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Re: [PATCH 5/9] regrename: Don't run if function was separately shrink-wrapped
On Wed, Sep 14, 2016 at 01:35:57PM -0600, Jeff Law wrote:
> On 09/14/2016 01:03 PM, Segher Boessenkool wrote:
> >
> >(There is no return insn at those exits; these are exits *without*
> >successor block, not the exit block).
> Hmm, I thought these were return blocks, but you're saying they're
> no-return blocks? I missed that.
>
> In that case, aren't the restores dead because no callers can observe
> their value changing unexpectedly?
Yes, but DCE can not remove the insns because dwarf2cfi would throw a
fit (and for good reason). That is why adding all these USEs makes
the DCE patch unnecessary (that patch simply disallows deleting insns
with a REG_CFA_RESTORE note, much simpler than all that USE surgery,
and perfectly correct and pretty much the best we can do).
The problem is that regrename decides to rename a (volatile) register to
some non-volatile register that is *not* separately shrink-wrapped (and
not actually dead there). Why would it do that, why would it not do that
if not separately shrink-wrapping at all?
(I did run this with checking=yes,rtl btw, it is not simple corruption).
Segher