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[InstCombine] Remove redundant align 1 assumptions. #160695

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Merged
merged 2 commits into from
Sep 25, 2025
Merged

[InstCombine] Remove redundant align 1 assumptions. #160695

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[InstCombine] Remove redundant align 1 assumptions.
fhahn Sep 25, 2025
f2126d5
!fixup update test
fhahn Sep 25, 2025
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4 changes: 4 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3412,6 +3412,10 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
!isPowerOf2_64(RK.ArgValue) || !isa<ConstantInt>(RK.IRArgValue))
continue;

// Remove align 1 bundles; they don't add any useful information.
if (RK.ArgValue == 1)
return CallBase::removeOperandBundle(II, OBU.getTagID());
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Side note (as this is not the only place with this problem), but this API doesn't do the right thing if there are multiple assume operand bundles with the same name. No idea whether that's supposed to be allowed or only permitted by accident.


// Don't try to remove align assumptions for pointers derived from
// arguments. We might lose information if the function gets inline and
// the align argument attribute disappears.
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3 changes: 1 addition & 2 deletions llvm/test/Transforms/InstCombine/assume-align.ll
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Expand Up @@ -249,8 +249,7 @@ define ptr @redundant_assume_align_8_via_asume(ptr %p) {

define ptr @assume_align_1(ptr %p) {
; CHECK-LABEL: @assume_align_1(
; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[P:%.*]], i32 1) ]
; CHECK-NEXT: call void @foo(ptr [[P]])
; CHECK-NEXT: call void @foo(ptr [[P:%.*]])
; CHECK-NEXT: ret ptr [[P]]
;
call void @llvm.assume(i1 true) [ "align"(ptr %p, i32 1) ]
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