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Date: Thu, 25 Sep 2003 16:56:00 -0000
From: "yamt at mwd dot biglobe dot ne dot jp" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20030925155217.12404.yamt@mwd.biglobe.ne.jp>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug optimization/12404] New: pointer to union member problem
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X-SW-Source: 2003-09/txt/msg01919.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12404

           Summary: pointer to union member problem
           Product: gcc
           Version: 3.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: yamt at mwd dot biglobe dot ne dot jp
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i386-unknown-netbsdelf1.6W
  GCC host triplet: i386--netbsdelf
GCC target triplet: i386--netbsdelf

compiling the following program with -O2 for i386
yields the latter asm output.

% gcc -v
Using built-in specs.
Configured with: /usr/src/tools/gcc/../../gnu/dist/gcc/configure --enable-long-long --disable-multilib --enable-threads --build=i386-unknown-netbsdelf --host=i386--netbsdelf --target=i386--netbsdelf : (reconfigured) /usr/src/tools/gcc/../../gnu/dist/gcc/configure --enable-long-long --disable-multilib --enable-threads --build=i386-unknown-netbsdelf1.6W --host=i386--netbsdelf --target=i386--netbsdelf
Thread model: posix
gcc version 3.3.1

============================================================
#include <stdio.h>

int
main()
{
	union { int i; short s; } u[] = {{1}, {2}, {3}};

	printf("%d\n", *&u->s);
}
============================================================
	.file	"a.c"
	.section	.rodata.str1.1,"aMS",@progbits,1
.LC0:
	.string	"%d\n"
	.text
	.p2align 2,,3
.globl main
	.type	main, @function
main:
	pushl	%ebp
	movl	%esp, %ebp
	subl	$24, %esp
	andl	$-16, %esp
	subl	$8, %esp
	movswl	-24(%ebp),%eax	# <= used before initialized.
	pushl	%eax
	pushl	$.LC0
	movl	$1, -24(%ebp)	# <= initialize here
	movl	$2, -20(%ebp)
	movl	$3, -16(%ebp)
	call	printf
	leave
	ret
	.size	main, .-main
	.ident	"GCC: (GNU) 3.3.1"