Example of the optimiser recognising a pattern

I'm working with a microcontroller at the moment that has a single
instruction for clearing a bit in a byte.

I started off with the following line of code:

  x &= ~0x8u;    /* Clear the 4th bit */

But then I changed it to the following because I thought I might get
more efficient assembler out of it:

   x &= 0xF7u;   /* Clear the 4th bit */

Suprisingly, the compiler produced more efficient code for the latter,
presumably because it recognises the pattern of " x &= ~y" for
clearing a single bit.

Anyway just thought I'd give an example of someone winding up with
less efficient code when their aim was to make the code more
efficient :-D