[InstCombine] Fold icmp of gep chain with base #144065
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@llvm/pr-subscribers-llvm-transforms Author: Nikita Popov (nikic) ChangesFold icmp between a chain of geps and its base pointer. Previously only a single gep was supported. This will be extended to handle the case of two gep chains with a common base in a followup. This helps to avoid regressions after #137297. Full diff: https://github.com/llvm/llvm-project/pull/144065.diff 4 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index c112fae351817..60cd93f9e2d42 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -708,10 +708,12 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
return I;
};
- Value *PtrBase = GEPLHS->getOperand(0);
- if (PtrBase == RHS && CanFold(GEPLHS->getNoWrapFlags())) {
+ CommonPointerBase Base = CommonPointerBase::compute(GEPLHS, RHS);
+ if (Base.Ptr == RHS && CanFold(Base.LHSNW)) {
// ((gep Ptr, OFFSET) cmp Ptr) ---> (OFFSET cmp 0).
- Value *Offset = EmitGEPOffset(GEPLHS);
+ Type *IdxTy = DL.getIndexType(GEPLHS->getType());
+ Value *Offset =
+ EmitGEPOffsets(Base.LHSGEPs, Base.LHSNW, IdxTy, /*RewriteGEPs=*/false);
return NewICmp(GEPLHS->getNoWrapFlags(), Offset,
Constant::getNullValue(Offset->getType()));
}
@@ -750,6 +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)) {
bool IndicesTheSame =
GEPLHS->getNumOperands() == GEPRHS->getNumOperands() &&
diff --git a/llvm/test/Transforms/InstCombine/getelementptr.ll b/llvm/test/Transforms/InstCombine/getelementptr.ll
index 61236df80bfa6..23e682f5217cd 100644
--- a/llvm/test/Transforms/InstCombine/getelementptr.ll
+++ b/llvm/test/Transforms/InstCombine/getelementptr.ll
@@ -694,7 +694,7 @@ define i32 @test28() nounwind {
; CHECK-NEXT: [[TMP0:%.*]] = sext i32 [[T12_REC]] to i64
; CHECK-NEXT: [[T12:%.*]] = getelementptr inbounds [[STRUCT_X:%.*]], ptr [[T45]], i64 [[TMP0]]
; CHECK-NEXT: [[T16:%.*]] = call i32 (ptr, ...) @printf(ptr noundef nonnull dereferenceable(1) @.str1, ptr nonnull [[T12]]) #[[ATTR0]]
-; CHECK-NEXT: [[T84:%.*]] = icmp eq ptr [[T12]], [[ORIENTATIONS]]
+; CHECK-NEXT: [[T84:%.*]] = icmp eq i32 [[INDVAR]], 0
; CHECK-NEXT: [[INDVAR_NEXT]] = add i32 [[INDVAR]], 1
; CHECK-NEXT: br i1 [[T84]], label [[BB17:%.*]], label [[BB10]]
; CHECK: bb17:
diff --git a/llvm/test/Transforms/InstCombine/icmp-gep.ll b/llvm/test/Transforms/InstCombine/icmp-gep.ll
index 7f8f1ae73948d..c2ec3bc83e066 100644
--- a/llvm/test/Transforms/InstCombine/icmp-gep.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-gep.ll
@@ -757,3 +757,67 @@ define i1 @gep_diff_base_same_indices_nuw_nusw(ptr %x, ptr %y, i64 %z) {
%cmp = icmp ult ptr %gep1, %gep2
ret i1 %cmp
}
+
+define i1 @gep_multiple_eq(ptr %base, i64 %idx, i64 %idx2) {
+; CHECK-LABEL: @gep_multiple_eq(
+; CHECK-NEXT: [[GEP1_IDX1:%.*]] = add i64 [[IDX:%.*]], [[IDX2:%.*]]
+; CHECK-NEXT: [[DOTMASK:%.*]] = and i64 [[GEP1_IDX1]], 4611686018427387903
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[DOTMASK]], 0
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %gep1 = getelementptr i32, ptr %base, i64 %idx
