[InstCombine] isKnownNonNegative should recognize b - a after a <= b
#145105
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@llvm/pr-subscribers-llvm-analysis Author: Ross Kirsling (rkirsling) ChangesFixes #142283. Full diff: https://github.com/llvm/llvm-project/pull/145105.diff 2 Files Affected:
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 73320b556f825..2025079f07572 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -278,7 +278,15 @@ static bool isKnownNonZero(const Value *V, const APInt &DemandedElts,
bool llvm::isKnownNonNegative(const Value *V, const SimplifyQuery &SQ,
unsigned Depth) {
- return computeKnownBits(V, SQ, Depth).isNonNegative();
+ if (computeKnownBits(V, SQ, Depth).isNonNegative())
+ return true;
+
+ Value *X, *Y;
+ if (match(V, m_NSWSub(m_Value(X), m_Value(Y))))
+ if (std::optional<bool> result = isImpliedByDomCondition(ICmpInst::ICMP_SLE, Y, X, SQ.CxtI, SQ.DL))
+ return *result;
+
+ return false;
}
bool llvm::isKnownPositive(const Value *V, const SimplifyQuery &SQ,
diff --git a/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
new file mode 100644
index 0000000000000..279a6de4125ed
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
@@ -0,0 +1,53 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+define void @test_as_arg(i8 %a, i8 %b) {
+; CHECK-LABEL: define void @test_as_arg(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[COND_END:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
+; CHECK-NEXT: [[CONV:%.*]] = zext nneg i8 [[SUB]] to i16
+; CHECK-NEXT: call void @subroutine(i16 [[CONV]])
+; CHECK-NEXT: br label %[[COND_END]]
+; CHECK: [[COND_END]]:
+; CHECK-NEXT: ret void
+;
+ %cmp = icmp sgt i8 %a, %b
+ br i1 %cmp, label %cond.end, label %cond.false
+
+cond.false:
+ %sub = sub nsw i8 %b, %a
+ %conv = sext i8 %sub to i16
+ call void @subroutine(i16 %conv)
+ br label %cond.end
+
+cond.end:
+ ret void
+}
+
+declare void @subroutine(i16)
+
+define i16 @test_as_retval(i8 %a, i8 %b) {
+; CHECK-LABEL: define i16 @test_as_retval(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[COND_TRUE:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_TRUE]]:
+; CHECK-NEXT: ret i16 0
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
+; CHECK-NEXT: [[CONV:%.*]] = zext nneg i8 [[SUB]] to i16
+; CHECK-NEXT: ret i16 [[CONV]]
+;
+ %cmp = icmp sgt i8 %a, %b
+ br i1 %cmp, label %cond.true, label %cond.false
+
+cond.true:
+ ret i16 0
+
+cond.false:
+ %sub = sub nsw i8 %b, %a
+ %conv = sext i8 %sub to i16
+ ret i16 %conv
+}
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@llvm/pr-subscribers-llvm-transforms Author: Ross Kirsling (rkirsling) ChangesFixes #142283. Full diff: https://github.com/llvm/llvm-project/pull/145105.diff 2 Files Affected:
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 73320b556f825..2025079f07572 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -278,7 +278,15 @@ static bool isKnownNonZero(const Value *V, const APInt &DemandedElts,
bool llvm::isKnownNonNegative(const Value *V, const SimplifyQuery &SQ,
unsigned Depth) {
- return computeKnownBits(V, SQ, Depth).isNonNegative();
+ if (computeKnownBits(V, SQ, Depth).isNonNegative())
+ return true;
+
+ Value *X, *Y;
+ if (match(V, m_NSWSub(m_Value(X), m_Value(Y))))
+ if (std::optional<bool> result = isImpliedByDomCondition(ICmpInst::ICMP_SLE, Y, X, SQ.CxtI, SQ.DL))
+ return *result;
+
+ return false;
}
bool llvm::isKnownPositive(const Value *V, const SimplifyQuery &SQ,
diff --git a/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
new file mode 100644
index 0000000000000..279a6de4125ed
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
@@ -0,0 +1,53 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+define void @test_as_arg(i8 %a, i8 %b) {
+; CHECK-LABEL: define void @test_as_arg(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[COND_END:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
+; CHECK-NEXT: [[CONV:%.*]] = zext nneg i8 [[SUB]] to i16
+; CHECK-NEXT: call void @subroutine(i16 [[CONV]])
+; CHECK-NEXT: br label %[[COND_END]]
+; CHECK: [[COND_END]]:
+; CHECK-NEXT: ret void
+;
+ %cmp = icmp sgt i8 %a, %b
+ br i1 %cmp, label %cond.end, label %cond.false
+
+cond.false:
+ %sub = sub nsw i8 %b, %a
+ %conv = sext i8 %sub to i16
+ call void @subroutine(i16 %conv)
+ br label %cond.end
+
+cond.end:
+ ret void
+}
+
+declare void @subroutine(i16)
+
+define i16 @test_as_retval(i8 %a, i8 %b) {
+; CHECK-LABEL: define i16 @test_as_retval(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[COND_TRUE:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_TRUE]]:
+; CHECK-NEXT: ret i16 0
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
+; CHECK-NEXT: [[CONV:%.*]] = zext nneg i8 [[SUB]] to i16
+; CHECK-NEXT: ret i16 [[CONV]]
+;
+ %cmp = icmp sgt i8 %a, %b
+ br i1 %cmp, label %cond.true, label %cond.false
+
+cond.true:
+ ret i16 0
+
+cond.false:
+ %sub = sub nsw i8 %b, %a
+ %conv = sext i8 %sub to i16
+ ret i16 %conv
+}
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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Hmm, the bot seems to be reporting an unrelated flaky failure. Also, mentioning @dtcxzyw since I don't have the ability to edit reviewers. |
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Fixes #142283.