From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.4 required=5.0 tests=BAYES_00,UNCLOSED_BRACKET
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Thread: 103376,6b8760de26d569f1
X-Google-NewGroupId: yes
X-Google-Attributes: gida07f3367d7,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII
Path: 
 g2news1.google.com!news1.google.com!news.glorb.com!usenet.stanford.edu!newsfeed.berkeley.edu!ucberkeley!newsfeed.arcor.de!newsspool1.arcor-online.net!news.arcor.de.POSTED!not-for-mail
Date: Thu, 07 Apr 2011 19:10:52 +0200
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US;
 rv:1.9.2.15) Gecko/20110303 Thunderbird/3.1.9
MIME-Version: 1.0
Newsgroups: comp.lang.ada
Subject: Re: gnat 4.4.5 generates surprising code when enabling FP checks
References: <inkmbf$lhb$1@speranza.aioe.org>
In-Reply-To: <inkmbf$lhb$1@speranza.aioe.org>
Content-Type: text/plain; charset=ISO-8859-15
Content-Transfer-Encoding: 8bit
Message-ID: <4d9df01c$0$7669$9b4e6d93@newsspool1.arcor-online.net>
Organization: Arcor
NNTP-Posting-Date: 07 Apr 2011 19:10:52 CEST
NNTP-Posting-Host: 66090db2.newsspool1.arcor-online.net
X-Trace: 
 DXC=223_aV2P690RadXUBHgFh3ic==]BZ:af>4Fo<]lROoR1<`=YMgDjhg2gJjA2iN6Xi6nc\616M64>:Lh>_cHTX3j=GlH8hLIN[[5
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news1.google.com comp.lang.ada:18706
Date: 2011-04-07T19:10:52+02:00
List-Id: <comp.lang.ada>

On 07.04.11 17:48, Markus Sch�pflin wrote:
> What really surprises me is that in the resulting assembler
> code the last multiplication is actually performed twice, the disassembled
> object code looks like this (for the last check and multiplication only):

(I noticed that a big portion of the code is for performing
the validity checks requested via -gnatVa; lots of detail
documented in function Valid's body in System.Fat_Gen
(that I do not fully understand).  system__fat_sflt__attr_short_float__valid
refers to an instance of Fat_Gen (Short_Float), a package that
implements floating point attribute functions, IIUC.

(I also noticed that there is a conditional jump after
the call on system__fat_sflt__attr_short_float__valid
to after the second multiplication.)

>  8048ed6:       d9 45 e4                flds   -0x1c(%ebp)
>  8048ed9:       d8 4d e0                fmuls  -0x20(%ebp)
>  8048edc:       c7 44 24 04 00 00 00    movl   $0x0,0x4(%esp)
>  8048ee3:       00
>  8048ee4:       89 3c 24                mov    %edi,(%esp)
>  8048ee7:       d9 5d dc                fstps  -0x24(%ebp)
>  8048eea:       e8 61 fc ff ff          call   8048b50
> <system__fat_sflt__attr_short_float__valid@plt>
>  8048eef:       84 c0                   test   %al,%al
>  8048ef1:       74 2c                   je     8048f1f <_ada_float_checks+0xaf>
>  8048ef3:       83 c3 01                add    $0x1,%ebx
>  8048ef6:       d9 45 e4                flds   -0x1c(%ebp)
>  8048ef9:       81 fb 11 27 00 00       cmp    $0x2711,%ebx
>  8048eff:       d8 4d e0                fmuls  -0x20(%ebp)
>  8048f02:       dd d8                   fstp   %st(0)
> 
> Is the second multiplication to be expected? Does anybody know if there is an
> optimizer option which would eliminate the second multiplication?

Since much of the generated code is a consequence of -gnatVA
(which implies -gnatVf), shouldn't a smaller selection validity
checking do the trick, i.e. if you exclude -gnatVf?

Of course this doesn't answer the question if -gnatVa must be used.
HTH