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optimization/7270: Redundant compares not eliminated on x86.
- From: anamax at earthlink dot net
- To: gcc-gnats at gcc dot gnu dot org
- Date: 11 Jul 2002 05:36:56 -0000
- Subject: optimization/7270: Redundant compares not eliminated on x86.
- Reply-to: anamax at earthlink dot net
>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:
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