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Date: Wed, 12 Oct 2005 15:33:00 -0000
Subject: [Bug c/24332]  New: asm label declaration may be missing aliasing info
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Message-ID: <bug-24332-11514@http.gcc.gnu.org/bugzilla/>
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From: "cbowler at ca dot ibm dot com" <gcc-bugzilla@gcc.gnu.org>
X-SW-Source: 2005-10/txt/msg01549.txt.bz2
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sparky% gcc -v
Reading specs from
/.../torolab.ibm.com/fs/projects/vabld/run/gcc/aix/gcc-3.3.2/aix52/bin/../lib/gcc-lib/powerpc-ibm-aix5.1.0.0/3.3.2/specs
Configured with: ../gcc-3.3.2/configure --disable-nls
Thread model: aix
gcc version 3.3.2

t.c:

int j asm("i");
int i;

int main() {
  i = 5;
  j = 6;
  int k = i;
  j = 7;
  return k;
}

sparky% gcc t.c
sparky% a.out
sparky% echo $?
6
sparky% gcc t.c -O
sparky% a.out
sparky% echo $?
5

In the opt case I expect a result of 6.

The problem, I suspect, is that the compiler is not aliasing 'i' and 'j' to
each other for the optimizer.  The write 'j=6' appears dead in this case, and
the optimizer is likely to remove it.

You may consider this user error, however, the compiler is able to detect this
problem because it knows 'i' and 'j' have the same symbol name.  Consequently I
suggest either an error diagnostic be issued, or the symbols should be aliased
together for the optimizer.


-- 
           Summary: asm label declaration may be missing aliasing info
           Product: gcc
           Version: 3.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: cbowler at ca dot ibm dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24332