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

[Thomas Preud'homme]

Hi Steven,

> From: Steven Bosscher [mailto:stevenb.gcc@gmail.com]
> Sent: Friday, March 20, 2015 3:54 PM
> 
> 
> 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).

Ok.

> 
> 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 ;-)

I think it would be preferable to introduce PSEUDO_REG_P in rtl.h as this
seems like a common pattern enough [1]. It would be nice to have a
HARD_REG_P that would be cover the other common patterns
REG_P && < FIRST_PSEUDO_REGISTER and REG_P && HARD_REGISTER_P
but I can't come up with a good name (HARD_REGISTER_P is confusing
because it doesn't check if it's a register in the first place).

I noticed in do_local_cprop you replace >= FIRST_PSEUDO_REGISTER by
cprop_reg_p without removing the REG_P as well. In implicit_set_cond_p
there is a replacement of !REG_P || HARD_REGISTER_P by cprop_reg_p.
It seems to me it should rather be replaced by !cprop_reg_p. Otherwise it
looks ok.

[1] grep -R "REG_P .*&&.*>= FIRST_PSEUDO_REGISTER" . | wc -l returns 23

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

I'll try to launch a build and testsuite run with these 2 issues fixed before I
leave tonight and will report the result on Monday.

Best regards,

Thomas