Skip both character pointers and void pointers when diagnosing bad

argument types for mem{set,cpy,move}. Character pointers, much like void
pointers, often point to generic "memory", so trying to check whether
they match the type of the argument to 'sizeof' (or other checks) is
unproductive and often results in false positives.

Nico, please review; does this miss any of the bugs you were trying to
find with this warning? The array test case you had should be caught by
the array-specific sizeof warning I think.

llvm-svn: 133136

clang/lib/Sema/SemaChecking.cpp

@@ -1866,7 +1866,9 @@ void Sema::CheckMemsetcpymoveArguments(const CallExpr *Call,
     if (const PointerType *DestPtrTy = DestTy->getAs<PointerType>()) {
       QualType PointeeTy = DestPtrTy->getPointeeType();
 
-      if (PointeeTy->isVoidType())
+      // Don't warn about void pointers or char pointers as both are often used
+      // for directly representing memory, regardless of its underlying type.
+      if (PointeeTy->isVoidType() || PointeeTy->isCharType())
         continue;
 
       // Catch "memset(p, 0, sizeof(p))" -- needs to be sizeof(*p).

clang/test/SemaCXX/warn-memset-bad-sizeof.cpp

@@ -23,10 +23,11 @@ inline Dest bit_cast(const Source& source) {
 }
 
 // http://www.lysator.liu.se/c/c-faq/c-2.html#2-6
-void f(char fake_array[8], Mat m, const Foo& const_foo) {
+void f(Mat m, const Foo& const_foo) {
   S s;
   S* ps = &s;
   PS ps2 = &s;
+  char c = 42;
   char arr[5];
   char* parr[5];
   Foo foo;
@@ -42,8 +43,6 @@ void f(char fake_array[8], Mat m, const Foo& const_foo) {
       // expected-warning {{the argument to sizeof is pointer type 'typeof (ps2)' (aka 'S *'), expected 'S' to match first argument to 'memset'}}
   memset(ps2, 0, sizeof(PS));  // \
       // expected-warning {{the argument to sizeof is pointer type 'PS' (aka 'S *'), expected 'S' to match first argument to 'memset'}}
-  memset(fake_array, 0, sizeof(fake_array));  // \
-      // expected-warning {{the argument to sizeof is pointer type 'char *', expected 'char' to match first argument to 'memset'}}
 
   memcpy(&s, 0, sizeof(&s));  // \
       // expected-warning {{the argument to sizeof is pointer type 'S *', expected 'S' to match first argument to 'memcpy'}}
@@ -69,6 +68,8 @@ void f(char fake_array[8], Mat m, const Foo& const_foo) {
   memcpy(&foo, &const_foo, sizeof(Foo));
   memcpy((void*)&s, 0, sizeof(&s));
   memcpy(0, (void*)&s, sizeof(&s));
+  memcpy(&parr[3], &c, sizeof(&c));
+  memcpy((char*)&parr[3], &c, sizeof(&c));
 
   CFooRef cfoo = foo;
   memcpy(&foo, &cfoo, sizeof(Foo));