[clang][sema] Ignore xor-used-as-pow if both sides are macros

This happens in codebases a lot, which use xor where both sides are
macros. Using xor in that case is not the common error-prone 2^6 code
that the warning was introduced for.

Don't diagnose such a use of xor.

Differential Revision: https://reviews.llvm.org/D97445

clang/lib/Sema/SemaExpr.cpp

@@ -12102,6 +12102,11 @@ static void diagnoseXorMisusedAsPow(Sema &S, const ExprResult &XorLHS,
   if (Loc.isMacroID())
     return;
 
+  // Do not diagnose if both LHS and RHS are macros.
+  if (XorLHS.get()->getExprLoc().isMacroID() &&
+      XorRHS.get()->getExprLoc().isMacroID())
+    return;
+
   bool Negative = false;
   bool ExplicitPlus = false;
   const auto *LHSInt = dyn_cast<IntegerLiteral>(XorLHS.get());

clang/test/SemaCXX/warn-xor-as-pow.cpp

@@ -65,6 +65,7 @@ void test(unsigned a, unsigned b) {
 
   res = 2 ^ 0x4;
   res = 2 ^ 04;
+  res = TWO ^ TEN;
   res = 0x2 ^ 10;
   res = 0X2 ^ 10;
   res = 02 ^ 10;