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Re: PR63633: May middle-end come up width hard regs for insn expanders?

On 21/04/15 02:04 AM, Segher Boessenkool wrote:
On Tue, Apr 21, 2015 at 12:27:40AM +0200, Steven Bosscher wrote:
On Mon, Apr 20, 2015 at 10:11 PM, Vladimir Makarov wrote:
I might be wrong but I think you have a bloated code because you use
scratches.  I already told several times that usage of scratch is always a
bad idea.  It was a bad idea for an old RA and is still a bad idea for IRA.
The usage of scratches should be prohibited, probably we should write it
somewhere.  It is better to use just a regular pseudo instead.
Thanks Vladimir, I didn't know this.
Does this mean that, for example, extendsidi in would be
better if it did not use match_scratch?
The combiner can add or remove clobbers of scratches whenever needed,
but it cannot do that for clobbers of pseudos.

Yes, I think there are some pitfalls with scratches in other passes.

As for combiner, it is probably worth to consider processing clobbers of pseudos with *one* reference as scratches too. It might improve code for some cases although I am not sure about this.

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