+ %gep2 = getelementptr i32, ptr %gep1, i64 %idx2
+ %cmp = icmp eq ptr %gep2, %base
+ ret i1 %cmp
+}
+
+define i1 @gep_multiple_eq_commuted(ptr %base, i64 %idx, i64 %idx2) {
+; CHECK-LABEL: @gep_multiple_eq_commuted(
+; CHECK-NEXT: [[GEP1_IDX1:%.*]] = add i64 [[IDX:%.*]], [[IDX2:%.*]]
+; CHECK-NEXT: [[DOTMASK:%.*]] = and i64 [[GEP1_IDX1]], 4611686018427387903
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[DOTMASK]], 0
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %gep1 = getelementptr i32, ptr %base, i64 %idx
+ %gep2 = getelementptr i32, ptr %gep1, i64 %idx2
+ %cmp = icmp eq ptr %base, %gep2
+ ret i1 %cmp
+}
+
+define i1 @gep_mugtiple_ugt_nuw(ptr %base, i64 %idx, i64 %idx2) {
+; CHECK-LABEL: @gep_mugtiple_ugt_nuw(
+; CHECK-NEXT: [[GEP1_IDX1:%.*]] = sub i64 0, [[IDX2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ne i64 [[IDX:%.*]], [[GEP1_IDX1]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %gep1 = getelementptr nuw i32, ptr %base, i64 %idx
+ %gep2 = getelementptr nuw i32, ptr %gep1, i64 %idx2
+ %cmp = icmp ugt ptr %gep2, %base
+ ret i1 %cmp
+}
+
+define i1 @gep_mugtiple_ugt_not_all_nuw(ptr %base, i64 %idx, i64 %idx2) {
+; CHECK-LABEL: @gep_mugtiple_ugt_not_all_nuw(
+; CHECK-NEXT: [[GEP1:%.*]] = getelementptr nuw i32, ptr [[BASE:%.*]], i64 [[IDX:%.*]]
+; CHECK-NEXT: [[GEP2:%.*]] = getelementptr i32, ptr [[GEP1]], i64 [[IDX2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt ptr [[GEP2]], [[BASE]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %gep1 = getelementptr nuw i32, ptr %base, i64 %idx
+ %gep2 = getelementptr i32, ptr %gep1, i64 %idx2
+ %cmp = icmp ugt ptr %gep2, %base
+ ret i1 %cmp
+}
+
+define i1 @gep_mugtiple_ugt_inbounds_nusw(ptr %base, i64 %idx, i64 %idx2) {
+; CHECK-LABEL: @gep_mugtiple_ugt_inbounds_nusw(
+; CHECK-NEXT: [[GEP1_IDX1:%.*]] = add i64 [[IDX:%.*]], [[IDX2:%.*]]
+; CHECK-NEXT: [[TMP1:%.*]] = shl i64 [[GEP1_IDX1]], 2
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i64 [[TMP1]], 0
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %gep1 = getelementptr inbounds i32, ptr %base, i64 %idx
+ %gep2 = getelementptr nusw i32, ptr %gep1, i64 %idx2
+ %cmp = icmp ugt ptr %gep2, %base
+ ret i1 %cmp
+}
diff --git a/llvm/test/Transforms/InstCombine/pr39908.ll b/llvm/test/Transforms/InstCombine/pr39908.ll
index ca143f417fb27..5d13a331c6d2e 100644
--- a/llvm/test/Transforms/InstCombine/pr39908.ll
+++ b/llvm/test/Transforms/InstCombine/pr39908.ll
@@ -7,9 +7,7 @@ target datalayout = "p:32:32"
define i1 @test(ptr %p, i32 %n) {
; CHECK-LABEL: @test(
-; CHECK-NEXT: [[END:%.*]] = getelementptr inbounds [0 x %S], ptr [[P:%.*]], i32 0, i32 [[N:%.*]], i32 0, i32 0
-; CHECK-NEXT: [[LAST:%.*]] = getelementptr inbounds i8, ptr [[END]], i32 -8
-; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[LAST]], [[P]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[N:%.*]], 1
; CHECK-NEXT: ret i1 [[CMP]]
;
%end = getelementptr inbounds [0 x %S], ptr %p, i32 0, i32 %n, i32 0, i32 0
@@ -22,9 +20,7 @@ define i1 @test(ptr %p, i32 %n) {
define i1 @test64(ptr %p, i64 %n) {
; CHECK-LABEL: @test64(
