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Re: [PING*2][PATCH] Extend mode-switching to support toggle (1/2)


On 13 May 2014 22:41, Oleg Endo <oleg.endo@t-online.de> wrote:

> Right.  I was thinking to add FPSCR.SZ mode switching to SH, in order to
> do float vector moves.  For that SZ and PR need to be switched both at
> the same time (only SH4A has both, fpchg and fschg).  So basically I'd
> add another mode entity, which would emit SZ mode changes in addition to
> the PR mode changes.  But then adjacent FPSCR-changing insns could be
> combined ... any idea/suggestion how to accomplish that?

If they are sufficiently adjacent, you can use a peephole2 pattern for this.

I see Cristian's patch addresses this in a different way - keeping size and
precision in the same entity, and emitting toggles as appropriate.

The problem get's a bit more interesting if you have some instruction patterns
that care about one setting but not the other.
Describing this exactly allows lazy code motion to be a bit more lazy, but OTOH
it can make it harder to combine mode switching instructions if you
still want to
do that.


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