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[InstCombine] Limit canonicalization of extractelement(cast) to constant index or same basic block. #166227

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[InstCombine] Limit canonicalization of extractelement(cast) to constant index or same basic block. #166227

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aa49b2b
[InstCombine] Limit canonicalization of extractelement(cast) to const…
azwolski Nov 3, 2025
298613c
[InstCombine] Update vec_extract_var_elt.ll test checks
azwolski Nov 3, 2025
91e0c1b
[InstCombine] Refactor canonicalization of extractelement(cast) to co…
azwolski Nov 3, 2025
742d97e
[InstCombine] Add test_poison_branch test and update vec_extract_var_…
azwolski Nov 3, 2025
4d8d8fd
[InstCombine] Remove unused declaration of @use_vi in vec_extract_var…
azwolski Nov 3, 2025
4a1267a
[InstCombine] Fix formatting in visitExtractElementInst
azwolski Nov 3, 2025
99da128
[InstCombine] Simplify conditional checks for extractelement(cast) ca…
azwolski Nov 19, 2025
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3 changes: 2 additions & 1 deletion llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -588,7 +588,8 @@ Instruction *InstCombinerImpl::visitExtractElementInst(ExtractElementInst &EI) {
// Canonicalize extractelement(cast) -> cast(extractelement).
// Bitcasts can change the number of vector elements, and they cost
// nothing.
if (CI->hasOneUse() && (CI->getOpcode() != Instruction::BitCast)) {
if (CI->hasOneUse() && (CI->getOpcode() != Instruction::BitCast) &&
(EI.getParent() == CI->getParent() || isa<ConstantInt>(Index))) {
Value *EE = Builder.CreateExtractElement(CI->getOperand(0), Index);
return CastInst::Create(CI->getOpcode(), EE, EI.getType());
}
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40 changes: 35 additions & 5 deletions llvm/test/Transforms/InstCombine/vec_extract_var_elt.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -40,19 +40,50 @@ define i32 @test_bitcast(i32 %i) {

declare void @use(i32)

define void @test_poison_branch(<4 x float> %in, i32 %a, i1 %cond) {
; CHECK-LABEL: define void @test_poison_branch(
; CHECK-SAME: <4 x float> [[IN:%.*]], i32 [[A:%.*]], i1 [[COND:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[I:%.*]] = add i32 [[A]], -2
; CHECK-NEXT: br i1 [[COND]], label %[[TRUE:.*]], label %[[FALSE:.*]]
; CHECK: [[TRUE]]:
; CHECK-NEXT: call void @use(i32 [[I]])
; CHECK-NEXT: br label %[[DONE:.*]]
; CHECK: [[FALSE]]:
; CHECK-NEXT: [[TMP0:%.*]] = extractelement <4 x float> [[IN]], i32 [[I]]
; CHECK-NEXT: [[ELEM:%.*]] = fptosi float [[TMP0]] to i32
; CHECK-NEXT: call void @use(i32 [[ELEM]])
; CHECK-NEXT: br label %[[DONE]]
; CHECK: [[DONE]]:
; CHECK-NEXT: ret void
;
entry:
%vi = fptosi <4 x float> %in to <4 x i32>
%i = add i32 %a, -2
br i1 %cond, label %true, label %false
true:
call void @use(i32 %i)
br label %done
false:
%elem = extractelement <4 x i32> %vi, i32 %i
call void @use(i32 %elem)
br label %done
done:
ret void
}

define void @test_loop(<4 x float> %in) {
; CHECK-LABEL: define void @test_loop(
; CHECK-SAME: <4 x float> [[IN:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: [[R:%.*]] = call <4 x float> @llvm.x86.sse41.round.ps(<4 x float> [[IN]], i32 9)
; CHECK-NEXT: [[VI:%.*]] = fptosi <4 x float> [[IN]] to <4 x i32>
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
; CHECK-NEXT: [[I:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[NEXT:%.*]], %[[LATCH:.*]] ]
; CHECK-NEXT: [[COND:%.*]] = icmp samesign ult i32 [[I]], 4
; CHECK-NEXT: br i1 [[COND]], label %[[BODY:.*]], label %[[DONE:.*]]
; CHECK: [[BODY]]:
; CHECK-NEXT: [[TMP0:%.*]] = extractelement <4 x float> [[R]], i32 [[I]]
; CHECK-NEXT: [[ELEM:%.*]] = fptosi float [[TMP0]] to i32
; CHECK-NEXT: [[ELEM:%.*]] = extractelement <4 x i32> [[VI]], i32 [[I]]
; CHECK-NEXT: call void @use(i32 [[ELEM]])
; CHECK-NEXT: br label %[[LATCH]]
; CHECK: [[LATCH]]:
Expand All @@ -62,8 +93,7 @@ define void @test_loop(<4 x float> %in) {
; CHECK-NEXT: ret void
;
entry:
%r = call <4 x float> @llvm.x86.sse41.round.ps(<4 x float> %in, i32 9)
%vi = fptosi <4 x float> %r to <4 x i32>
%vi = fptosi <4 x float> %in to <4 x i32>
br label %loop
loop:
%i = phi i32 [ 0, %entry ], [ %next, %latch ]
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