[llvm] 8b30067 - [InstCombine] improve fold of pointer differences
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Mon Sep 7 12:54:53 PDT 2020
Author: Sanjay Patel
Date: 2020-09-07T15:54:32-04:00
New Revision: 8b300679192b317aa91a28e781fcf60d4416b0d6
URL: https://github.com/llvm/llvm-project/commit/8b300679192b317aa91a28e781fcf60d4416b0d6
DIFF: https://github.com/llvm/llvm-project/commit/8b300679192b317aa91a28e781fcf60d4416b0d6.diff
LOG: [InstCombine] improve fold of pointer differences
This was supposed to be an NFC cleanup, but there's
a real logic difference (did not drop 'nsw') visible
in some tests in addition to an efficiency improvement.
This is because in the case where we have 2 GEPs,
the code was *always* swapping the operands and
negating the result. But if we have 2 GEPs, we
should *never* need swapping/negation AFAICT.
This is part of improving flags propagation noticed
with PR47430.
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 5cf6eb2a885a..5ce32bc592d0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1615,43 +1615,27 @@ Value *InstCombinerImpl::OptimizePointerDifference(Value *LHS, Value *RHS,
// this.
bool Swapped = false;
GEPOperator *GEP1 = nullptr, *GEP2 = nullptr;
+ if (!isa<GEPOperator>(LHS) && isa<GEPOperator>(RHS)) {
+ std::swap(LHS, RHS);
+ Swapped = true;
+ }
- // For now we require one side to be the base pointer "A" or a constant
- // GEP derived from it.
- if (GEPOperator *LHSGEP = dyn_cast<GEPOperator>(LHS)) {
+ // Require at least one GEP with a common base pointer on both sides.
+ if (auto *LHSGEP = dyn_cast<GEPOperator>(LHS)) {
// (gep X, ...) - X
if (LHSGEP->getOperand(0) == RHS) {
GEP1 = LHSGEP;
- Swapped = false;
- } else if (GEPOperator *RHSGEP = dyn_cast<GEPOperator>(RHS)) {
+ } else if (auto *RHSGEP = dyn_cast<GEPOperator>(RHS)) {
// (gep X, ...) - (gep X, ...)
if (LHSGEP->getOperand(0)->stripPointerCasts() ==
- RHSGEP->getOperand(0)->stripPointerCasts()) {
- GEP2 = RHSGEP;
+ RHSGEP->getOperand(0)->stripPointerCasts()) {
GEP1 = LHSGEP;
- Swapped = false;
- }
- }
- }
-
- if (GEPOperator *RHSGEP = dyn_cast<GEPOperator>(RHS)) {
- // X - (gep X, ...)
- if (RHSGEP->getOperand(0) == LHS) {
- GEP1 = RHSGEP;
- Swapped = true;
- } else if (GEPOperator *LHSGEP = dyn_cast<GEPOperator>(LHS)) {
- // (gep X, ...) - (gep X, ...)
- if (RHSGEP->getOperand(0)->stripPointerCasts() ==
- LHSGEP->getOperand(0)->stripPointerCasts()) {
- GEP2 = LHSGEP;
- GEP1 = RHSGEP;
- Swapped = true;
+ GEP2 = RHSGEP;
}
}
}
if (!GEP1)
- // No GEP found.
return nullptr;
if (GEP2) {
diff --git a/llvm/test/Transforms/InstCombine/sub-gep.ll b/llvm/test/Transforms/InstCombine/sub-gep.ll
index fcb24eec349a..f31eeb46d882 100644
--- a/llvm/test/Transforms/InstCombine/sub-gep.ll
+++ b/llvm/test/Transforms/InstCombine/sub-gep.ll
@@ -124,10 +124,10 @@ define i64 @test_inbounds2_nuw_swapped([0 x i32]* %base, i64 %idx) {
; The sub and shl here could be nuw, but this is harder to handle.
