Re: [PATCH, GCC, stage1] Fallback to copy-prop if constant-prop not possible

[Jeff Law <law@redhat.com>]

On 04/16/2015 02:43 AM, Thomas Preud'homme wrote:
>> From: Jeff Law [mailto:law@redhat.com]
>> Sent: Monday, April 13, 2015 8:48 PM
>>
>> I know there were several followups between Steven and yourself.
>> With
>> stage1 now open, can you post a final version and do a final
>> bootstrap/test with it?
>
> Here is what came out of our discussion with Steven:
>
> The RTL cprop pass in GCC operates by doing a local constant/copy propagation
> first and then a global one. In the local one, if a constant cannot be propagated
> (eg. due to constraints of the destination instruction) a copy propagation is
> done instead. However, at the global level copy propagation is only tried if no
> constant can be propagated, ie. if a constant can be propagated but the
> constraints of the destination instruction forbids it, no copy propagation will be
> tried. This patch fixes this issue.
>
> ChangeLog entries are as follows:
>
> *** gcc/ChangeLog ***
>
> 2015-04-15  Thomas Preud'homme  <thomas.preudhomme@arm.com>
>                          Steven Bosscher <stevenb.gcc@gmail.com>
>
>          * cprop.c (cprop_reg_p): New.
>          (hash_scan_set): Use above function to check if register can be
>          propagated.
>          (find_avail_set): Return up to two sets, one whose source is
>          a register and one whose source is a constant.  Sets are returned in
>          an array passed as parameter rather than as a return value.
>          (cprop_insn): Use a do while loop rather than a goto.  Try each of the
>          sets returned by find_avail_set, starting with the one whose source is
>          a constant. Use cprop_reg_p to check if register can be propagated.
>          (do_local_cprop): Use cprop_reg_p to check if register can be
>          propagated.
>          (implicit_set_cond_p): Likewise.
>
> *** gcc/testsuite/ChangeLog ***
>
> 2015-04-15  Thomas Preud'homme  <thomas.preudhomme@arm.com>
>                          Steven Bosscher <stevenb.gcc@gmail.com>
>
>          * gcc.target/arm/pr64616.c: New file.
>
>
> And the patch is:
>
>
> diff --git a/gcc/cprop.c b/gcc/cprop.c
> index c9fb2fc..78541cf 100644
> --- a/gcc/cprop.c
> +++ b/gcc/cprop.c
> @@ -285,6 +285,15 @@ cprop_constant_p (const_rtx x)
>     return CONSTANT_P (x) && (GET_CODE (x) != CONST || shared_const_p (x));
>   }
>
> +/* Determine whether the rtx X should be treated as a register that can
> +   be propagated.  Any pseudo-register is fine.  */
> +
> +static bool
> +cprop_reg_p (const_rtx x)
> +{
> +  return REG_P (x) && !HARD_REGISTER_P (x);
> +}
How about instead this move to a more visible location (perhaps a macro 
in regs.h or an inline function).  Then as a followup, change the 
various places that have this sequence to use that common definition 
that exist outside of cprop.c.

> @@ -1191,7 +1192,7 @@ do_local_cprop (rtx x, rtx_insn *insn)
>     /* Rule out USE instructions and ASM statements as we don't want to
>        change the hard registers mentioned.  */
>     if (REG_P (x)
> -      && (REGNO (x) >= FIRST_PSEUDO_REGISTER
> +      && (cprop_reg_p (x)
>             || (GET_CODE (PATTERN (insn)) != USE
>   	      && asm_noperands (PATTERN (insn)) < 0)))
Isn't the REG_P test now redundant?

OK for the trunk with those changes.

jeff