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Date: Mon, 05 Apr 2004 13:55:00 -0000
From: "uros at kss-loka dot si" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20040405135542.14851.uros@kss-loka.si>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug optimization/14851] New: suboptimal fp division
X-Bugzilla-Reason: CC
X-SW-Source: 2004-04/txt/msg00413.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

Floating point division in current CVS gcc expands x/x into (1/x)*x. This testcase:

double test(double x)
{
        return x/x;
}

is with gcc 3.5.0 20040405 (experimental) with -O2 -ffast-math compiled to:
test:
        pushl   %ebp
        movl    %esp, %ebp
        fldl    8(%ebp)
        fld1
        fdiv    %st(1), %st
        popl    %ebp
        fmulp   %st, %st(1)
        ret

And with gcc 3.2 20020903 (Red Hat Linux 8.0 3.2-7):
test:
        pushl   %ebp
        movl    %esp, %ebp
        fldl    8(%ebp)
        fdiv    %st(0), %st
        leave
        ret

-- 
           Summary: suboptimal fp division
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: uros at kss-loka dot si
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14851