C question

[VLD/VMB]

The compiler is perfectly within its rights in making
	x = 5;
	x = x++;
result in x==5 sometimes and x==6 other times.  This
is one of the implementation-dependent aspects of the
C language, intended to allow better overall code
generation.  You should not write such source code.

If there is a
	movl	r11,r11
in your output, then you must not have invoked the C
optimizer (cc -O option).  To make code generation
easier and more reliable, the main compiler relies
on the optimizer to clean up such things.