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Date: Wed, 12 Jan 2005 13:34:00 -0000
From: "uros at kss-loka dot si" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20050112133406.19398.uros@kss-loka.si>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug target/19398] New: Non-optimal code with cvttss2si
X-Bugzilla-Reason: CC
X-SW-Source: 2005-01/txt/msg01508.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

The testcase:
int test (float a) {
        return (a*a);
}

produces non-optimal asm code, when compiled with '-O2 -msse -mfpmath=387':
test:
        pushl  %ebp
        movl   %esp, %ebp
        subl   $4, %esp
        flds   8(%ebp)
        fmul   %st(0), %st
        fstps  -4(%ebp)
(*)     movss  -4(%ebp), %xmm0
(*)     cvttss2si       %xmm0, %eax
        leave
        ret

A cvttss2si insn could use memory input operand, so movss to %xmm0 is not
needed. Following RTL sequence is generated in ._.23.greg:

(insn 31 11 32 0 (set (mem:SF (plus:SI (reg/f:SI 6 bp)
                (const_int -4 [0xfffffffc])) [0 S4 A8])
        (reg/v:SF 8 st [orig:59 a ] [59])) 61 {*movsf_1} (nil)
    (nil))

(insn 32 31 12 0 (set (reg:SF 21 xmm0)
        (mem:SF (plus:SI (reg/f:SI 6 bp)
                (const_int -4 [0xfffffffc])) [0 S4 A8])) 61 {*movsf_1} (nil)
    (nil))

(insn:HI 12 32 16 0 (set (reg:SI 0 ax [60])
        (fix:SI (reg:SF 21 xmm0))) 112 {fix_truncsfsi_sse}
(insn_list:REG_DEP_TRUE 11 (nil))
    (nil))

It looks like gcc does not take into account the fact that cvttss2si can use
memory input operand.

-- 
           Summary: Non-optimal code with cvttss2si
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: target
        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=19398