[llvm] [InferAlignment] Increase alignment in masked load / store instrinsics if known (PR #156057)
Joseph Huber via llvm-commits
llvm-commits at lists.llvm.org
Sat Aug 30 14:05:07 PDT 2025
https://github.com/jhuber6 updated https://github.com/llvm/llvm-project/pull/156057
>From 13c384c26176f0ca935e0a78224551f91835087b Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Fri, 29 Aug 2025 11:32:52 -0500
Subject: [PATCH 1/2] [InferAlignment] Increase alignment in masked load /
store instrinsics if known
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.
---
llvm/lib/Transforms/Scalar/InferAlignment.cpp | 37 ++++++++++++++++++-
llvm/test/Transforms/InferAlignment/masked.ll | 34 +++++++++++++++++
2 files changed, 69 insertions(+), 2 deletions(-)
create mode 100644 llvm/test/Transforms/InferAlignment/masked.ll
diff --git a/llvm/lib/Transforms/Scalar/InferAlignment.cpp b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
index e9bf59c6850a3..e7d4db401aa51 100644
--- a/llvm/lib/Transforms/Scalar/InferAlignment.cpp
+++ b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
@@ -14,7 +14,9 @@
#include "llvm/Transforms/Scalar/InferAlignment.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/IRBuilder.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 +37,39 @@ 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);
+
+ Align OldAlign = cast<ConstantInt>(AlignOp)->getAlignValue();
+ Align PrefAlign = getKnownAlignment(PtrOp, DL, II);
+ Align NewAlign = Fn(PtrOp, OldAlign, PrefAlign);
+ if (NewAlign <= OldAlign)
+ return false;
+
+ Value *V = llvm::ConstantInt::get(llvm::Type::getInt32Ty(II->getContext()),
+ NewAlign.value());
+ if (II->getIntrinsicID() == Intrinsic::masked_load)
+ II->setOperand(1, V);
+ else
+ II->setOperand(2, 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>)
>From a74177b6d3cc2457faae87cbef16059ea58ea415 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Sat, 30 Aug 2025 16:04:54 -0500
Subject: [PATCH 2/2] comments
---
llvm/lib/Transforms/Scalar/InferAlignment.cpp | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/InferAlignment.cpp b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
index e7d4db401aa51..9cdcfbc7cc788 100644
--- a/llvm/lib/Transforms/Scalar/InferAlignment.cpp
+++ b/llvm/lib/Transforms/Scalar/InferAlignment.cpp
@@ -14,7 +14,6 @@
#include "llvm/Transforms/Scalar/InferAlignment.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ValueTracking.h"
-#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/KnownBits.h"
@@ -52,15 +51,18 @@ static bool tryToImproveAlign(
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 = getKnownAlignment(PtrOp, DL, II);
+ Align PrefAlign = DL.getPrefTypeAlign(Type);
Align NewAlign = Fn(PtrOp, OldAlign, PrefAlign);
if (NewAlign <= OldAlign)
return false;
- Value *V = llvm::ConstantInt::get(llvm::Type::getInt32Ty(II->getContext()),
- NewAlign.value());
+ Value *V =
+ ConstantInt::get(Type::getInt32Ty(II->getContext()), NewAlign.value());
if (II->getIntrinsicID() == Intrinsic::masked_load)
II->setOperand(1, V);
else
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