Re: [PATCH RFC] mips: add TARGET_ZERO_CALL_USED_REGS hook [PR104817, PR104820]

[Xi Ruoyao <xry111@mengyan1223.wang>]

On Fri, 2022-03-11 at 21:26 +0000, Qing Zhao wrote:
> Hi, Ruoyao,
> 
> (I might not be able to reply to this thread till next Wed due to a
> short vacation).
> 
> First, some comments on opening bugs against Gcc:
> 
> I took a look at the bug reports PR104817 and PR104820:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104820
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104817
> 
> I didn’t see a testing case and a script to repeat the error, so I
> cannot repeat the error at my side.

I've put the test case, but maybe you didn't see it because it is too
simple:

echo 'int t() {}' | /home/xry111/git-repos/gcc-test-mips/gcc/cc1 -nostdinc -fzero-call-used-regs=all

An empty function is enough to break -fzero-call-used-regs=all.  And if
you append -mips64r2 to the cc1 command line you'll get 104820.  I
enabled 4 existing tests for MIPS (reported "not work" on MIPS) in the
patch so I think it's unnecessary to add new test cases.

Richard: can we use MIPS_EPILOGUE_TEMP as a scratch register in the
sequence for zeroing the call-used registers, and then zero itself
(despite it's not in need_zeroed_hardregs)?
-- 
Xi Ruoyao <xry111@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University