From mboxrd@z Thu Jan  1 00:00:00 1970
From: john@feith.com (John Wehle)
To: law@cygnus.com
Cc: egcs@cygnus.com
Subject: Re: Performance measurements 
Date: Sat, 27 Jun 1998 15:52:00 -0000
Message-id: <199806272148.RAA21864@jwlab.FEITH.COM>
X-SW-Source: 1998-06/msg01011.html

> Here's some more info.  PPro200
> 
> egcs-1.0.3	 69.96
> today's sources	 70.40
> 
> Note I get 73.14 if I remove all the various -malign switches.
> 
> Not particularly good.    Can someone look into this?  It might
> be another case of double alignment losing badly.  I don't know
> x86 issues well enough.

Part of the problem is due to loop turning:

(insn 73 71 74 (set (reg:DF 49)
        (mem/s:DF (plus:SI (plus:SI (mult:SI (reg/v:SI 29)
                        (const_int 8))
                    (reg/v:SI 21))
                (const_int 16)))) 74 {movdf+1} (nil)
    (nil))

(insn 74 73 75 (set (reg:DF 50)
        (mult:DF (reg:DF 48)
            (reg:DF 49))) 360 {ffshi_1+1} (nil)
    (nil))

into:

(insn 73 69 74 (set (reg:DF 49)
        (mem/s:DF (reg:SI 104))) -1 (nil)
    (nil))

(insn 74 73 75 (set (reg:DF 50)
        (mult:DF (reg:DF 48)
            (reg:DF 49))) -1 (nil)
    (nil))

which global register allocation turns into:

(insn 295 298 74 (set (reg:SI 2 %ecx)
        (mem:SI (plus:SI (reg:SI 7 %esp)
                (const_int 16)))) -1 (nil)
    (nil))

(insn:HI 74 295 75 (set (reg:DF 9 %st(1))
        (mult:DF (reg:DF 9 %st(1))
            (mem/s:DF (reg:SI 2 %ecx)))) 360 {ffshi_1+1} (nil)
    (nil))

because it had to spill (reg:SI 104) since the Intel 386 is a
register poor machine.  Defining DONT_REDUCE_ADDR when builting
egcs results in:

(insn:HI 74 379 75 (set (reg:DF 9 %st(1))
        (mult:DF (reg:DF 9 %st(1))
            (mem/s:DF (plus:SI (plus:SI (mult:SI (reg/v:SI 0 %eax)
                            (const_int 8))
                        (reg:SI 2 %ecx))
                    (const_int 16))))) 360 {ffshi_1+1} (nil)
    (nil))

after global register allocation.  The corresponding benchmark
results on a 233 MHz Pentium II running FreeBSD 3.0 are:

egcs-19980621 aout: 87.91 MFLOPS
egcs-19980621 elf: 86.85 MFLOPS

egcs-19980621 DONT_REDUCE_ADDR aout: 105.24 MFLOPS
egcs-19980621 DONT_REDUCE_ADDR elf: 105.24 MFLOPS

Possible solutions:

  1) Don't call find_mem_givs if SMALL_REGISTER_CLASSES.

  2) Don't consider the giv if SMALL_REGISTER_CLASSES and it's a valid
     memory address for the machine.

  3) Consider the giv but don't take an action which will result in
     a new register / (more registers then before) if SMALL_REGISTER_CLASSES
     and the giv is a valid memory address for the machine.

BTW, I'm pulling these solutions out of thin air as I'm not up to speed
with the operation of loop.

-- John
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