[llvm] [InstCombine] Support gep nuw in icmp folds (PR #118472)
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Tue Dec 3 03:32:50 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Nikita Popov (nikic)
<details>
<summary>Changes</summary>
Unsigned icmp of gep nuw folds to unsigned icmp of offsets. Unsigned icmp of gep nusw nuw folds to unsigned samesign icmp of offsets.
Proofs: https://alive2.llvm.org/ce/z/VEwQY8
---
Full diff: https://github.com/llvm/llvm-project/pull/118472.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp (+27-9)
- (modified) llvm/test/Transforms/InstCombine/icmp-gep.ll (+75)
``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 579214c28fc304..ffc0b33171b8fc 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -690,13 +690,32 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
if (!isa<GetElementPtrInst>(RHS))
RHS = RHS->stripPointerCasts();
+ auto CanFold = [Cond](GEPNoWrapFlags NW) {
+ if (ICmpInst::isEquality(Cond))
+ return true;
+
+ // Unsigned predicates can be folded if the GEPs have *any* nowrap flags.
+ assert(ICmpInst::isUnsigned(Cond));
+ return NW != GEPNoWrapFlags::none();
+ };
+
+ auto NewICmp = [Cond](GEPNoWrapFlags NW, Value *Op1, Value *Op2) {
+ if (!NW.hasNoUnsignedWrap()) {
+ // Convert signed to unsigned comparison.
+ return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Op1, Op2);
+ }
+
+ auto *I = new ICmpInst(Cond, Op1, Op2);
+ I->setSameSign(NW.hasNoUnsignedSignedWrap());
+ return I;
+ };
+
Value *PtrBase = GEPLHS->getOperand(0);
- if (PtrBase == RHS &&
- (GEPLHS->hasNoUnsignedSignedWrap() || ICmpInst::isEquality(Cond))) {
+ if (PtrBase == RHS && CanFold(GEPLHS->getNoWrapFlags())) {
// ((gep Ptr, OFFSET) cmp Ptr) ---> (OFFSET cmp 0).
Value *Offset = EmitGEPOffset(GEPLHS);
- return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Offset,
- Constant::getNullValue(Offset->getType()));
+ return NewICmp(GEPLHS->getNoWrapFlags(), Offset,
+ Constant::getNullValue(Offset->getType()));
}
if (GEPLHS->isInBounds() && ICmpInst::isEquality(Cond) &&
@@ -814,19 +833,18 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
return replaceInstUsesWith(I, // No comparison is needed here.
ConstantInt::get(I.getType(), ICmpInst::isTrueWhenEqual(Cond)));
- else if (NumDifferences == 1 && NW.hasNoUnsignedSignedWrap()) {
+ else if (NumDifferences == 1 && CanFold(NW)) {
Value *LHSV = GEPLHS->getOperand(DiffOperand);
Value *RHSV = GEPRHS->getOperand(DiffOperand);
- // Make sure we do a signed comparison here.
