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Ping: [PATCH] Enable bbro for -Os



> -----Original Message-----
> From: [mailto:gcc-patches-
>] On Behalf Of Zhenqiang Chen
> Sent: Tuesday, August 14, 2012 2:50 PM
> To:
> Subject: [PATCH] Enable bbro for -Os
> Hi,
> Basic block reordering is disabled for -Os from gcc 4.7 since the pass
will lead
> to big code size regression. But benchmarks logs also show there are lots
> regression due to poor code layout compared with 4.6.
> The patch is to enable bbro for -Os. When optimizing for size, it
> * avoid duplicating block.
> * keep its original order if there is no chance to fall through.
> * ignore edge frequency and probability.
> * handle predecessor first if its index is smaller to break long trace.
> * only connect Trace n with Trace n + 1 to reduce long jump.
> Here are the CSiBE code size benchmark results:
> * For ARM, code size reduces 0.21%.
> * For MIPS, code size reduces 0.25%.
> * For PPC, code size reduces 0.33%.
> * For X86, code size reduces 0.22%.
> The patch does not impact bbro when optimizing for speed. To verify it, I
> "objdump -d" all obj files from CSiBE (compiled with -O2) for
> ARM/MIPS/PPC/X86. The assembler with the patch is the same as it without
> the patch.
> No make check regression on ARM.
> Is it OK for trunk?
> Thanks!
> -Zhenqiang
> ChangeLog
> 2012-08-14  Zhenqiang Chen <>
> 	* bb-reorder.c (connect_better_edge_p): New added.
> 	(find_traces_1_round): When optimizing for size, ignore edge
> frequency
> 	and probability, and handle all in one round.
> 	(bb_to_key): Use bb->index as key for size.
> 	(better_edge_p): The smaller bb index is better for size.
> 	(connect_traces): Connect block n with block n + 1;
> 	connect trace m with trace m + 1 if falling through.
> 	(copy_bb_p): Avoid duplicating blocks.
> 	(gate_handle_reorder_blocks): Enable bbro when optimizing for -Os.

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