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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)."