[PATCH] Relax one gcc_assert in lra-eliminate for fixed register

[Jeff Law]

On 11/17/14 02:26, Jiong Wang wrote:
> as Pinski reported at
>
>    https://gcc.gnu.org/ml/gcc-patches/2014-11/msg01967.html
>
> the previosu LR free patch on AArch64 cause one gcc_assert in
> lra-elimination.c
>
> one of the problem is that gcc_assert is too strict and overkilled some
> valid cases.
>
> the purpose of that assert is described here
>
>    https://gcc.gnu.org/ml/gcc-patches/2013-12/msg00151.html
>
> and I checked the code, it's purpose is to prohibit the following scenario:
>
>    FP decided to be not required earlier, and then be required later.
>
> that assert prohibit above situation, because it will cause bad code
> generation. FP
> may be allocated earlier while because later it identified to be
> required as fixed purpose, then
> all those pseudo allocated to FP need to be spilled.
>
> so, this check will only make sense when that reg is not fixed itself.
>
> this patch relax that gcc_assert for fixed registers.
>
> the problem reported by Pinski fixed also, because FP of AArch64 is fixed.
>
> bootstrap ok on AArch64 and X86-64.
> no regression on X86-64.
> Pinskia's testcase passed on AArch64 on his code branch.
>
> ok for trunk?
>
> gcc/
>    * lra-eliminations.c (update_reg_eliminate): Relax gcc_assert for
> fixed registers.
OK for the trunk.  It'd be useful to have a test, but my understanding 
is you need Pinski's modifications to trigger the failure.  Correct?

Jeff