define i64 @test_inbounds_nuw_two_gep([0 x i32]* %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @test_inbounds_nuw_two_gep(
+; CHECK-NEXT: [[P2_IDX:%.*]] = shl nsw i64 [[IDX2:%.*]], 2
; CHECK-NEXT: [[P1_IDX_NEG:%.*]] = mul i64 [[IDX:%.*]], -4
-; CHECK-NEXT: [[P2_IDX_NEG_NEG:%.*]] = shl i64 [[IDX2:%.*]], 2
-; CHECK-NEXT: [[GEPDIFF_NEG:%.*]] = add i64 [[P2_IDX_NEG_NEG]], [[P1_IDX_NEG]]
-; CHECK-NEXT: ret i64 [[GEPDIFF_NEG]]
+; CHECK-NEXT: [[GEPDIFF:%.*]] = add i64 [[P1_IDX_NEG]], [[P2_IDX]]
+; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%p1 = getelementptr inbounds [0 x i32], [0 x i32]* %base, i64 0, i64 %idx
%p2 = getelementptr inbounds [0 x i32], [0 x i32]* %base, i64 0, i64 %idx2
diff --git a/llvm/test/Transforms/InstCombine/sub.ll b/llvm/test/Transforms/InstCombine/sub.ll
index dbe1631226d6..437d8f8c5c02 100644
--- a/llvm/test/Transforms/InstCombine/sub.ll
+++ b/llvm/test/Transforms/InstCombine/sub.ll
@@ -505,9 +505,9 @@ define i64 @test24b(i8* %P, i64 %A){
define i64 @test25(i8* %P, i64 %A){
; CHECK-LABEL: @test25(
-; CHECK-NEXT: [[B_IDX_NEG_NEG:%.*]] = shl i64 [[A:%.*]], 1
-; CHECK-NEXT: [[GEPDIFF_NEG:%.*]] = add i64 [[B_IDX_NEG_NEG]], -84
-; CHECK-NEXT: ret i64 [[GEPDIFF_NEG]]
+; CHECK-NEXT: [[B_IDX:%.*]] = shl nsw i64 [[A:%.*]], 1
+; CHECK-NEXT: [[GEPDIFF:%.*]] = add i64 [[B_IDX]], -84
+; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%B = getelementptr inbounds [42 x i16], [42 x i16]* @Arr, i64 0, i64 %A
%C = ptrtoint i16* %B to i64
@@ -520,9 +520,9 @@ define i64 @test25(i8* %P, i64 %A){
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_NEG_NEG:%.*]] = shl i16 [[TMP1]], 1
-; CHECK-NEXT: [[GEPDIFF_NEG:%.*]] = add i16 [[B_IDX_NEG_NEG]], -84
-; CHECK-NEXT: ret i16 [[GEPDIFF_NEG]]
+; CHECK-NEXT: [[B_IDX:%.*]] = shl nsw i16 [[TMP1]], 1
+; CHECK-NEXT: [[GEPDIFF:%.*]] = add 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
%C = ptrtoint i16 addrspace(1)* %B to i16
@@ -825,8 +825,8 @@ define i32 @test28commuted(i32 %x, i32 %y, i32 %z) {
define i64 @test29(i8* %foo, i64 %i, i64 %j) {
; CHECK-LABEL: @test29(
-; CHECK-NEXT: [[GEPDIFF_NEG:%.*]] = sub i64 [[I:%.*]], [[J:%.*]]
-; CHECK-NEXT: ret i64 [[GEPDIFF_NEG]]
+; CHECK-NEXT: [[GEPDIFF:%.*]] = sub i64 [[I:%.*]], [[J:%.*]]
+; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%gep1 = getelementptr inbounds i8, i8* %foo, i64 %i
%gep2 = getelementptr inbounds i8, i8* %foo, i64 %j
@@ -838,9 +838,9 @@ define i64 @test29(i8* %foo, i64 %i, i64 %j) {
define i64 @test30(i8* %foo, i64 %i, i64 %j) {
; CHECK-LABEL: @test30(
-; CHECK-NEXT: [[GEP1_IDX_NEG_NEG:%.*]] = shl i64 [[I:%.*]], 2
-; CHECK-NEXT: [[GEPDIFF_NEG:%.*]] = sub i64 [[GEP1_IDX_NEG_NEG]], [[J:%.*]]
-; CHECK-NEXT: ret i64 [[GEPDIFF_NEG]]
+; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nsw i64 [[I:%.*]], 2
+; CHECK-NEXT: [[GEPDIFF:%.*]] = sub i64 [[GEP1_IDX]], [[J:%.*]]
+; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%bit = bitcast i8* %foo to i32*
%gep1 = getelementptr inbounds i32, i32* %bit, i64 %i
@@ -853,9 +853,9 @@ 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_NEG_NEG:%.*]] = shl i16 [[I:%.*]], 2
-; CHECK-NEXT: [[GEPDIFF_NEG:%.*]] = sub i16 [[GEP1_IDX_NEG_NEG]], [[J:%.*]]
-; CHECK-NEXT: ret i16 [[GEPDIFF_NEG]]
+; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nsw i16 [[I:%.*]], 2
+; CHECK-NEXT: [[GEPDIFF:%.*]] = sub i16 [[GEP1_IDX]], [[J:%.*]]
+; CHECK-NEXT: ret i16 [[GEPDIFF]]
;
%bit = bitcast i8 addrspace(1)* %foo to i32 addrspace(1)*
%gep1 = getelementptr inbounds i32, i32 addrspace(1)* %bit, i16 %i
@@ -1234,10 +1234,10 @@ define i64 @test58([100 x [100 x i8]]* %foo, i64 %i, i64 %j) {
; "%sub = i64 %i, %j, ret i64 %sub"
; gep1 and gep2 have only one use
; CHECK-LABEL: @test58(
-; CHECK-NEXT: [[GEP2_OFFS:%.*]] = add i64 [[J:%.*]], 4200
; CHECK-NEXT: [[GEP1_OFFS:%.*]] = add i64 [[I:%.*]], 4200
-; CHECK-NEXT: [[GEPDIFF_NEG:%.*]] = sub i64 [[GEP1_OFFS]], [[GEP2_OFFS]]
-; CHECK-NEXT: ret i64 [[GEPDIFF_NEG]]
+; CHECK-NEXT: [[GEP2_OFFS:%.*]] = add i64 [[J:%.*]], 4200
+; CHECK-NEXT: [[GEPDIFF:%.*]] = sub 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
%gep2 = getelementptr inbounds [100 x [100 x i8]], [100 x [100 x i8]]* %foo, i64 0, i64 42, i64 %j
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