> -----邮件原件-----
> 发件人: Jeff Law <jeffreya...@gmail.com>
> 发送时间: 2021年3月20日 23:42
> 收件人: yunqiang...@cipunited.com; gcc-patches@gcc.gnu.org
> 抄送: ma...@orcam.me.uk; l...@redhat.com; d...@debian.org;
> s...@debian.org; jiaxun.y...@flygoat.com
> 主题: Re: 回复: [PATCH v4 1/2] MIPS: Not trigger error for pre-R6 and
> -mcompact-branches=always
>
>
> On 3/3/2021 8:33 PM, yunqiang...@cipunited.com wrote:
> >> On 2/23/21 3:14 AM, YunQiang Su wrote:
> >>> For MIPSr6, we may wish to use compact-branches only.
> >>> Currently, we have to use `always' option, while it is mark as
> >>> conflict with pre-R6.
> >>> cc1: error: unsupported combination: ‘mips32r2’
> >>> -mcompact-branches=always Just ignore -mcompact-branches=always
> for
> >> pre-R6.
> >>> This patch also defines
> >>> __mips_compact_branches_never
> >>> __mips_compact_branches_always
> >>> __mips_compact_branches_optimal predefined macros
> >>>
> >>> gcc/ChangeLog:
> >>> * config/mips/mips.c (mips_option_override):
> >>> * config/mips/mips.h (TARGET_RTP_PIC): not trigger error for
> >>> compact-branches=always for pre-R6.
> >>> (TARGET_CB_NEVER): Likewise.
> >>> (TARGET_CB_ALWAYS): Likewise.
> >>> (struct mips_cpu_info): define macros for compact branch policy.
> >>> * doc/invoke.texi: Document "always" with pre-R6.
> >>>
> >>> gcc/testsuite/ChangeLog:
> >>> * gcc.target/mips/compact-branches-1.c: add isa_rev>=6.
> >>> * gcc.target/mips/mips.exp: don't add -mipsXXr6 option for
> >>> -mcompact-branches=always. It is usable for pre-R6 now.
> >>> * gcc.target/mips/compact-branches-8.c: New test.
> >>> * gcc.target/mips/compact-branches-9.c: New test.
> >> So I think Maciej's comment was that you simply shouldn't be using
> >> -mcompact-branches=always at mips32r2 (or anything pre-r6) together.
> >>
> >> I think what you're trying to do here is set up a scenario where
> >> you're defaulting to mips32r6 and compact-branches, but not error if
> >> something specifies -mcpu=mips32r2 or something similar, right?
> >>
> > Yes. If we introduce the build time option, and configure gcc with
> > always, then gcc will always try to Pass -mconpact-branches=always to cc1,
> even we use something like:
> > mipsisa32r6el-linux-gnu-gcc -mips32r2 -c xx.c It may break
> > something.
>
> So would it be possible to make the mips32rX (for X <6) option also turn off
Yes. It is possible, while it may introduce lots of complexity to the code.
> compact-branches? Maciej, is that less problematical from your
> standpoint? Or is this just ultimately a bad idea from start to finish?
>
>
> Jeff
