[Diagnostic] Warn if the size argument of memset is character literal

zero

Closing #55402

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D125521

clang/lib/Sema/SemaChecking.cpp

@@ -11200,7 +11200,10 @@ static void CheckMemaccessSize(Sema &S, unsigned BId, const CallExpr *Call) {
     Call->getArg(BId == Builtin::BImemset ? 2 : 1)->IgnoreImpCasts();
 
   auto isLiteralZero = [](const Expr *E) {
-    return isa<IntegerLiteral>(E) && cast<IntegerLiteral>(E)->getValue() == 0;
+    return (isa<IntegerLiteral>(E) &&
+            cast<IntegerLiteral>(E)->getValue() == 0) ||
+           (isa<CharacterLiteral>(E) &&
+            cast<CharacterLiteral>(E)->getValue() == 0);
   };
 
   // If we're memsetting or bzeroing 0 bytes, then this is likely an error.

clang/test/Sema/transpose-memset.c

@@ -11,8 +11,10 @@ int *ptr;
 int main(void) {
   memset(array, sizeof(array), 0); // expected-warning{{'size' argument to memset is '0'; did you mean to transpose the last two arguments?}} expected-note{{parenthesize the third argument to silence}}
   memset(array, sizeof(array), 0xff); // expected-warning{{setting buffer to a 'sizeof' expression; did you mean to transpose the last two arguments?}} expected-note{{cast the second argument to 'int' to silence}} expected-warning{{'memset' will always overflow; destination buffer has size 40, but size argument is 255}}
+  memset(array, sizeof(array), '\0'); // expected-warning{{'size' argument to memset is '0'; did you mean to transpose the last two arguments?}} expected-note{{parenthesize the third argument to silence}}
   memset(ptr, sizeof(ptr), 0); // expected-warning{{'size' argument to memset is '0'; did you mean to transpose the last two arguments?}} expected-note{{parenthesize the third argument to silence}}
   memset(ptr, sizeof(*ptr) * 10, 1); // expected-warning{{setting buffer to a 'sizeof' expression; did you mean to transpose the last two arguments?}} expected-note{{cast the second argument to 'int' to silence}}
+  memset(ptr, sizeof(ptr), '\0');    // expected-warning{{'size' argument to memset is '0'; did you mean to transpose the last two arguments?}} expected-note{{parenthesize the third argument to silence}}
   memset(ptr, 10 * sizeof(int *), 1); // expected-warning{{setting buffer to a 'sizeof' expression; did you mean to transpose the last two arguments?}} expected-note{{cast the second argument to 'int' to silence}}
   memset(ptr, 10 * sizeof(int *) + 10, 0xff); // expected-warning{{setting buffer to a 'sizeof' expression; did you mean to transpose the last two arguments?}} expected-note{{cast the second argument to 'int' to silence}}
   memset(ptr, sizeof(char) * sizeof(int *), 0xff); // expected-warning{{setting buffer to a 'sizeof' expression; did you mean to transpose the last two arguments?}} expected-note{{cast the second argument to 'int' to silence}}