[tree-ssa] Coalescing label blocks [patch]

[law@redhat.com]

In message <20030130175337.GA13405@tornado.toronto.redhat.com>, Diego Novillo w
rites:
 >On Thu, 30 Jan 2003, Jeff Law wrote:
 >
 >> Q. were you finding that the sequences of labels were typically normal
 >>    labels or case statement labels?  Just curious...
 >> 
 >Case labels are the overwhelming majority.  The worst case is
 >insn-extract.c and insn-attrtab.c with 696 and 654 case labels
 >coalesced respectively (not surprising).
OK.  That's basically what I expected.


 >We almost never find normal labels.  genrecog.c has 2 and
 >insn-recog.c has 5.
OK.


 >I found these numbers using the attached patch for
 >-fdump-tree-cfg-stats.
Great.

FYI, the coalescing patch is causing a testsuite regression

Running /portal/fall/virgin-tree-ssa/gcc/testsuite/gcc.misc-tests/bprob.exp ...
FAIL: gcc.misc-tests/bprob-1.c execution,    -O3 -DPERFTIME  -fprofile-arcs
FAIL: gcc.misc-tests/bprob-1.c execution,    -O3 -g -DPERFTIME  -fprofile-arcs


Both of these pass if I back out the coalescing patch.

 >>  >Interestingly enough
 >>  >most of the absolute time savings came from GCSE.  Before the
 >>  >patch, GCSE would take 36 secs, after the patch it takes 24 secs.
 >>  >It also improved scheduling2 by 6 seconds.  I wasn't expecting
 >>  >this.
 >> Definitely a surprise.  It seems to me that the RTL code would have
 >> coalesced those empty blocks, so it's a real surprise that this sped
 >> up gcse.  Any thoughts on how/why?
 >> 
 >Nope.  I can't see why this could happen.  Oh well, more food for
 >thought.
Definitely.  Very weird.

jeff