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Re: [PATCH] Change bb-reorder.c to use succ block frequency
- From: David Edelsohn <dje at watson dot ibm dot com>
- To: Richard Henderson <rth at redhat dot com>, Pat Haugen <pthaugen at us dot ibm dot com>, gcc-patches at gcc dot gnu dot org
- Date: Mon, 13 Jun 2005 16:06:29 -0400
- Subject: Re: [PATCH] Change bb-reorder.c to use succ block frequency
- References: <OFB50C7BED.C994B1ED-ON8625701F.0067F054-8625701F.0068F77A@us.ibm.com> <20050613195854.GB9939@redhat.com>
>>>>> Richard Henderson writes:
Richard> Why? It seems to me that edge frequency is what's going to matter
Richard> to the cpu when considering the branch. Particularly for cpus that
Richard> don't have horrendously sophisticated branch predictors.
From Pat's original message:
"Since edge frequency is based off the source block's frequency (src blk
freq * edge prob), this means the code in better_edge_p() which compares
frequencies if edge probabilities are equivalent is useless (if
probabilities are equivalent then the edge frequencies will also be
equivalent since they're based off the same block frequency)."
http://gcc.gnu.org/ml/gcc/2005-04/msg00638.html
David