[patch] Expand SJLJ exceptions as tablejump/casesi

[Steven Bosscher <stevenb dot gcc at gmail dot com>]

On Wed, Apr 18, 2012 at 2:44 PM, Richard Henderson wrote:
> On 04/18/2012 05:39 AM, Jan Hubicka wrote:
>> Well, if SJLJ lowering happens as gimple pass somewhere near the end of gimple
>> queue, this should not be problem at all. (and implementation would be cleaner)
>
> If you can find a clean way of separating sjlj expansion from dw2 expansion,
> please do.  But there's a lot of code shared between the two.  I see nothing
> wrong with always expanding via tablejump.

Hello,

This patch makes it so... well, almost anyway. With this patch, all
SJLJ exception dispatch tables with more than 5 case labels are are
expanded as a tablejump or a casesi.

With the existing code:
* a 1-case dispatch is expanded as a simple jump by code in except.c
* a >1-case dispatch is built as a GIMPLE_SWITCH and expanded via
expand_case as a decision tree if there are fewer than
case_values_threshold() cases, or a tablejump or casesi for everything
else

If my patch is OK, this changes to:
* a 1-case dispatch is expanded as a simple jump by code in except.c (unchanged)
* a >1-case dispatch is built as a VEC of CASE_LABEL nodes and
expanded via expand_sjlj_dispatch_table as a decrement-chain if there
are fewer than 5 cases, or a tablejump or casesi for everything else

Bootstrapped&tested on powerpc64-unknown-linux-gnu, and
multilib-bootstrapped on x86_64-unknown-linux-gnu with java enabled
and with --enable-sjlj-exceptions.
OK for trunk?

Ciao!
Steven

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