[Bug target/95218] [11 Regression] FAIL: gcc.target/i386/fma_run_double_1.c execution test since r11-455-g94f687bd9ae37ece

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95218

--- Comment #10 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 20 May 2020, ubizjak at gmail dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95218
> 
> Uroš Bizjak <ubizjak at gmail dot com> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>                  CC|                            |law at gcc dot gnu.org,
>                    |                            |rsandifo at gcc dot gnu.org
> 
> --- Comment #9 from Uroš Bizjak <ubizjak at gmail dot com> ---
> (In reply to Uroš Bizjak from comment #7)
> > Ooh, yes :(
> > 
> > '(use X)'
> >      Represents the use of the value of X.  It indicates that the value
> >      in X at this point in the program is needed, even though it may not
> >      be apparent why this is so.  Therefore, the compiler will not
> >      attempt to delete previous instructions whose only effect is to
> >      store a value in X.  X must be a 'reg' expression.
> > 
> > Partial revert is in works.
> 
> Actually, no. The above applies to single (use ...) RTX, not (use ...) as part
> of a parallel. There are plenty of uses of memory_operands in i386.md:
> 
> (define_insn "fix_truncdi_i387"
>   [(set (match_operand:DI 0 "nonimmediate_operand" "=m")
>         (fix:DI (match_operand 1 "register_operand" "f")))
>    (use (match_operand:HI 2 "memory_operand" "m"))
>    (use (match_operand:HI 3 "memory_operand" "m"))
>    (clobber (match_scratch:XF 4 "=&f"))]
> 
> Let's ask experts.

The question is what should the (use ...) do?  Allow the splitter
to use its contents?  I guess that's reasonable interpretation
though I thought (use ...) apply only to register liveness computation
and not to memory.  But what do I know about RTL ;)