[llvm] [InferAlign] Infer alignment for memory intrinsics (PR #217172)
via llvm-commits
llvm-commits at lists.llvm.org
Fri Aug 21 13:55:40 PDT 2026
https://github.com/SomeFlyingThing updated https://github.com/llvm/llvm-project/pull/217172
>From 5256dd2d510b55fd4be3890cdd28f894d257ae3e Mon Sep 17 00:00:00 2001
From: SomeFlyingThing <306498559+SomeFlyingThing at users.noreply.github.com>
Date: Wed, 19 Aug 2026 11:56:31 +1200
Subject: [PATCH 1/2] [InferAlignment] Infer alignment for memory intrinsics
Use known-bits and base-pointer alignment information to strengthen the
source and destination alignment attributes of memory intrinsics.
This extends InferAlignment to memcpy, memmove, memset, and their inline
variants through the MemIntrinsic hierarchy.
---
llvm/lib/Transforms/Scalar/InferAlignment.cpp | 22 +++++++++++++
.../InferAlignment/memintrinsics.ll | 31 +++++++++++++++++++
2 files changed, 53 insertions(+)
create mode 100644 llvm/test/Transforms/InferAlignment/memintrinsics.ll
diff --git a/llvm/lib/Transforms/Scalar/InferAlignment.cpp b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
index 92f23eaccd673f..908d92be7c16e0 100644
--- a/llvm/lib/Transforms/Scalar/InferAlignment.cpp
+++ b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
@@ -69,6 +69,28 @@ static bool tryToImproveAlign(
if (!II)
return false;
+ if (auto *MI = dyn_cast<MemIntrinsic>(II)) {
+ bool Changed = false;
+
+ Align OldDestAlign = MI->getDestAlign().valueOrOne();
+ Align NewDestAlign = Fn(MI->getRawDest(), OldDestAlign, Align(1));
+ if (NewDestAlign > OldDestAlign) {
+ MI->setDestAlignment(NewDestAlign);
+ Changed = true;
+ }
+
+ if (auto *MTI = dyn_cast<MemTransferInst>(MI)) {
+ Align OldSourceAlign = MTI->getSourceAlign().valueOrOne();
+ Align NewSourceAlign = Fn(MTI->getRawSource(), OldSourceAlign, Align(1));
+ if (NewSourceAlign > OldSourceAlign) {
+ MTI->setSourceAlignment(NewSourceAlign);
+ Changed = true;
+ }
+ }
+
+ return Changed;
+ }
+
// TODO: Handle more memory intrinsics.
switch (II->getIntrinsicID()) {
case Intrinsic::masked_load:
diff --git a/llvm/test/Transforms/InferAlignment/memintrinsics.ll b/llvm/test/Transforms/InferAlignment/memintrinsics.ll
new file mode 100644
index 00000000000000..4354f1d4a72af9
--- /dev/null
+++ b/llvm/test/Transforms/InferAlignment/memintrinsics.ll
@@ -0,0 +1,31 @@
+; 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: call void @llvm.memcpy.p0.p0.i64(ptr align 32 %dst, ptr align 16 %src, i64 %len, i1 false)
+ %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: call void @llvm.memmove.p0.p0.i64(ptr align 64 %dst, ptr align 8 %src, i64 %len, i1 false)
+ %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: call void @llvm.memset.p0.i64(ptr align 32 %dst, i8 0, i64 %len, i1 false)
+ %dst = alloca [64 x i8], align 32
+ call void @llvm.memset.p0.i64(ptr %dst, i8 0, i64 %len, i1 false)
+ ret void
+}
>From d42f2cc523ee804336253e00f3c375cdbdf135f4 Mon Sep 17 00:00:00 2001
From: SomeFlyingThing <306498559+SomeFlyingThing at users.noreply.github.com>
Date: Sat, 22 Aug 2026 08:55:27 +1200
Subject: [PATCH 2/2] [InferAlign] Generalize intrinsic alignment inference
---
llvm/lib/Transforms/Scalar/InferAlignment.cpp | 54 ++++++-------------
.../InferAlignment/memintrinsics.ll | 21 ++++++--
2 files changed, 33 insertions(+), 42 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/InferAlignment.cpp b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
index 908d92be7c16e0..9addfbd725389c 100644
--- a/llvm/lib/Transforms/Scalar/InferAlignment.cpp
+++ b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
@@ -69,51 +69,27 @@ static bool tryToImproveAlign(
if (!II)
return false;
- if (auto *MI = dyn_cast<MemIntrinsic>(II)) {
- bool Changed = false;
-
- Align OldDestAlign = MI->getDestAlign().valueOrOne();
- Align NewDestAlign = Fn(MI->getRawDest(), OldDestAlign, Align(1));
- if (NewDestAlign > OldDestAlign) {
- MI->setDestAlignment(NewDestAlign);
- Changed = true;
- }
-
- if (auto *MTI = dyn_cast<MemTransferInst>(MI)) {
- Align OldSourceAlign = MTI->getSourceAlign().valueOrOne();
- Align NewSourceAlign = Fn(MTI->getRawSource(), OldSourceAlign, Align(1));
- if (NewSourceAlign > OldSourceAlign) {
- MTI->setSourceAlignment(NewSourceAlign);
- Changed = true;
- }
- }
+ if (!isa<MemIntrinsic>(II) &&
+ II->getIntrinsicID() != Intrinsic::masked_load &&
+ II->getIntrinsicID() != Intrinsic::masked_store)
+ return false;
- return Changed;
- }
+ bool Changed = false;
+ for (unsigned ArgNo = 0; ArgNo != II->arg_size(); ++ArgNo) {
+ Value *Arg = II->getArgOperand(ArgNo);
+ if (!Arg->getType()->isPointerTy())
+ continue;
- // 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);
+ 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
index 4354f1d4a72af9..ec9817a6980789 100644
--- a/llvm/test/Transforms/InferAlignment/memintrinsics.ll
+++ b/llvm/test/Transforms/InferAlignment/memintrinsics.ll
@@ -1,3 +1,4 @@
+; 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)
@@ -6,7 +7,12 @@ declare void @llvm.memset.p0.i64(ptr nocapture, i8, i64, i1)
define void @memcpy(i64 %len) {
; CHECK-LABEL: define void @memcpy(
-; CHECK: call void @llvm.memcpy.p0.p0.i64(ptr align 32 %dst, ptr align 16 %src, i64 %len, i1 false)
+; 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)
@@ -15,7 +21,12 @@ define void @memcpy(i64 %len) {
define void @memmove(i64 %len) {
; CHECK-LABEL: define void @memmove(
-; CHECK: call void @llvm.memmove.p0.p0.i64(ptr align 64 %dst, ptr align 8 %src, i64 %len, i1 false)
+; 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)
@@ -24,7 +35,11 @@ define void @memmove(i64 %len) {
define void @memset(i64 %len) {
; CHECK-LABEL: define void @memset(
-; CHECK: call void @llvm.memset.p0.i64(ptr align 32 %dst, i8 0, i64 %len, i1 false)
+; 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
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