Created attachment 13602 [details]
example code

the following code when built with clang 3.5.0 with -O1 or above is compiled incorrectly:

#include <stdio.h>

union u {
   size_t _refptr;

   void setPtr(int* refptr, bool readonly = false) {
      _refptr = (size_t)refptr;
      if (readonly)
         _refptr |= 1;
   }

   int* getPtr() const {
      // the line below is compiled incorrectly with clang++ 3.5.0 -O1 or above
      return (int*)((_refptr & 1L) ? (_refptr ^ 1L) : _refptr);
   }
};

int main(int argc, char *argv[]) {
   u u;
   int i = 100;
   
   u.setPtr(&i);
   printf("i: %p p(i): %p: %s\n", &i, u.getPtr(), &i == u.getPtr() ? "OK" : "ERROR");

   return 0;
}

-- example output is:
i: 0x7fff6adf3dac p(i): 0x7fff6adf3dad: ERROR

basically the conditional operator is evaluated with the opposite arguments according to its boolean operand expression in this case.

I tried some other simple cases and it was OK - no clue why this is happening, but in my case it's a big bug (I store values in the low bits of some pointers using this trick in some cases to optimize memory usage).

Note that compiling without optimizations results in correct code generation.  Maybe there's something awry with the optimizer with this case.