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[N:%.*]] to i32
-; CHECK-NEXT: [[END:%.*]] = getelementptr inbounds [0 x %S], ptr [[P:%.*]], i32 0, i32 [[TMP1]], i32 0, i32 0
-; CHECK-NEXT: [[LAST:%.*]] = getelementptr inbounds i8, ptr [[END]], i32 -8
-; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[LAST]], [[P]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[TMP1]], 1
; CHECK-NEXT: ret i1 [[CMP]]
;
%end = getelementptr inbounds [0 x %S], ptr %p, i64 0, i64 %n, i32 0, i64 0
@@ -37,9 +33,7 @@ define i1 @test64(ptr %p, i64 %n) {
define i1 @test64_overflow(ptr %p, i64 %n) {
; CHECK-LABEL: @test64_overflow(
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[N:%.*]] to i32
-; CHECK-NEXT: [[END:%.*]] = getelementptr inbounds [0 x %S], ptr [[P:%.*]], i32 0, i32 [[TMP1]], i32 0, i32 0
-; CHECK-NEXT: [[LAST:%.*]] = getelementptr inbounds i8, ptr [[END]], i32 -8
-; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[LAST]], [[P]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[TMP1]], 1
; CHECK-NEXT: ret i1 [[CMP]]
;
%end = getelementptr inbounds [0 x %S], ptr %p, i64 0, i64 %n, i32 0, i64 8589934592
|
dtcxzyw
approved these changes
Jun 27, 2025
| Value *Offset = EmitGEPOffset(GEPLHS); | ||
| Type *IdxTy = DL.getIndexType(GEPLHS->getType()); | ||
| Value *Offset = | ||
| EmitGEPOffsets(Base.LHSGEPs, Base.LHSNW, IdxTy, /*RewriteGEPs=*/false); |
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Suggested change
| EmitGEPOffsets(Base.LHSGEPs, Base.LHSNW, IdxTy, /*RewriteGEPs=*/false); | |
| EmitGEPOffsets(Base.LHSGEPs, Base.LHSNW, IdxTy, /*RewriteGEPs=*/true); |
Rewrite GEPs to avoid duplicating the arithmetic: dtcxzyw/llvm-opt-benchmark#2510
We can land this later together with
llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
Lines 2156 to 2159 in 5fdcb35
Fold icmp between a chain of geps and its based pointer. Previously only a single gep was supported. This will be extended to handle the case of two gep chains with a common base in a followup.
dtcxzyw
approved these changes
Jul 2, 2025
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/138/builds/15445 Here is the relevant piece of the build log for the reference |
nikic
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Jul 23, 2025
This extends #144065 to the general case of an icmp between two GEP chains that have a common base.
llvm-sync bot
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Jul 23, 2025
This extends llvm/llvm-project#144065 to the general case of an icmp between two GEP chains that have a common base.
mahesh-attarde
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that referenced
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Jul 28, 2025
This extends llvm#144065 to the general case of an icmp between two GEP chains that have a common base.
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Fold icmp between a chain of geps and its base pointer. Previously only a single gep was supported.
This will be extended to handle the case of two gep chains with a common base in a followup.
This helps to avoid regressions after #137297.