[forwarded from http://bugs.debian.org/301746]
Matthias
Rechecked with gcc-4.0, bug submitter writes:
This is a regression from gcc-3.2 in that gcc-3.2 does not have this
problem bug gcc-3.3 does.
The attached program generates the following code on i386 with
gcc -S -O2:
...
.L2:
movl -16(%ebp), %eax
xorl %esi, %esi
testl %eax, %eax
je .L8
As you can see %eax now contains the value in -16(%ebp).
subl $12, %esp
movl -16(%ebp), %eax
gcc-3.4 decides to reload for no reason at all.
pushl %eax
call strlen
movl %eax, %esi
addl $16, %esp
.L5:
pushl %eax
pushl %edi
pushl %ebx
leal 2(%edi,%esi), %eax
pushl %eax
call malloc
movl %eax, (%esp)
movl %eax, %ebx
call mempcpy
movl -16(%ebp), %edi
Again the value of -16(%ebp) is in %edi.
addl $16, %esp
testl %edi, %edi
je .L6
movb $61, (%eax)
pushl %ecx
pushl %esi
movl -16(%ebp), %edx
gcc-3.4 decides to reload it yet again.
pushl %edx
incl %eax
pushl %eax
call mempcpy
addl $16, %esp
-----------------------------------------------
typedef unsigned int size_t;
extern size_t strlen (__const char *__s) __attribute__ ((__pure__));
extern char *strchrnul (__const char *__s, int __c) __attribute__ ((__pure__));
extern void *mempcpy (void *__restrict __dest,
__const void *__restrict __src, size_t __n) ;
extern void *malloc(size_t);
extern void setvareq(char *s, int flags);
extern char *endofname(const char *);
extern void sh_error(const char *, ...) __attribute__ ((__noreturn__));
void
setvar(const char *name, const char *val, int flags)
{
char *p, *q;
size_t namelen;
char *nameeq;
size_t vallen;
q = endofname(name);
p = strchrnul(q, '=');
namelen = p - name;
if (!namelen || p != q)
sh_error("%.*s: bad variable name", namelen, name);
vallen = 0;
if (val == ((void *)0)) {
flags |= 2;
} else {
vallen = strlen(val);
}
p = mempcpy(nameeq = malloc(namelen + vallen + 2), name, namelen);
if (val) {
*p++ = '=';
p = mempcpy(p, val, vallen);
}
*p = '\0';
setvareq(nameeq, flags | 1);
}
--
Summary: [3.4 4.0 regression] Redundant reloading from stack
frame
Product: gcc
Version: 4.0.2
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: debian-gcc at lists dot debian dot org
CC: gcc-bugs at gcc dot gnu dot org,herbert at gondor dot
apana dot org dot au
GCC target triplet: i486-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23451
