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[InstCombine] Fold align assume into load's !align metadata if possible. #123247

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[InstCombine] Fold align assume into load's !align metadata if possible. #123247

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789dc63
[InstCombine] Add test for removing redundant assume if align matches.
fhahn Oct 7, 2025
c64ad8f
[InstCombine] Fold align assume into load's !align metadata if possible.
fhahn Oct 2, 2025
b0f7aaa
[EarlyCSE] Rematerialize alignment assumption.
fhahn Sep 18, 2024
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15 changes: 12 additions & 3 deletions llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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Expand Up @@ -3446,9 +3446,18 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
KnownBits Known = computeKnownBits(RK.WasOn, /*CtxI=*/nullptr);
unsigned TZ = std::min(Known.countMinTrailingZeros(),
Value::MaxAlignmentExponent);
if ((1ULL << TZ) < RK.ArgValue)
continue;
return CallBase::removeOperandBundle(II, OBU.getTagID());
if ((1ULL << TZ) >= RK.ArgValue)
return CallBase::removeOperandBundle(II, OBU.getTagID());

auto *LI = dyn_cast<LoadInst>(OBU.Inputs[0]);
if (LI &&
isValidAssumeForContext(II, LI, &DT, /*AllowEphemerals=*/true)) {
LI->setMetadata(LLVMContext::MD_align,
MDNode::get(II->getContext(),
ValueAsMetadata::getConstant(
Builder.getInt64(RK.ArgValue))));
return CallBase::removeOperandBundle(II, OBU.getTagID());
}
}
}

Expand Down
9 changes: 9 additions & 0 deletions llvm/lib/Transforms/Scalar/EarlyCSE.cpp
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Expand Up @@ -31,6 +31,7 @@
#include "llvm/IR/Constants.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
Expand Down Expand Up @@ -1600,6 +1601,14 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
if (InVal.IsLoad)
if (auto *I = dyn_cast<Instruction>(Op))
combineMetadataForCSE(I, &Inst, false);
if (auto *AlignMD = Inst.getMetadata(LLVMContext::MD_align)) {
auto *A = mdconst::extract<ConstantInt>(AlignMD->getOperand(0));
if (Op->getPointerAlignment(SQ.DL).value() % A->getZExtValue() != 0) {
IRBuilder B(&Inst);
B.CreateAlignmentAssumption(SQ.DL, Op, A);
}
}

if (!Inst.use_empty())
Inst.replaceAllUsesWith(Op);
salvageKnowledge(&Inst, &AC);
Expand Down
30 changes: 24 additions & 6 deletions llvm/test/Transforms/InstCombine/assume-align.ll
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Expand Up @@ -123,18 +123,26 @@ define i8 @assume_align_non_pow2(ptr %p) {
ret i8 %v
}

; TODO: Can fold alignment assumption into !align metadata on load.
define ptr @fold_assume_align_pow2_of_loaded_pointer_into_align_metadata(ptr %p) {
; CHECK-LABEL: @fold_assume_align_pow2_of_loaded_pointer_into_align_metadata(
; CHECK-NEXT: [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8
; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[P2]], i64 8) ]
; CHECK-NEXT: [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8, !align [[META0:![0-9]+]]
; CHECK-NEXT: ret ptr [[P2]]
;
%p2 = load ptr, ptr %p
call void @llvm.assume(i1 true) [ "align"(ptr %p2, i64 8) ]
ret ptr %p2
}

define ptr @fold_assume_align_i32_pow2_of_loaded_pointer_into_align_metadata(ptr %p) {
; CHECK-LABEL: @fold_assume_align_i32_pow2_of_loaded_pointer_into_align_metadata(
; CHECK-NEXT: [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8, !align [[META0]]
; CHECK-NEXT: ret ptr [[P2]]
;
%p2 = load ptr, ptr %p
call void @llvm.assume(i1 true) [ "align"(ptr %p2, i32 8) ]
ret ptr %p2
}

define ptr @dont_fold_assume_align_pow2_of_loaded_pointer_into_align_metadata_due_to_call(ptr %p) {
; CHECK-LABEL: @dont_fold_assume_align_pow2_of_loaded_pointer_into_align_metadata_due_to_call(
; CHECK-NEXT: [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8
Expand Down Expand Up @@ -187,7 +195,7 @@ define ptr @redundant_assume_align_1(ptr %p) {

define ptr @redundant_assume_align_8_via_align_metadata(ptr %p) {
; CHECK-LABEL: @redundant_assume_align_8_via_align_metadata(
; CHECK-NEXT: [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8, !align [[META0:![0-9]+]]
; CHECK-NEXT: [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8, !align [[META0]]
; CHECK-NEXT: call void @foo(ptr [[P2]])
; CHECK-NEXT: ret ptr [[P2]]
;
Expand All @@ -199,8 +207,7 @@ define ptr @redundant_assume_align_8_via_align_metadata(ptr %p) {

define ptr @assume_align_16_via_align_metadata(ptr %p) {
; CHECK-LABEL: @assume_align_16_via_align_metadata(
; CHECK-NEXT: [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8, !align [[META0]]
; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[P2]], i32 16) ]
; CHECK-NEXT: [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8, !align [[META1:![0-9]+]]
; CHECK-NEXT: call void @foo(ptr [[P2]])
; CHECK-NEXT: ret ptr [[P2]]
;
Expand Down Expand Up @@ -247,6 +254,16 @@ define ptr @redundant_assume_align_8_via_asume(ptr %p) {
ret ptr %p
}

