As reported by @regehr (thanks!) on twitter (https://twitter.com/johnregehr/status/1057681496255815686),
we (me) has completely forgot about the binary assignment operator.
In AST, it isn't represented as separate ImplicitCastExpr's,
but as a single CompoundAssignOperator, that does all the casts internally.
Which means, out of these two, only the first one is diagnosed:
auto foo() {
unsigned char c = 255;
c = c + 1;
return c;
}
auto bar() {
unsigned char c = 255;
c += 1;
return c;
}This patch does handle the CompoundAssignOperator:
int main() {
unsigned char c = 255;
c += 1;
return c;
}$ ./bin/clang -g -fsanitize=integer /tmp/test.c && ./a.out /tmp/test.c:3:5: runtime error: implicit conversion from type 'int' of value 256 (32-bit, signed) to type 'unsigned char' changed the value to 0 (8-bit, unsigned) #0 0x2392b8 in main /tmp/test.c:3:5 #1 0x7fec4a612b16 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x22b16) #2 0x214029 in _start (/build/llvm-build-GCC-release/a.out+0x214029)