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Re: Question about make_extraction() in combine.c
- From: Segher Boessenkool <segher at kernel dot crashing dot org>
- To: Michael Eager <eager at eagerm dot com>
- Cc: gcc-help at gcc dot gnu dot org
- Date: Fri, 16 Nov 2018 16:50:23 -0600
- Subject: Re: Question about make_extraction() in combine.c
- References: <71017eb1-ed7e-ec1d-1b4e-c1f973b08489@eagerm.com>
Hi!
On Wed, Nov 14, 2018 at 11:22:58AM -0800, Michael Eager wrote:
> The (mem:SI) is converted to (mem:QI).
>
> The return from make_extract() is
> (zero_extract:SI (mem:QI (reg/v/f:SI 50 [ gp ]))
> (const_int 1 [0x1])
> (const_int 2 [0x2]))
>
> The target has an instruction pattern for zero_extract, but it matches
> SI values, not QI. So the instruction which implements a test of a bit
> flag is never generated.
The RTL documentation says:
If @var{loc} is in memory, its mode must be a single-byte integer mode.
But obviously various ports use other modes, too. I wonder if that ever
worked well.
Segher