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From: anamax@earthlink.net To: gcc-gnats@gcc.gnu.org Subject: optimization/7270: Redundant compares not eliminated on x86. Date: Wed, 10 Jul 2002 22:46:00 -0000 [thread overview] Message-ID: <20020711053656.11031.qmail@sources.redhat.com> (raw) >Number: 7270 >Category: optimization >Synopsis: Redundant compares not eliminated on x86. >Confidential: no >Severity: serious >Priority: medium >Responsible: unassigned >State: open >Class: pessimizes-code >Submitter-Id: net >Arrival-Date: Wed Jul 10 22:46:00 PDT 2002 >Closed-Date: >Last-Modified: >Originator: Andy Freeman >Release: gcc 3.1 >Organization: >Environment: Redhat 7.3 >Description: A <= compare&branch followed by a == test on the same arguments uses a redundant compare for the == on x86. Using built-in specs. Configured with: ../gcc-3.1/configure Thread model: single gcc version 3.1 >How-To-Repeat: Look at the -O3 -S output for x86. Notice the two cmpls on either side of the "ja .L4". I believe that the second cmpl is unnecessary as the flags from the first should survive the "ja .L4". >Fix: Better value propagation. >Release-Note: >Audit-Trail: >Unformatted: ----gnatsweb-attachment---- Content-Type: application/octet-stream; name="ii.cc" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="ii.cc" dW5zaWduZWQgZm9vKHVuc2lnbmVkIGFbXSkgew0KICBmb3IoIHVuc2lnbmVkIGkgPSAwOyBpIDwg MTA7ICsraSApIHsNCiAgICBpZiggaSA8PSBhW2ldICkgew0KICAgICAgaWYoIGkgPT0gYVtpXSAp IHsNCglyZXR1cm4gOTsNCiAgICAgIH0gZWxzZSB7DQoJcmV0dXJuIDE1Ow0KICAgICAgfQ0KICAg IH0NCiAgfQ0KfQ0K
next reply other threads:[~2002-07-11 5:46 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-07-10 22:46 anamax [this message] 2003-05-13 18:56 Dara Hazeghi 2003-05-14 10:28 giovannibajo
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