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[InstCombine] propagate 'nsw' on pointer difference of 'inbounds' geps (PR47430)

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There's no signed wrap if both geps have 'inbounds':
https://alive2.llvm.org/ce/z/nZkQTg
https://alive2.llvm.org/ce/z/7qFauh
This commit is contained in:
Sanjay Patel 2020-09-10 17:09:36 -04:00
parent 7ae9f7c717
commit f7e01a7376
3 changed files with 16 additions and 9 deletions
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7
lib/Transforms/InstCombine/InstCombineAddSub.cpp
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@ -1671,11 +1671,12 @@ Value *InstCombinerImpl::OptimizePointerDifference(Value *LHS, Value *RHS,
I->getOpcode() == Instruction::Mul)
I->setHasNoUnsignedWrap();
// If we had a constant expression GEP on the other side offsetting the
// pointer, subtract it from the offset we have.
// If we have a 2nd GEP of the same base pointer, subtract the offsets.
// If both GEPs are inbounds, then the subtract does not have signed overflow.
if (GEP2) {
Value *Offset = EmitGEPOffset(GEP2);
Result = Builder.CreateSub(Result, Offset, "gepdiff");
Result = Builder.CreateSub(Result, Offset, "gepdiff", /* NUW */ false,
GEP1->isInBounds() && GEP2->isInBounds());
}
// If we have p - gep(p, ...) then we have to negate the result.

16
test/Transforms/InstCombine/sub-gep.ll
View File

@ -245,7 +245,7 @@ define i64 @test24b(i8* %P, i64 %A){
define i64 @test25(i8* %P, i64 %A){
; CHECK-LABEL: @test25(
; CHECK-NEXT: [[B_IDX:%.*]] = shl nsw i64 [[A:%.*]], 1
; CHECK-NEXT: [[GEPDIFF:%.*]] = add i64 [[B_IDX]], -84
; CHECK-NEXT: [[GEPDIFF:%.*]] = add nsw i64 [[B_IDX]], -84
; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%B = getelementptr inbounds [42 x i16], [42 x i16]* @Arr, i64 0, i64 %A
@ -260,7 +260,7 @@ define i16 @test25_as1(i8 addrspace(1)* %P, i64 %A) {
; CHECK-LABEL: @test25_as1(
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[A:%.*]] to i16
; CHECK-NEXT: [[B_IDX:%.*]] = shl nsw i16 [[TMP1]], 1
; CHECK-NEXT: [[GEPDIFF:%.*]] = add i16 [[B_IDX]], -84
; CHECK-NEXT: [[GEPDIFF:%.*]] = add nsw i16 [[B_IDX]], -84
; CHECK-NEXT: ret i16 [[GEPDIFF]]
;
%B = getelementptr inbounds [42 x i16], [42 x i16] addrspace(1)* @Arr_as1, i64 0, i64 %A
@ -272,7 +272,7 @@ define i16 @test25_as1(i8 addrspace(1)* %P, i64 %A) {
define i64 @test30(i8* %foo, i64 %i, i64 %j) {
; CHECK-LABEL: @test30(
; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nsw i64 [[I:%.*]], 2
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub i64 [[GEP1_IDX]], [[J:%.*]]
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub nsw i64 [[GEP1_IDX]], [[J:%.*]]
; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%bit = bitcast i8* %foo to i32*
@ -287,7 +287,7 @@ define i64 @test30(i8* %foo, i64 %i, i64 %j) {
define i16 @test30_as1(i8 addrspace(1)* %foo, i16 %i, i16 %j) {
; CHECK-LABEL: @test30_as1(
; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nsw i16 [[I:%.*]], 2
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub i16 [[GEP1_IDX]], [[J:%.*]]
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub nsw i16 [[GEP1_IDX]], [[J:%.*]]
; CHECK-NEXT: ret i16 [[GEPDIFF]]
;
%bit = bitcast i8 addrspace(1)* %foo to i32 addrspace(1)*
@ -299,9 +299,11 @@ define i16 @test30_as1(i8 addrspace(1)* %foo, i16 %i, i16 %j) {
ret i16 %sub
}
; Inbounds translates to 'nsw' on sub
define i64 @gep_diff_both_inbounds(i8* %foo, i64 %i, i64 %j) {
; CHECK-LABEL: @gep_diff_both_inbounds(
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub i64 [[I:%.*]], [[J:%.*]]
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub nsw i64 [[I:%.*]], [[J:%.*]]
; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%gep1 = getelementptr inbounds i8, i8* %foo, i64 %i
@ -312,6 +314,8 @@ define i64 @gep_diff_both_inbounds(i8* %foo, i64 %i, i64 %j) {
ret i64 %sub
}
; Negative test for 'nsw' - both geps must be inbounds
define i64 @gep_diff_first_inbounds(i8* %foo, i64 %i, i64 %j) {
; CHECK-LABEL: @gep_diff_first_inbounds(
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub i64 [[I:%.*]], [[J:%.*]]
@ -325,6 +329,8 @@ define i64 @gep_diff_first_inbounds(i8* %foo, i64 %i, i64 %j) {
ret i64 %sub
}
; Negative test for 'nsw' - both geps must be inbounds
define i64 @gep_diff_second_inbounds(i8* %foo, i64 %i, i64 %j) {
; CHECK-LABEL: @gep_diff_second_inbounds(
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub i64 [[I:%.*]], [[J:%.*]]

2
test/Transforms/InstCombine/sub.ll
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@ -1077,7 +1077,7 @@ define i64 @test58([100 x [100 x i8]]* %foo, i64 %i, i64 %j) {
; CHECK-LABEL: @test58(
; CHECK-NEXT: [[GEP1_OFFS:%.*]] = add i64 [[I:%.*]], 4200
; CHECK-NEXT: [[GEP2_OFFS:%.*]] = add i64 [[J:%.*]], 4200
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub i64 [[GEP1_OFFS]], [[GEP2_OFFS]]
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub nsw i64 [[GEP1_OFFS]], [[GEP2_OFFS]]
; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%gep1 = getelementptr inbounds [100 x [100 x i8]], [100 x [100 x i8]]* %foo, i64 0, i64 42, i64 %i