Skip to content

[InstCombine] Fold icmp of gep chains #146714

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 2 commits into
base: main
Choose a base branch
from
+159 −13
Open

[InstCombine] Fold icmp of gep chains #146714

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
11ed143
Add tests for icmp of gep chains with common base
nikic Jul 2, 2025
91fc73e
support folding icmp of gep chains with common base
nikic Jun 12, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
24 changes: 11 additions & 13 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -752,8 +752,7 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,

// If the base pointers are different, but the indices are the same, just
// compare the base pointer.
Value *PtrBase = GEPLHS->getOperand(0);
if (PtrBase != GEPRHS->getOperand(0)) {
if (GEPLHS->getOperand(0) != GEPRHS->getOperand(0)) {
bool IndicesTheSame =
GEPLHS->getNumOperands() == GEPRHS->getNumOperands() &&
GEPLHS->getPointerOperand()->getType() ==
Expand All @@ -779,7 +778,7 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
if (GEPLHS->isInBounds() && GEPRHS->isInBounds() &&
(GEPLHS->hasAllConstantIndices() || GEPLHS->hasOneUse()) &&
(GEPRHS->hasAllConstantIndices() || GEPRHS->hasOneUse()) &&
PtrBase->stripPointerCasts() ==
GEPLHS->getOperand(0)->stripPointerCasts() ==
GEPRHS->getOperand(0)->stripPointerCasts() &&
!GEPLHS->getType()->isVectorTy()) {
Value *LOffset = EmitGEPOffset(GEPLHS);
Expand All @@ -802,14 +801,10 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
LOffset, ROffset);
return replaceInstUsesWith(I, Cmp);
}

// Otherwise, the base pointers are different and the indices are
// different. Try convert this to an indexed compare by looking through
// PHIs/casts.
return transformToIndexedCompare(GEPLHS, RHS, Cond, DL, *this);
}

if (GEPLHS->getNumOperands() == GEPRHS->getNumOperands() &&
if (GEPLHS->getOperand(0) == GEPRHS->getOperand(0) &&
GEPLHS->getNumOperands() == GEPRHS->getNumOperands() &&
GEPLHS->getSourceElementType() == GEPRHS->getSourceElementType()) {
// If the GEPs only differ by one index, compare it.
unsigned NumDifferences = 0; // Keep track of # differences.
Expand Down Expand Up @@ -846,11 +841,14 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
}
}

if (CanFold(NW)) {
if (Base.Ptr && CanFold(Base.LHSNW & Base.RHSNW)) {
// ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2) ---> (OFFSET1 cmp OFFSET2)
Value *L = EmitGEPOffset(GEPLHS, /*RewriteGEP=*/true);
Value *R = EmitGEPOffset(GEPRHS, /*RewriteGEP=*/true);
return NewICmp(NW, L, R);
Type *IdxTy = DL.getIndexType(GEPLHS->getType());
Value *L =
EmitGEPOffsets(Base.LHSGEPs, Base.LHSNW, IdxTy, /*RewriteGEP=*/true);
Value *R =
EmitGEPOffsets(Base.RHSGEPs, Base.RHSNW, IdxTy, /*RewriteGEP=*/true);
return NewICmp(Base.LHSNW & Base.RHSNW, L, R);
}
}

Expand Down
148 changes: 148 additions & 0 deletions llvm/test/Transforms/InstCombine/icmp-gep.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -849,3 +849,151 @@ define i1 @gep_mugtiple_ugt_inbounds_nusw(ptr %base, i64 %idx, i64 %idx2) {
%cmp = icmp ugt ptr %gep2, %base
ret i1 %cmp
}

define i1 @gep_gep_multiple_eq(ptr %base, i64 %idx1, i64 %idx2, i64 %idx3, i64 %idx4) {
; CHECK-LABEL: @gep_gep_multiple_eq(
; CHECK-NEXT: [[GEP1_IDX1:%.*]] = add i64 [[IDX1:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: [[GEP3_IDX2:%.*]] = add i64 [[IDX3:%.*]], [[IDX4:%.*]]
; CHECK-NEXT: [[CMP_UNSHIFTED:%.*]] = xor i64 [[GEP1_IDX1]], [[GEP3_IDX2]]
; CHECK-NEXT: [[CMP_MASK:%.*]] = and i64 [[CMP_UNSHIFTED]], 4611686018427387903
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[CMP_MASK]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr i32, ptr %base, i64 %idx1
%gep2 = getelementptr i32, ptr %gep1, i64 %idx2
%gep3 = getelementptr i32, ptr %base, i64 %idx3
%gep4 = getelementptr i32, ptr %gep3, i64 %idx4
%cmp = icmp eq ptr %gep2, %gep4
ret i1 %cmp
}

