Re: optimization/8794: optimization improperly eliminates certain expressions

["Christian Ehrhardt" <ehrhardt@mathematik.uni-ulm.de>]

The following reply was made to PR optimization/8794; it has been noted by GNATS.

From: "Christian Ehrhardt" <ehrhardt@mathematik.uni-ulm.de>
To: pageexec@freemail.hu
Cc: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org
Subject: Re: optimization/8794: optimization improperly eliminates certain expressions
Date: Tue, 3 Dec 2002 17:24:08 +0100

 On Tue, Dec 03, 2002 at 02:29:05PM -0000, pageexec@freemail.hu wrote:
 > >Number:         8794
 > >Category:       optimization
 > >Synopsis:       optimization improperly eliminates certain expressions
 > >Release:        gcc 3.2.1
 
 Confirmed on i686. The orignal example works ok on sparc but a slightly
 simplified example produces bad code on sparc with 3.2.1 and 3.3:
 
 ------------- cut ------------------
 unsigned int addr;
 void f (void)
 {
 	addr = (1024 & (1024UL - (addr & 1023UL)));
 }
 ------------- cut ------------------
 
 Is compiled into:
 
 ------------- cut ------------------
 	.file	"8794.c"
 	.section	".text"
 	.align 4
 	.global f
 	.type	f,#function
 	.proc	020
 f:
 	!#PROLOGUE# 0
 	!#PROLOGUE# 1
 	mov	1024, %o1
 	sethi	%hi(addr), %o0
 	retl
 	st	%o1, [%o0+%lo(addr)]
 .LLfe1:
 	.size	f,.LLfe1-f
 	.common	addr,4,4
 	.ident	"GCC: (GNU) 3.2.1 20021111 (prerelease)"
 ------------- cut ------------------
 
 Which is clearly wrong. The necessary instructions are elimiated by
 between 8794.c.15.life and 8794.c.16.combine.
 
       regards   Christian
 
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