optimization/2918: long long assignment lost

[pauli@lineo.com]

>Number:         2918
>Category:       optimization
>Synopsis:       long long assignment lost
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Wed May 23 20:06:01 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Paul Dale
>Release:        gcc version 2.95.3 20010315 (release)
>Organization:
>Environment:
Linux skaro 2.2.16-22 #1 Tue Aug 22 16:49:06 EDT 2000 i686 unknown
x86 platform cross compiling to coldfire
>Description:
When the attached C file is built using:

    $ m68k-elf-gcc -m5200 -O1 -save-temps pauli.c -c

or

    $ m68k-elf-gcc -m5200 -O2 -save-temps pauli.c -c

incorrect code is generated.  Specifically, the second assignment
in the function body is discarded.  Compiling with -O0
generates correct code.

>How-To-Repeat:
struct c {
	unsigned long long a, b;
};

void x(unsigned long *p, struct c *d)
{
	d->b	  = d->a;
	d->a	  = *p;
}
>Fix:
Declaring a volatile unsigned long temporary variable and
storing *p into here and then this variable in d->a
circumvents the problem.
>Release-Note:
>Audit-Trail:
>Unformatted: