[llvm-branch-commits] [llvm] ab29f09 - [InstCombine] propagate 'nsw' on pointer difference of 'inbounds' geps
Sanjay Patel via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Mon Nov 23 13:54:41 PST 2020
Author: Sanjay Patel
Date: 2020-11-23T16:50:09-05:00
New Revision: ab29f091eb64c8608ba943df604b218bcff41a26
URL: https://github.com/llvm/llvm-project/commit/ab29f091eb64c8608ba943df604b218bcff41a26
DIFF: https://github.com/llvm/llvm-project/commit/ab29f091eb64c8608ba943df604b218bcff41a26.diff
LOG: [InstCombine] propagate 'nsw' on pointer difference of 'inbounds' geps
This is a retry of 324a53205. I cautiously reverted that at 6aa3fc4
because the rules about gep math were not clear. Since then, we
have added this line to LangRef for gep inbounds:
"The successive addition of offsets (without adding the base address)
does not wrap the pointer index type in a signed sense (nsw)."
See D90708 and post-commit comments on the revert patch for more details.
Added:
Modified:
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
llvm/test/Transforms/InstCombine/sub-gep.ll
llvm/test/Transforms/InstCombine/sub.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index b8431a5a4532..9a6a790aefaf 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1678,11 +1678,12 @@ 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, "gep
diff ");
+ Result = Builder.CreateSub(Result, Offset, "gep
diff ", /* NUW */ false,
+ GEP1->isInBounds() && GEP2->isInBounds());
}
// If we have p - gep(p, ...) then we have to negate the result.
diff --git a/llvm/test/Transforms/InstCombine/sub-gep.ll b/llvm/test/Transforms/InstCombine/sub-gep.ll
index 9868ed1cdf57..2389b70c3452 100644
--- a/llvm/test/Transforms/InstCombine/sub-gep.ll
+++ b/llvm/test/Transforms/InstCombine/sub-gep.ll
@@ -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:%.*]]
diff --git a/llvm/test/Transforms/InstCombine/sub.ll b/llvm/test/Transforms/InstCombine/sub.ll
index d9c67d0568f7..7809a93f718e 100644
--- a/llvm/test/Transforms/InstCombine/sub.ll
+++ b/llvm/test/Transforms/InstCombine/sub.ll
@@ -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 nsw i64 [[I:%.*]], 4200
; CHECK-NEXT: [[GEP2_OFFS:%.*]] = add nsw 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
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