm-project/commit/e43037b66e8b8f97d4527620087cd1893aa189d0
DIFF: https://github.com/llvm/llvm-project/commit/e43037b66e8b8f97d4527620087cd1893aa189d0.diff

LOG: [InferAlign] Infer alignment for memory intrinsics (#217172)

Extends InferAlignment to infer and strengthen source/destination
alignment on memcpy, memmove, memset, and related memory intrinsics.

These changes were assisted by an LLM

Added: 
    llvm/test/Transforms/InferAlignment/memintrinsics.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 92f23eaccd673..9addfbd725389 100644
--- a/llvm/lib/Transforms/Scalar/InferAlignment.cpp
+++ b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
@@ -69,29 +69,27 @@ static bool tryToImproveAlign(
   if (!II)
     return false;
 
-  // TODO: Handle more memory intrinsics.
-  switch (II->getIntrinsicID()) {
-  case Intrinsic::masked_load:
-  case Intrinsic::masked_store: {
-    unsigned PtrOpIdx = II->getIntrinsicID() == Intrinsic::masked_load ? 0 : 1;
-    Value *PtrOp = II->getArgOperand(PtrOpIdx);
-    Type *Type = II->getIntrinsicID() == Intrinsic::masked_load
-                     ? II->getType()
-                     : II->getArgOperand(0)->getType();
-
-    Align OldAlign = II->getParamAlign(PtrOpIdx).valueOrOne();
-    Align PrefAlign = DL.getPrefTypeAlign(Type);
-    Align NewAlign = Fn(PtrOp, OldAlign, PrefAlign);
+  if (!isa<MemIntrinsic>(II) &&
+      II->getIntrinsicID() != Intrinsic::masked_load &&
+      II->getIntrinsicID() != Intrinsic::masked_store)
+    return false;
+
+  bool Changed = false;
+  for (unsigned ArgNo = 0; ArgNo != II->arg_size(); ++ArgNo) {
+    Value *Arg = II->getArgOperand(ArgNo);
+    if (!Arg->getType()->isPointerTy())
+      continue;
+
+    Align OldAlign = II->getParamAlign(ArgNo).valueOrOne();
+    Align NewAlign = Fn(Arg, OldAlign, Align(1));
     if (NewAlign <= OldAlign)
-      return false;
+      continue;
 
-    II->addParamAttr(PtrOpIdx,
+    II->addParamAttr(ArgNo,
                      Attribute::getWithAlignment(II->getContext(), NewAlign));
-    return true;
-  }
-  default:
-    return false;
+    Changed = true;
   }
+  return Changed;
 }
 
 using ScopedHT =

diff  --git a/llvm/test/Transforms/InferAlignment/memintrinsics.ll b/llvm/test/Transforms/InferAlignment/memintrinsics.ll
new file mode 100644
index 0000000000000..ec9817a698078
--- /dev/null
+++ b/llvm/test/Transforms/InferAlignment/memintrinsics.ll
@@ -0,0 +1,46 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt < %s -passes=infer-alignment -S | FileCheck %s
+
+declare void @llvm.memcpy.p0.p0.i64(ptr nocapture, ptr nocapture, i64, i1)
+declare void @llvm.memmove.p0.p0.i64(ptr nocapture, ptr nocapture, i64, i1)
+declare void @llvm.memset.p0.i64(ptr nocapture, i8, i64, i1)
+
+define void @memcpy(i64 %len) {
+; CHECK-LABEL: define void @memcpy(
+; CHECK-SAME: i64 [[LEN:%.*]]) {
+; CHECK-NEXT:    [[DST:%.*]] = alloca [64 x i8], align 32
+; CHECK-NEXT:    [[SRC:%.*]] = alloca [64 x i8], align 16
+; CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i64(ptr align 32 [[DST]], ptr align 16 [[SRC]], i64 [[LEN]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  %dst = alloca [64 x i8], align 32
+  %src = alloca [64 x i8], align 16
+  call void @llvm.memcpy.p0.p0.i64(ptr %dst, ptr %src, i64 %len, i1 false)
+  ret void
+}
+
+define void @memmove(i64 %len) {
+; CHECK-LABEL: define void @memmove(
+; CHECK-SAME: i64 [[LEN:%.*]]) {
+; CHECK-NEXT:    [[DST:%.*]] = alloca [64 x i8], align 64
+; CHECK-NEXT:    [[SRC:%.*]] = alloca [64 x i8], align 8
+; CHECK-NEXT:    call void @llvm.memmove.p0.p0.i64(ptr align 64 [[DST]], ptr align 8 [[SRC]], i64 [[LEN]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  %dst = alloca [64 x i8], align 64
+  %src = alloca [64 x i8], align 8
+  call void @llvm.memmove.p0.p0.i64(ptr %dst, ptr %src, i64 %len, i1 false)
+  ret void
+}
+
+define void @memset(i64 %len) {
+; CHECK-LABEL: define void @memset(
+; CHECK-SAME: i64 [[LEN:%.*]]) {
+; CHECK-NEXT:    [[DST:%.*]] = alloca [64 x i8], align 32
+; CHECK-NEXT:    call void @llvm.memset.p0.i64(ptr align 32 [[DST]], i8 0, i64 [[LEN]], i1 false)
+; CHECK-NEXT:    ret void
+;
+  %dst = alloca [64 x i8], align 32
+  call void @llvm.memset.p0.i64(ptr %dst, i8 0, i64 %len, i1 false)
+  ret void
+}