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From: roger@eyesopen.com To: gcc-gnats@gcc.gnu.org Cc: roger@eyesopen.com Subject: optimization/6405: Loop-unrolling related performance regressions Date: Mon, 22 Apr 2002 07:56:00 -0000 [thread overview] Message-ID: <20020422144645.14270.qmail@sources.redhat.com> (raw) >Number: 6405 >Category: optimization >Synopsis: Loop-unrolling related performance regressions >Confidential: no >Severity: non-critical >Priority: medium >Responsible: unassigned >State: open >Class: pessimizes-code >Submitter-Id: net >Arrival-Date: Mon Apr 22 07:56:00 PDT 2002 >Closed-Date: >Last-Modified: >Originator: Roger Sayle <roger@eyesopen.com> >Release: gcc-3.1 branch and mainline 20020422 >Organization: >Environment: All platforms, but first observed on i686-pc-linux-gnu. >Description: See http://gcc.gnu.org/ml/gcc/2002-02/msg00307.html With the command line options "-O3 -funroll-loops", GCC 2.96 generates better code for the attached loop than GCC 3.1 (prerelease) or mainline. A correctness fix had the side effect that the compiler can no longer determine that this loop iterates a fix number of times. >How-To-Repeat: Compile the attached loop.c with "-O2 -funroll-all-loops" and inspect the assembly code generated. >Fix: >Release-Note: >Audit-Trail: >Unformatted: ----gnatsweb-attachment---- Content-Type: application/x-unknown-content-type-cfile; name="loop.c" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="loop.c" Y29uc3QgaW50IGZlYXR1cmVfdGltZXMgPSAyNTsKCmV4dGVybiB2b2lkIGZvbyh2b2lkKTsKCnZv aWQKdGVzdCAodm9pZCkKewogICBpbnQgaSA9IDE7CgogICBmb3IgKDs7KQogICAgIHsKICAgICAg IGZvbyAoKTsKICAgICAgIGkrKzsKICAgICAgIGlmIChpID4gZmVhdHVyZV90aW1lcykKICAgICAg ICAgYnJlYWs7CiAgICAgfQp9Cgo=
next reply other threads:[~2002-04-22 14:56 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-04-22 7:56 roger [this message] 2002-09-08 11:47 sayle
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