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

[Steven Bosscher <stevenb dot gcc at gmail dot com>]

On Tue, Feb 17, 2015 at 3:51 AM, Thomas Preud'homme wrote:
>> > -      else if (REG_P (src)
>> > -              && REGNO (src) >= FIRST_PSEUDO_REGISTER
>> > -              && REGNO (src) != regno)
>> > -       {
>> > -         if (try_replace_reg (reg_used, src, insn))
>> > +         else if (src_reg && REG_P (src_reg)
>> > +                  && REGNO (src_reg) >= FIRST_PSEUDO_REGISTER
>> > +                  && REGNO (src_reg) != regno
>> > +                  && try_replace_reg (reg_used, src_reg, insn))
>>
>> Likewise for the REG_P and ">= FIRST_PSEUDO_REGISTER" tests here
>> (with
>> the equivalent and IMHO preferable HARD_REGISTER_P test in
>> find_avail_set()).
>
> I'm not sure I follow you here. First, it seems to me that the equivalent
> test is rather REG_P && !HARD_REGISTER_P since here it checks if it's
> a pseudo register.
>
> Then, do you mean the test can be simply removed because of the
> REG_P && !HARD_REGISTER_P in hash_scan_set () called indirectly by
> compute_hash_table () when called in one_cprop_pass () before any
> cprop_insn ()? Or do you mean I should move the check in
> find_avail_set ()?


What I meant, is that I believe the tests are already done in
hash_scan_set and should be redundant in cprop_insn (i.e. the test can
be replaced with gcc_[checking_]assert).

I've attached a patch with some changes to it: introduce cprop_reg_p()
to get rid of all the "REG_P && regno > FIRST_PSEUDO_REGISTER" tests.
I still have the cprop_constant_p and cprop_reg_p tests in cprop_insn
but this weekend I'll try with gcc_checking_asserts instead. Please
have a look at the patch and let me know if you like it (given it's
mostly yours I hope you do like it ;-)

Bootstrapped & tested on powerpc64-unknown-linux-gnu. In building all
of cc1, 35 extra copies are propagated with the patch.

Ciao!
Steven

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