From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id A692E3858D39; Tue,  7 Mar 2023 12:57:37 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org A692E3858D39
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1678193857;
	bh=Ud1s3j5Ae3tzs6cZoa5epAtj9/aOgX6jncbjZQT15Q0=;
	h=From:To:Subject:Date:From;
	b=A9MIYJPMM9lwGvvtz/YZPH6vlvjc5l3j3A3X+16T+zJ7OwsunX3G4dFd6tTA/Foxw
	 3wPMSytj514EaaAXEchiMcUnXoxDmtwrLfaR9Gjho1E+R567zBbJENasS0fCT6jXKH
	 fzduf0dqVCdq3um00eUPGAxFb6Ql2jTqRH4kBxOc=
From: "ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/109052] New: Unnecessary reload with
 -mfpmath=both
Date: Tue, 07 Mar 2023 12:57:37 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: ubizjak at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-109052-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109052

            Bug ID: 109052
           Summary: Unnecessary reload with -mfpmath=3Dboth
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ubizjak at gmail dot com
  Target Milestone: ---

Following testcase:

--cut here--
double foo (double a)
{
  double tmp =3D a;
  asm ("" : "+t" (tmp));
  return a * tmp;
}
--cut here--

compiles with -O2 -mfpmath=3Dboth -msse2 to:

foo:
        movsd   %xmm0, -8(%rsp)
        fldl    -8(%rsp)
        fstpl   -8(%rsp)
-->     movsd   -8(%rsp), %xmm1
        mulsd   %xmm1, %xmm0
        ret

There is no need to reload from -8(%rsp) to %xmm1, mulsd accepts memory
operands. Optimal code would be:

foo:
        movsd   %xmm0, -8(%rsp)
        fldl    -8(%rsp)
        fstpl   -8(%rsp)
        mulsd   -8(%rsp), %xmm0
        ret

Please note that with -mfpmath=3Dsse, expected code is generated.

The insns pattern is defined in i386.md:

(define_insn "*fop_<mode>_comm"
  [(set (match_operand:MODEF 0 "register_operand" "=3Df,x,v")
        (match_operator:MODEF 3 "binary_fp_operator"
          [(match_operand:MODEF 1 "nonimmediate_operand" "%0,0,v")
           (match_operand:MODEF 2 "nonimmediate_operand" "fm,xm,vm")]))]
  "((SSE_FLOAT_MODE_P (<MODE>mode) && TARGET_SSE_MATH)
    || (TARGET_80387 && X87_ENABLE_ARITH (<MODE>mode)))
   && COMMUTATIVE_ARITH_P (operands[3])
   && !(MEM_P (operands[1]) && MEM_P (operands[2]))"
  "* return output_387_binary_op (insn, operands);"
  [(set (attr "type")
        (if_then_else (eq_attr "alternative" "1,2")
           (if_then_else (match_operand:MODEF 3 "mult_operator")
              (const_string "ssemul")
              (const_string "sseadd"))
           (if_then_else (match_operand:MODEF 3 "mult_operator")
              (const_string "fmul")
              (const_string "fop"))))
   (set_attr "isa" "*,noavx,avx")
   (set_attr "prefix" "orig,orig,vex")
   (set_attr "mode" "<MODE>")
   (set (attr "enabled")
     (if_then_else
       (match_test ("SSE_FLOAT_MODE_P (<MODE>mode) && TARGET_SSE_MATH"))
       (if_then_else
         (eq_attr "alternative" "0")
         (symbol_ref "TARGET_MIX_SSE_I387
                      && X87_ENABLE_ARITH (<MODE>mode)")
         (const_string "*"))
       (if_then_else
         (eq_attr "alternative" "0")
         (symbol_ref "true")
         (symbol_ref "false"))))])

The difference between -mfpmath=3Dboth and -mfpmath=3Dsse is in alternative=
 0,
which is enabled with -mfpmath=3Dboth and disabled with -mpmath=3Dsse. Usin=
g -mavx
instead of -msse2 with -mfpmath=3Dboth does not solve the problem.=