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From: Eric Botcazou <ebotcazou@adacore.com>
To: Alexandre Oliva <aoliva@redhat.com>
Subject: Re: SRA bit-field optimization
Date: Sun, 07 Oct 2007 09:01:00 -0000
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Cc: gcc-patches@gcc.gnu.org,  Roman Zippel <zippel@linux-m68k.org>,  Bernd Schmidt <bernds_cb1@t-online.de>,  Diego Novillo <dnovillo@acm.org>,  Daniel Berlin <dberlin@dberlin.org>,  Andrew Pinski <pinskia@gmail.com>
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> What pessimization?

The complex calculation now introduced by SRA:

  SR.135_147 = SR.128_80 & 4294967295;
  SR.138_83 = SR.130_124 >> 32;
  SR.136_141 = (p__sm___XDLU_1__10) SR.138_83;
  SR.139_140 = (UNSIGNED_64) SR.136_141;
  SR.140_138 = SR.139_140 << 32;
  SR.128_92 = SR.135_147 | SR.140_138;
  SR.141_201 = SR.128_92 & 0x0ffffffff00000000;
  SR.142_200 = (p__sm___XDLU_1__10) SR.130_124;
  SR.144_199 = (UNSIGNED_64) SR.142_200;
  SR.128_137 = SR.141_201 | SR.144_199;

It turns out that SR.128_137 is dead so the whole stuff is eliminated by the 
first subsequent DCE pass, but I'm worried that it might not always be so.

I confirm that the verification failure of c37213b is fixed by the patch you 
posted in your previous message, thanks!

-- 
Eric Botcazou