[PATCH] PR34400 compile time in dataflow analysis

["Seongbae Park (박성배, 朴成培)" <seongbae dot park at gmail dot com>]

This patch implements another worklist based dataflow solver,
using double queue.
This reduces the -O2 compile time for two testcases attached in PR34400
from 1.27 and 15.03 seconds to 0.28 and 2.28 seconds respectively on my machine.
In particular, "df reaching defs" time changes
from 0.45 and 5.32 to 0.02 and 0.16.

The measurement on all dataflow solver invocation during cc1 build
shows that the new solver won't be triggered during bootstrap,
hence no bootstrap time impact is expected (I didn't do any
precise measurement of bootstrap times).

Bootstrapped and reg-tested on i686. OK for 4.3 ?
-- 
#pragma ident "Seongbae Park, compiler, http://seongbae.blogspot.com";

Attachment: pr34400-doublequeue-svn.diff
Description: Text document