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From: ottoni@ic.unicamp.br To: gcc-gnats@gcc.gnu.org Subject: optimization/4919: gcse inhibits loop optimization Date: Fri, 16 Nov 2001 23:39:00 -0000 [thread overview] Message-ID: <20011121142018.3034.qmail@sourceware.cygnus.com> (raw) >Number: 4919 >Category: optimization >Synopsis: gcse inhibits loop optimization >Confidential: no >Severity: serious >Priority: medium >Responsible: unassigned >State: open >Class: pessimizes-code >Submitter-Id: net >Arrival-Date: Wed Nov 21 06:26:00 PST 2001 >Closed-Date: >Last-Modified: >Originator: Guilherme Ottoni >Release: gcc version 3.1 20011029 (experimental) >Organization: >Environment: RedHat Linux 6.2 running on a PC (K6-II) >Description: Compiling with gcc -O2 the source attached, the loop optimizer fails to detect BIVs, and so misses the opportunity to apply all the loop optimizations. If you add the -no-gcse flag to the command line, the loop optimizer works properly. To check what the loop optimizer is doing, I'm looking at the debug file generated by -dL. >How-To-Repeat: Simply compile the source attached, with -O2, and with and without the -fno-gcse. Then look at the .loop debug files to check the problem. I'm using a dsp16xx target, but I think this problem will occur with any target, as it is before the backend. >Fix: Maybe enhancing the BIV detection method to get the BIVs in these cases. Another (dirty) solution would be to inhibit the GCSE to optimize the code in the LOOP_CONT. >Release-Note: >Audit-Trail: >Unformatted: ----gnatsweb-attachment---- Content-Type: application/octet-stream; name="cc2001.c" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="cc2001.c" bWFpbigpCnsKICBpbnQgIGksIGF2ZywgYVsxMDBdLCBlcnJvcjsKICBmb3IgKGk9MDsgaSA8IDkw OyBpKyspCiAgewogICAgaWYgKGklMikKICAgIHsgCiAgICAgIGF2ZyArPSBhW2krMV0gPDwgMjsK ICAgICAgYVtpKzJdID0gYXZnICogMzsKICAgIH0KICAgIGlmIChhdmcgPCBlcnJvcikKICAgICAg YXZnIC09IGFbaSsxXSAtIGVycm9yLzI7CiAgICBlbHNlCiAgICAgIGF2ZyAtPSBhW2krMl0gLSBl cnJvcjsKICB9Cn0KCg==
next reply other threads:[~2001-11-21 14:26 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2001-11-16 23:39 ottoni [this message] 2001-11-21 3:36 rth 2001-11-21 3:43 rth
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