@g2 = external constant i128, align 8

define void @redundant_assume_align_global_eq() {
; CHECK-LABEL: @redundant_assume_align_global_eq(
; CHECK-NEXT: ret void
;
call void @llvm.assume(i1 true) [ "align"(ptr @g2, i64 8) ]
ret void
}

define ptr @assume_align_1(ptr %p) {
; CHECK-LABEL: @assume_align_1(
; CHECK-NEXT: call void @foo(ptr [[P:%.*]])
Expand All @@ -273,4 +290,5 @@ define ptr @assume_load_pointer_result(ptr %p, i64 %align) {

;.
; CHECK: [[META0]] = !{i64 8}
; CHECK: [[META1]] = !{i64 16}
;.
16 changes: 8 additions & 8 deletions llvm/test/Transforms/PhaseOrdering/AArch64/infer-align-from-assumption.ll
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Expand Up @@ -8,8 +8,7 @@ declare void @llvm.assume(i1 noundef)
define i32 @earlycse_entry(ptr %p) {
; CHECK-LABEL: define i32 @earlycse_entry(
; CHECK-SAME: ptr captures(none) [[P:%.*]]) local_unnamed_addr {
; CHECK-NEXT: [[L_I:%.*]] = load ptr, ptr [[P]], align 8
; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[L_I]], i64 4) ]
; CHECK-NEXT: [[L_I:%.*]] = load ptr, ptr [[P]], align 8, !align [[META0:![0-9]+]]
; CHECK-NEXT: [[L_ASSUME_ALIGNED_I_I:%.*]] = load i32, ptr [[L_I]], align 4
; CHECK-NEXT: [[R_I_I:%.*]] = tail call i32 @swap(i32 [[L_ASSUME_ALIGNED_I_I]])
; CHECK-NEXT: [[L_2_I:%.*]] = load ptr, ptr [[P]], align 8
Expand All @@ -31,8 +30,7 @@ define i32 @earlycse_entry(ptr %p) {
define i32 @earlycse_fn1(ptr %p) {
; CHECK-LABEL: define i32 @earlycse_fn1(
; CHECK-SAME: ptr captures(none) [[P:%.*]]) local_unnamed_addr {
; CHECK-NEXT: [[L:%.*]] = load ptr, ptr [[P]], align 8
; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[L]], i64 4) ]
; CHECK-NEXT: [[L:%.*]] = load ptr, ptr [[P]], align 8, !align [[META0]]
; CHECK-NEXT: [[L_ASSUME_ALIGNED_I:%.*]] = load i32, ptr [[L]], align 4
; CHECK-NEXT: [[R_I:%.*]] = tail call i32 @swap(i32 [[L_ASSUME_ALIGNED_I]])
; CHECK-NEXT: [[L_2:%.*]] = load ptr, ptr [[P]], align 8
Expand Down Expand Up @@ -67,8 +65,7 @@ declare i32 @swap(i32)
define void @sroa_align_entry(ptr %p) {
; CHECK-LABEL: define void @sroa_align_entry(
; CHECK-SAME: ptr readonly captures(none) [[P:%.*]]) local_unnamed_addr #[[ATTR1:[0-9]+]] {
; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[P]], i64 8) ]
; CHECK-NEXT: [[DOT0_COPYLOAD_I_I_I:%.*]] = load i64, ptr [[P]], align 8
; CHECK-NEXT: [[DOT0_COPYLOAD_I_I_I:%.*]] = load i64, ptr [[P]], align 1
; CHECK-NEXT: [[TMP2:%.*]] = inttoptr i64 [[DOT0_COPYLOAD_I_I_I]] to ptr
; CHECK-NEXT: store i32 0, ptr [[TMP2]], align 4
; CHECK-NEXT: ret void
Expand All @@ -83,8 +80,7 @@ define void @sroa_align_entry(ptr %p) {
define ptr @sroa_fn1(ptr %p) {
; CHECK-LABEL: define ptr @sroa_fn1(
; CHECK-SAME: ptr readonly captures(none) [[P:%.*]]) local_unnamed_addr #[[ATTR2:[0-9]+]] {
; CHECK-NEXT: [[L:%.*]] = load ptr, ptr [[P]], align 8
; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[L]], i64 8) ]
; CHECK-NEXT: [[L:%.*]] = load ptr, ptr [[P]], align 8, !align [[META1:![0-9]+]]
; CHECK-NEXT: [[L_FN3_I_I:%.*]] = load i64, ptr [[L]], align 8
; CHECK-NEXT: [[I_I:%.*]] = inttoptr i64 [[L_FN3_I_I]] to ptr
; CHECK-NEXT: ret ptr [[I_I]]
Expand Down Expand Up @@ -118,3 +114,7 @@ define i64 @sroa_fn3(ptr %0) {
%l.fn3 = load i64, ptr %0, align 1
ret i64 %l.fn3
}
;.
; CHECK: [[META0]] = !{i64 4}
; CHECK: [[META1]] = !{i64 8}
;.
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