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[InstCombine] Fold icmp eq of non-inbounds geps

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We can fold equality comparisons of non-inbounds geps to offset
comparison (https://alive2.llvm.org/ce/z/x2Zp8b). The inbounds
requirement is only necessary for relational comparisons.
This commit is contained in:
Nikita Popov 2023-03-21 10:46:13 +01:00
parent 5d17ae2d5d
commit 289542b1e7
2 changed files with 4 additions and 4 deletions
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3
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -884,7 +884,8 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
// Only lower this if the icmp is the only user of the GEP or if we expect
// the result to fold to a constant!
if (GEPsInBounds && (isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) &&
if ((GEPsInBounds || CmpInst::isEquality(Cond)) &&
(isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) &&
(isa<ConstantExpr>(GEPRHS) || GEPRHS->hasOneUse())) {
// ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2) ---> (OFFSET1 cmp OFFSET2)
Value *L = EmitGEPOffset(GEPLHS);

5
llvm/test/Transforms/InstCombine/icmp-gep.ll
View File

@ -299,9 +299,8 @@ define i1 @test_gep_ult_no_inbounds(ptr %foo, i64 %i, i64 %j) {
define i1 @test_gep_eq_no_inbounds(ptr %foo, i64 %i, i64 %j) {
; CHECK-LABEL: @test_gep_eq_no_inbounds(
; CHECK-NEXT: [[GEP1:%.*]] = getelementptr i32, ptr [[FOO:%.*]], i64 [[I:%.*]]
; CHECK-NEXT: [[GEP2:%.*]] = getelementptr i8, ptr [[FOO]], i64 [[J:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[GEP1]], [[GEP2]]
; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl i64 [[I:%.*]], 2
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[GEP1_IDX]], [[J:%.*]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr i32, ptr %foo, i64 %i