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Re: optimization/8794: optimization improperly eliminates certain expressions
- From: "Christian Ehrhardt" <ehrhardt at mathematik dot uni-ulm dot de>
- To: pageexec at freemail dot hu
- Cc: gcc-gnats at gcc dot gnu dot org, gcc-bugs at gcc dot gnu dot org
- Date: Tue, 3 Dec 2002 17:24:08 +0100
- Subject: Re: optimization/8794: optimization improperly eliminates certain expressions
- References: <20021203142905.17186.qmail@sources.redhat.com>
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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