Re: [PATCH] move superblock formation to Tree-SSA

[Robert Kidd <rkidd at crhc dot uiuc dot edu>]

Here is a revised version of the patch to move Superblock formation  
to Tree-SSA.  I believe this addresses most of the feedback from the  
earlier version.

This patch moves the Superblock formation pass to after the first DCE  
pass in Tree-SSA.  I tested versions running Superblock formation  
after build_ssa, after ccp, and after dce.  Forming Superblocks after  
ccp performed better than after build_ssa, and forming them after dce  
performed better than that.  This patch improves performance 1-2%  
over the earlier version.  Full SPEC results are at http:// 
www.crhc.uiuc.edu/~rkidd/spec-tracer.html.

Moving Superblock formation to the Tree-SSA level does not degrade  
the run time of GCC.  I collected the output of -ftime-report for a  
SPEC2000 run on IA64 with and without the patch.  When doing  
profiling, the mean run time of the patched GCC is 0.99 times that of  
the standard.  When forming Superblocks without profile feedback, the  
run time is 0.97 times stock.  I considered only run times longer  
than five seconds in these calculations.

As for the performance of the compiled program, the mean difference  
in SPEC performance is in the noise.  There's a slight decrease for  
SPECint when profiling, and a slight increase in SPECfp without  
profiling.  mcf, swim, art, and lucas all improve by about 5% when  
we're not doing profiling, which is surprising.  The decrease in  
performance for twolf is still there.  I'm looking into the degraded  
benchmarks.  SPEC results are available at http://www.crhc.uiuc.edu/ 
~rkidd/spec-20070212-web.html.

This version of the patch still deletes dominance info after creating  
Superblocks.  I'm working on a version that updates dominators on the  
fly, but I still hit some ICEs with that version.

This patch bootstraps on x86_64 and ia64.

Thanks
Robert Kidd
rkidd@crhc.uiuc.edu

2006-02-21  Robert Kidd  <rkidd@crhc.uiuc.edu>

	* bb-reorder.c (rest_of_handler_reorder_blocks): Removed call to
	RTL level tracer pass.
	* passes.c (init_optimization_passes): Move pass_tracer from
	after pass_rtl_ifcvt to after pass_dce.
	* tracer.c: Update copyright.
	(layout_superblocks): Remove function.
	(mark_bb_seen): New.
	(bb_seen_p): New.
	(count_insns): Change to estimate instructions in a Tree-SSA
	statement.
	(find_trace): Use bb_seen_p.
	(tail_duplicate): Use bb_seen_p.  Call add_phi_args_after_copy
	after duplicate_block.
	(tracer): Change prototype to match that of a pass execute
	callback.
	(gate_tracer): Rename from gate_handle_tracer.
	(rest_of_handle_tracer): Remove function.
	* rtl.h: Remove prototype for tracer.
	* testsuite/gcc.dg/tree-prof/tracer-1.c: New.

Attachment: superblock-1.patch.txt
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