Address issue.

Author: rkirsling

llvm/lib/Analysis/ValueTracking.cpp

@@ -278,7 +278,16 @@ 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,

llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll

@@ -7,7 +7,7 @@ define void @test_as_arg(i8 %a, i8 %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:%.*]] = sext i8 [[SUB]] to i16
+; 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]]:
@@ -37,7 +37,7 @@ define i16 @test_as_retval(i8 %a, i8 %b) {
 ; CHECK-NEXT:    ret i16 0
 ; CHECK:       [[COND_FALSE]]:
 ; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
-; CHECK-NEXT:    [[CONV:%.*]] = sext i8 [[SUB]] to i16
+; CHECK-NEXT:    [[CONV:%.*]] = zext nneg i8 [[SUB]] to i16
 ; CHECK-NEXT:    ret i16 [[CONV]]
 ;
   %cmp = icmp sgt i8 %a, %b