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Re: Notes toward re-implementing EH in gimple
- From: Richard Henderson <rth at redhat dot com>
- To: Jan Hubicka <hubicka at ucw dot cz>
- Cc: gcc at gcc dot gnu dot org
- Date: Fri, 07 Aug 2009 12:22:43 -0700
- Subject: Re: Notes toward re-implementing EH in gimple
- References: <4A79EA5A.6030506@redhat.com> <20090806154859.GC23386@atrey.karlin.mff.cuni.cz> <4A7B00D0.2090509@redhat.com> <4A7B307F.8060108@redhat.com>
On 08/06/2009 12:35 PM, Richard Henderson wrote:
{ exc_ptr, filter } = EH_LANDING_PAD;
Placeholder for the landing-pad rtl. Has 2 outputs
for both the exception pointer and the filter.
I'm going to drop this construct. Instead, I'm going to mark
the label, and have the landing pad code be emitted as it
currently is by the rtl. This will prevent any problems with
the landing pad code being moved away from the start of the
block.
I'm going to adjust the rtl code so that it generates different
pseudos for exc_ptr and filter for each region. These will be
accessible from gimple with the EXC_PTR_EXPR and FILTER_EXPR
tree codes.
EXC_PTR_EXPR and FILTER_EXPR will be expanded to take the EH
region number as a parameter. Since they no longer need to be
saved and restored, they will no longer be gimple lvalues.
In gimple, the landing pad will be generated as
L.N:
exc_ptr.1 = EXC_PTR_EXPR (N);
filter.1 = FILTER_EXPR (N);
ie, copied into normal variables for use. These can be moved
about, or deleted, as the optimizer desires.
All of this seems much cleaner than what I initially imagined.
r~