define i1 @gep_gep_multiple_eq_nuw(ptr %base, i64 %idx1, i64 %idx2, i64 %idx3, i64 %idx4) {
; CHECK-LABEL: @gep_gep_multiple_eq_nuw(
; CHECK-NEXT: [[GEP1_IDX1:%.*]] = add i64 [[IDX1:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: [[GEP3_IDX2:%.*]] = add i64 [[IDX3:%.*]], [[IDX4:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[GEP1_IDX1]], [[GEP3_IDX2]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr nuw i32, ptr %base, i64 %idx1
%gep2 = getelementptr nuw i32, ptr %gep1, i64 %idx2
%gep3 = getelementptr nuw i32, ptr %base, i64 %idx3
%gep4 = getelementptr nuw i32, ptr %gep3, i64 %idx4
%cmp = icmp eq ptr %gep2, %gep4
ret i1 %cmp
}

define i1 @gep_gep_multiple_eq_nuw_different_scales(ptr %base, i64 %idx1, i64 %idx2, i64 %idx3, i64 %idx4) {
; CHECK-LABEL: @gep_gep_multiple_eq_nuw_different_scales(
; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nuw i64 [[IDX1:%.*]], 2
; CHECK-NEXT: [[GEP2_IDX:%.*]] = shl nuw i64 [[IDX2:%.*]], 3
; CHECK-NEXT: [[GEP3_IDX:%.*]] = shl nuw i64 [[IDX3:%.*]], 2
; CHECK-NEXT: [[GEP4_IDX:%.*]] = shl nuw i64 [[IDX4:%.*]], 3
; CHECK-NEXT: [[TMP1:%.*]] = add nuw i64 [[GEP1_IDX]], [[GEP2_IDX]]
; CHECK-NEXT: [[TMP2:%.*]] = add nuw i64 [[GEP3_IDX]], [[GEP4_IDX]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[TMP1]], [[TMP2]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr nuw i32, ptr %base, i64 %idx1
%gep2 = getelementptr nuw i64, ptr %gep1, i64 %idx2
%gep3 = getelementptr nuw i32, ptr %base, i64 %idx3
%gep4 = getelementptr nuw i64, ptr %gep3, i64 %idx4
%cmp = icmp eq ptr %gep2, %gep4
ret i1 %cmp
}

define i1 @gep_gep_multiple_eq_partial_nuw_different_scales(ptr %base, i64 %idx1, i64 %idx2, i64 %idx3, i64 %idx4) {
; CHECK-LABEL: @gep_gep_multiple_eq_partial_nuw_different_scales(
; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nuw i64 [[IDX1:%.*]], 2
; CHECK-NEXT: [[GEP2_IDX:%.*]] = shl nuw i64 [[IDX2:%.*]], 3
; CHECK-NEXT: [[GEP3_IDX:%.*]] = shl nuw i64 [[IDX3:%.*]], 2
; CHECK-NEXT: [[GEP4_IDX:%.*]] = shl i64 [[IDX4:%.*]], 3
; CHECK-NEXT: [[TMP1:%.*]] = add nuw i64 [[GEP1_IDX]], [[GEP2_IDX]]
; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[GEP3_IDX]], [[GEP4_IDX]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[TMP1]], [[TMP2]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr nuw i32, ptr %base, i64 %idx1
%gep2 = getelementptr nuw i64, ptr %gep1, i64 %idx2
%gep3 = getelementptr nuw i32, ptr %base, i64 %idx3
%gep4 = getelementptr i64, ptr %gep3, i64 %idx4
%cmp = icmp eq ptr %gep2, %gep4
ret i1 %cmp
}

define i1 @gep_gep_multiple_eq_partial_inbounds_different_scales(ptr %base, i64 %idx1, i64 %idx2, i64 %idx3, i64 %idx4) {
; CHECK-LABEL: @gep_gep_multiple_eq_partial_inbounds_different_scales(
; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nsw i64 [[IDX1:%.*]], 2
; CHECK-NEXT: [[GEP2_IDX:%.*]] = shl nsw i64 [[IDX2:%.*]], 3
; CHECK-NEXT: [[GEP3_IDX:%.*]] = shl nsw i64 [[IDX3:%.*]], 2
; CHECK-NEXT: [[GEP4_IDX:%.*]] = shl i64 [[IDX4:%.*]], 3
; CHECK-NEXT: [[TMP1:%.*]] = add nsw i64 [[GEP1_IDX]], [[GEP2_IDX]]
; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[GEP3_IDX]], [[GEP4_IDX]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[TMP1]], [[TMP2]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr inbounds i32, ptr %base, i64 %idx1
%gep2 = getelementptr inbounds i64, ptr %gep1, i64 %idx2
%gep3 = getelementptr inbounds i32, ptr %base, i64 %idx3
%gep4 = getelementptr i64, ptr %gep3, i64 %idx4
%cmp = icmp eq ptr %gep2, %gep4
ret i1 %cmp
}