- return new ICmpInst(ICmpInst::getSignedPredicate(Cond), LHSV, RHSV);
+ return NewICmp(NW, LHSV, RHSV);
}
}
- if (NW.hasNoUnsignedSignedWrap() || CmpInst::isEquality(Cond)) {
+ if (CanFold(NW)) {
// ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2) ---> (OFFSET1 cmp OFFSET2)
Value *L = EmitGEPOffset(GEPLHS, /*RewriteGEP=*/true);
Value *R = EmitGEPOffset(GEPRHS, /*RewriteGEP=*/true);
- return new ICmpInst(ICmpInst::getSignedPredicate(Cond), L, R);
+ return NewICmp(NW, L, R);
}
}
diff --git a/llvm/test/Transforms/InstCombine/icmp-gep.ll b/llvm/test/Transforms/InstCombine/icmp-gep.ll
index 1545d034b2ac31..1bc000cd6ebf1e 100644
--- a/llvm/test/Transforms/InstCombine/icmp-gep.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-gep.ll
@@ -143,6 +143,44 @@ define i1 @ult_base_nusw(ptr %x, i64 %y) {
ret i1 %r
}
+define i1 @ugt_base_nuw(ptr %x, i64 %y) {
+; CHECK-LABEL: @ugt_base_nuw(
+; CHECK-NEXT: [[R:%.*]] = icmp ne i64 [[Y:%.*]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %g = getelementptr nuw i8, ptr %x, i64 %y
+ %r = icmp ugt ptr %g, %x
+ ret i1 %r
+}
+
+define i1 @ugt_base_nusw_nuw(ptr %x, i64 %y) {
+; CHECK-LABEL: @ugt_base_nusw_nuw(
+; CHECK-NEXT: [[R:%.*]] = icmp ne i64 [[Y:%.*]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %g = getelementptr nusw nuw i8, ptr %x, i64 %y
+ %r = icmp ugt ptr %g, %x
+ ret i1 %r
+}
+
+define i1 @uge_base_nuw(ptr %x, i64 %y) {
+; CHECK-LABEL: @uge_base_nuw(
+; CHECK-NEXT: ret i1 true
+;
+ %g = getelementptr nuw i8, ptr %x, i64 %y
+ %r = icmp uge ptr %g, %x
+ ret i1 %r
+}
+
+define i1 @uge_base_nusw_nuw(ptr %x, i64 %y) {
+; CHECK-LABEL: @uge_base_nusw_nuw(
+; CHECK-NEXT: ret i1 true
+;
+ %g = getelementptr nusw nuw i8, ptr %x, i64 %y
+ %r = icmp uge ptr %g, %x
+ ret i1 %r
+}
+
define i1 @ugt_base_inbounds_commute(i64 %y) {
; CHECK-LABEL: @ugt_base_inbounds_commute(
; CHECK-NEXT: [[X:%.*]] = call ptr @getptr()
@@ -319,6 +357,43 @@ define i1 @test60_nusw_inbounds(ptr %foo, i64 %i, i64 %j) {
ret i1 %cmp
}
+define i1 @test60_nuw(ptr %foo, i64 %i, i64 %j) {
+; CHECK-LABEL: @test60_nuw(
+; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nuw i64 [[I:%.*]], 2
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[GEP1_IDX]], [[J:%.*]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %gep1 = getelementptr nuw i32, ptr %foo, i64 %i
+ %gep2 = getelementptr nuw i8, ptr %foo, i64 %j
+ %cmp = icmp ult ptr %gep1, %gep2
+ ret i1 %cmp
+}
+
+define i1 @test60_nusw_nuw(ptr %foo, i64 %i, i64 %j) {
+; CHECK-LABEL: @test60_nusw_nuw(
+; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nuw nsw i64 [[I:%.*]], 2
+; CHECK-NEXT: [[CMP:%.*]] = icmp samesign ult i64 [[GEP1_IDX]], [[J:%.*]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %gep1 = getelementptr nusw nuw i32, ptr %foo, i64 %i
+ %gep2 = getelementptr nusw nuw i8, ptr %foo, i64 %j
+ %cmp = icmp ult ptr %gep1, %gep2
+ ret i1 %cmp
+}
+
+define i1 @test60_nusw_nuw_mix(ptr %foo, i64 %i, i64 %j) {
+; CHECK-LABEL: @test60_nusw_nuw_mix(
+; CHECK-NEXT: [[GEP1:%.*]] = getelementptr nuw i32, ptr [[FOO:%.*]], i64 [[I:%.*]]
+; CHECK-NEXT: [[GEP2:%.*]] = getelementptr nusw i8, ptr [[FOO]], i64 [[J:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult ptr [[GEP1]], [[GEP2]]
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %gep1 = getelementptr nuw i32, ptr %foo, i64 %i
+ %gep2 = getelementptr nusw i8, ptr %foo, i64 %j
+ %cmp = icmp ult ptr %gep1, %gep2
+ ret i1 %cmp
+}
+
define i1 @test_gep_ult_no_inbounds(ptr %foo, i64 %i, i64 %j) {
; CHECK-LABEL: @test_gep_ult_no_inbounds(
; CHECK-NEXT: [[GEP1:%.*]] = getelementptr i32, ptr [[FOO:%.*]], i64 [[I:%.*]]
``````````
</details>
https://github.com/llvm/llvm-project/pull/118472
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