Xref:	news2.mv.net comp.os.msdos.djgpp:2566
From:	Stephen Davies <pjdavies AT werple DOT mira DOT net DOT au>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Optimization error in GCC 2.7.2???
Date:	Tue, 09 Apr 1996 16:30:00 -0700
Organization:	werple public-access Internet
Lines:	11
Message-ID:	<316AF2F8.49BA@werple.mira.net.au>
NNTP-Posting-Host:	dp-m-b57.werple.net.au
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

I had some code which left-shift-equaled 1 to 128 then back 1 in a loop,
( bit<<=1 ) extracting 1-bit data from an array of chars. 
(A 2-colour font, actually.)
 The code something like: if(data[i] & bit) PutPixel(x,y,col) (C++)
 When optimizing with -O6 (Allegro 2.0 uses 6, even though docs say 0-3)
The "& bit" is optimized out of existence! Without optimization it 
stayed. This could be a pretty serious bug!
 I worked around it by doing it step by step outside the "if", but it 
would be slower.

 Stephen Davies

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