[SCEV] Don't require NUW at first add when checking A+C1 < (A+C2)<nuw>

Relax the NUW requirements for isKnownPredicateViaNoOverflow, if the
second operand (Y) is a BinOp. The code only simplifies the condition if
C1 < C2, so if the BinOp is NUW, it doesn't matter whether the first
operand also has the NUW flag, as it cannot wrap if C1 < C2.

Author: fhahn

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -11228,8 +11228,7 @@ bool ScalarEvolution::isKnownPredicateViaNoOverflow(ICmpInst::Predicate Pred,
       XNonConstOp = X;
       XFlagsPresent = ExpectedFlags;
     }
-    if (!isa<SCEVConstant>(XConstOp) ||
-        (XFlagsPresent & ExpectedFlags) != ExpectedFlags)
+    if (!isa<SCEVConstant>(XConstOp))
       return false;
 
     if (!splitBinaryAdd(Y, YConstOp, YNonConstOp, YFlagsPresent)) {
@@ -11238,13 +11237,22 @@ bool ScalarEvolution::isKnownPredicateViaNoOverflow(ICmpInst::Predicate Pred,
       YFlagsPresent = ExpectedFlags;
     }
 
-    if (!isa<SCEVConstant>(YConstOp) ||
-        (YFlagsPresent & ExpectedFlags) != ExpectedFlags)
+    if (YNonConstOp != XNonConstOp)
       return false;
 
-    if (YNonConstOp != XNonConstOp)
+    if (!isa<SCEVConstant>(YConstOp))
       return false;
 
+    if (YNonConstOp != Y && ExpectedFlags == SCEV::FlagNUW) {
+      if ((YFlagsPresent & ExpectedFlags) != ExpectedFlags)
+        return false;
+    } else {
+      if ((XFlagsPresent & ExpectedFlags) != ExpectedFlags)
+        return false;
+      if ((YFlagsPresent & ExpectedFlags) != ExpectedFlags)
+        return false;
+    }
+
     OutC1 = cast<SCEVConstant>(XConstOp)->getAPInt();
     OutC2 = cast<SCEVConstant>(YConstOp)->getAPInt();