Hello again,

Thanks for both replies, they'll be useful to me. I wanted to disable
conditional execution for research purposes.


Fernando A. Endo, Post-doc

INRIA Rennes-Bretagne Atlantique

2016-09-20 20:21 GMT+02:00 Jim Wilson <jim.wil...@linaro.org>:

> On Tue, Sep 20, 2016 at 8:07 AM, Fernando Endo <fernando.en...@gmail.com>
> wrote:
> > I'm using Linaro GCC 4.9-2015.01-3 for AArch64, and trying to disable the
> > generation of guarded instructions. More specifically, I'd like not to
> see
> > instructions such as 'cset', 'csinc', 'ccmp', 'fccmp', etc.
> There are a lot of different optimization passes that can generate
> these instructions, and probably not all of them can be disabled via
> options.  A better approach would be to disable the patterns that
> generate the conditional move instructions.  The compiler should still
> work without them.  In the gcc/config/aarch64/aarch64.md file, you
> want to disable all of the patterns after the comment
> ;; -------------------------------------------------------------------
> ;; Store-flag and conditional select insns
> ;; -------------------------------------------------------------------
> and before the Logical operations comment.  You can disable a pattern
> by modifying the first set of quotes from "" to "0", or if there is
> already code there, change it to "0 && ..." where ... is the original
> code.  Or alternatively, you can just delete all of the patterns.  I
> see that there is one crc pattern mixed in among the csel patterns,
> which is an odd place for it.  That one should not be touched, though
> it is only used if the code being compiled calls one of the crc
> builtin functions, which is uncommon.
> For the conditional compare instructions, this is a little more
> complicated.  You need to disable or delete the cbranchcc4,
> ccmp<mode>, fccmp<mode>, and fccmpe<mode> patterns in the aarch64.md
> file.  And you also need to delete the #undef and #define in aarch64.c
> If you want a more useful patch, you can add a compiler option, and
> then make all of the patterns conditional on the compiler option, so
> that they can be turned off and on via the command line instead of
> needing two different compilers.
> I haven't tried this myself, so there could be some issues that I
> overlooked.  I would expect this to work though.
> Jim
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