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InstCombine: When comparing two GEPs that were derived from the same base pointer but use different types, expand the offset calculation and to the compare on the offset if profitable.

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This came up in SmallVector code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150962 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2012-02-20 15:07:47 +00:00
parent d2348639e6
commit 9bb40853ee
2 changed files with 40 additions and 0 deletions
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14
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -607,6 +607,20 @@ Instruction *InstCombiner::FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
return new ICmpInst(ICmpInst::getSignedPredicate(Cond),
GEPLHS->getOperand(0), GEPRHS->getOperand(0));
// If we're comparing GEPs with two base pointers that only differ in type
// and both GEPs have only constant indices or just one use, then fold
// the compare with the adjusted indices.
if (TD &&
(GEPLHS->hasAllConstantIndices() || GEPLHS->hasOneUse()) &&
(GEPRHS->hasAllConstantIndices() || GEPRHS->hasOneUse()) &&
PtrBase->stripPointerCasts() ==
GEPRHS->getOperand(0)->stripPointerCasts()) {
Value *Cmp = Builder->CreateICmp(ICmpInst::getSignedPredicate(Cond),
EmitGEPOffset(GEPLHS),
EmitGEPOffset(GEPRHS));
return ReplaceInstUsesWith(I, Cmp);
}
// Otherwise, the base pointers are different and the indices are
// different, bail out.
return 0;

26
test/Transforms/InstCombine/icmp.ll
View File

@ -589,3 +589,29 @@ define void @test58() nounwind {
ret void
}
declare i32 @test58_d(i64)
define i1 @test59(i8* %foo) {
%bit = bitcast i8* %foo to i32*
%gep1 = getelementptr inbounds i32* %bit, i64 2
%gep2 = getelementptr inbounds i8* %foo, i64 10
%cast1 = bitcast i32* %gep1 to i8*
%cmp = icmp ult i8* %cast1, %gep2
%use = ptrtoint i8* %cast1 to i64
%call = call i32 @test58_d(i64 %use) nounwind
ret i1 %cmp
; CHECK: @test59
; CHECK: ret i1 true
}
define i1 @test60(i8* %foo, i64 %i, i64 %j) {
%bit = bitcast i8* %foo to i32*
%gep1 = getelementptr inbounds i32* %bit, i64 %i
%gep2 = getelementptr inbounds i8* %foo, i64 %j
%cast1 = bitcast i32* %gep1 to i8*
%cmp = icmp ult i8* %cast1, %gep2
ret i1 %cmp
; CHECK: @test60
; CHECK-NEXT: %gep1.idx = shl nuw i64 %i, 2
; CHECK-NEXT: icmp slt i64 %gep1.idx, %j
; CHECK-NEXT: ret i1
}