Anton Blanchard wrote:
>I changed the code a bit so that get_cpu() is now inline - this
>represents our situation better. I think it is valid for gcc to cache
>get_cpu across a function call in the below example because it knows
>that get_cpu does not refer to any global variables.
>
You are right: it seems that gcc internally decides if an inline
function is const or pure.
static inline int get_TR(void)
{
int reg;
__asm__ (
"rep; nop;\n\t"
"xor %0,%0\n\t"
: "=r" (reg));
return ret;
}
is always optimized as if get_TR is a function with __attribute__((const)).
Ben, is it intentional that get_TR is _not_ marked as inline? Your
version produces explicit function calls with -O2, and incorrect code
with -O99 (gcc decides to inline get_TR even without an inline
directive, and then optimizes away the calls after schedule.)
It seems that Anton's version generates the best code.
I've tested the attached version with egcs-1.1.2, gcc-2.96-98 and
gcc3-3.0.1-3, with -O0, -O2 and -O99.
--
Manfred
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This archive was generated by hypermail 2b29 : Thu Nov 15 2001 - 21:00:26 EST