define i1 @gep_gep_multiple_ult_nuw(ptr %base, i64 %idx1, i64 %idx2, i64 %idx3, i64 %idx4) {
; CHECK-LABEL: @gep_gep_multiple_ult_nuw(
; CHECK-NEXT: [[GEP1_IDX1:%.*]] = add i64 [[IDX1:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: [[GEP3_IDX2:%.*]] = add i64 [[IDX3:%.*]], [[IDX4:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[GEP1_IDX1]], [[GEP3_IDX2]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr nuw i32, ptr %base, i64 %idx1
%gep2 = getelementptr nuw i32, ptr %gep1, i64 %idx2
%gep3 = getelementptr nuw i32, ptr %base, i64 %idx3
%gep4 = getelementptr nuw i32, ptr %gep3, i64 %idx4
%cmp = icmp ult ptr %gep2, %gep4
ret i1 %cmp
}

define i1 @gep_gep_multiple_ult_missing_nuw(ptr %base, i64 %idx1, i64 %idx2, i64 %idx3, i64 %idx4) {
; CHECK-LABEL: @gep_gep_multiple_ult_missing_nuw(
; CHECK-NEXT: [[GEP1:%.*]] = getelementptr nuw i32, ptr [[BASE:%.*]], i64 [[IDX1:%.*]]
; CHECK-NEXT: [[GEP2:%.*]] = getelementptr nuw i32, ptr [[GEP1]], i64 [[IDX2:%.*]]
; CHECK-NEXT: [[GEP3:%.*]] = getelementptr nuw i32, ptr [[BASE]], i64 [[IDX3:%.*]]
; CHECK-NEXT: [[GEP4:%.*]] = getelementptr i32, ptr [[GEP3]], i64 [[IDX4:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ult ptr [[GEP2]], [[GEP4]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr nuw i32, ptr %base, i64 %idx1
%gep2 = getelementptr nuw i32, ptr %gep1, i64 %idx2
%gep3 = getelementptr nuw i32, ptr %base, i64 %idx3
%gep4 = getelementptr i32, ptr %gep3, i64 %idx4
%cmp = icmp ult ptr %gep2, %gep4
ret i1 %cmp
}

define i1 @gep_gep_multiple_ult_nuw_multi_use(ptr %base, i64 %idx1, i64 %idx2, i64 %idx3, i64 %idx4) {
; CHECK-LABEL: @gep_gep_multiple_ult_nuw_multi_use(
; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nuw i64 [[IDX1:%.*]], 2
; CHECK-NEXT: [[GEP1:%.*]] = getelementptr nuw i8, ptr [[BASE:%.*]], i64 [[GEP1_IDX]]
; CHECK-NEXT: [[GEP2_IDX:%.*]] = shl nuw i64 [[IDX2:%.*]], 2
; CHECK-NEXT: [[GEP2:%.*]] = getelementptr nuw i8, ptr [[GEP1]], i64 [[GEP2_IDX]]
; CHECK-NEXT: [[GEP3_IDX:%.*]] = shl nuw i64 [[IDX3:%.*]], 2
; CHECK-NEXT: [[GEP3:%.*]] = getelementptr nuw i8, ptr [[BASE]], i64 [[GEP3_IDX]]
; CHECK-NEXT: [[GEP4_IDX:%.*]] = shl nuw i64 [[IDX4:%.*]], 2
; CHECK-NEXT: [[GEP5:%.*]] = getelementptr nuw i8, ptr [[GEP3]], i64 [[GEP4_IDX]]
; CHECK-NEXT: call void @use(ptr [[GEP2]])
; CHECK-NEXT: call void @use(ptr [[GEP5]])
; CHECK-NEXT: [[TMP1:%.*]] = add nuw i64 [[GEP1_IDX]], [[GEP2_IDX]]
; CHECK-NEXT: [[TMP2:%.*]] = add nuw i64 [[GEP3_IDX]], [[GEP4_IDX]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[TMP1]], [[TMP2]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr nuw i32, ptr %base, i64 %idx1
%gep2 = getelementptr nuw i32, ptr %gep1, i64 %idx2
%gep3 = getelementptr nuw i32, ptr %base, i64 %idx3
%gep4 = getelementptr nuw i32, ptr %gep3, i64 %idx4
call void @use(ptr %gep2)
call void @use(ptr %gep4)
%cmp = icmp ult ptr %gep2, %gep4
ret i1 %cmp
}
Loading