From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 22941 invoked by alias); 28 Oct 2007 16:05:46 -0000 Received: (qmail 22893 invoked by uid 48); 28 Oct 2007 16:05:36 -0000 Date: Sun, 28 Oct 2007 16:05:00 -0000 Message-ID: <20071028160536.22892.qmail@sourceware.org> X-Bugzilla-Reason: CC References: Subject: [Bug regression/33928] 33% performance slowdown from 4.2.2 to 4.3.0 in floating-point code with computed gotos In-Reply-To: Reply-To: gcc-bugzilla@gcc.gnu.org To: gcc-bugs@gcc.gnu.org From: "lucier at math dot purdue dot edu" Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2007-10/txt/msg02494.txt.bz2 ------- Comment #7 from lucier at math dot purdue dot edu 2007-10-28 16:05 ------- time with -O2 instead of -O1: with 4.2.2: (time (direct-fft-recursive-4 a table)) 426 ms real time 426 ms cpu time (425 user, 1 system) no collections 64 bytes allocated no minor faults no major faults with 4.3.0: (time (direct-fft-recursive-4 a table)) 433 ms real time 433 ms cpu time (433 user, 0 system) no collections 64 bytes allocated no minor faults no major faults With -O1 -fno-ivopts: with 4.2.2: (time (direct-fft-recursive-4 a table)) 374 ms real time 374 ms cpu time (374 user, 0 system) no collections 64 bytes allocated no minor faults no major faults with 4.3.0: (time (direct-fft-recursive-4 a table)) 443 ms real time 443 ms cpu time (443 user, 0 system) no collections 64 bytes allocated 1 minor fault no major faults Why -fno-strict-aliasing: I don't need it for this particular routine, but in the rest of the file is part of a bignum library that accesses the bignum digits as arrays of either 8-, 32-, or 64-bit unsigned ints, and it hasn't been rewritten to use unions of arrays. (This is part of the runtime system of a Scheme implementation, and there are other places that just cast pointers to achieve low-level things.) -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33928