* H. Peter Anvin (hpa@xxxxxxxxx) wrote:
> Mathieu Desnoyers wrote:
>> This epilogue should then be used on both branches of the condition,
>> like this :
>> if (unlikely(imv_cond(var))) {
>> imv_cond_end();
>> ...
>> } else {
>> imv_cond_end();
>> ...
>> }
>> Where imv_cond_end() would look like this :
>> +/*
>> + * Puts a test and branch make sure the %al register and ZF are not live
>> + * anymore.
>> + * All asm statements clobbers the flags, but add "cc" clobber just to be
>> sure.
>> + * Clobbers %al.
>> + */
>> +#define imv_cond_end() \
>> + do { \
>> + asm (".section __imv_cond_end,\"a\",@progbits\n\t" \
>> + _ASM_PTR "1f\n\t" \
>> + ".previous\n\t" \
>> + "1:\n\t" \
>> + : : : "a", "cc"); \
>> + } while (0)
>> +
>
> As far as this is concerned, all you accomplish here is that gcc, if it
> wants to re-use the %al value, will copy it into another register before
> doing your imv_conv_end().
>
Exactly, and by doing so, it will have to add instructions (mov, push..)
in the instruction pattern I am looking for and therefore I will detect
this and fall back on standard immediate values.
Mathieu
> -hpa
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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