http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53227
Bug #: 53227
Summary: [4.8 Regression] FAIL: gcc.target/i386/movbe-2.c
scan-assembler-times movbe[ \t] 4
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Keywords: ra
Severity: normal
Priority: P3
Component: rtl-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: ubiz...@gmail.com
CC: ber...@gcc.gnu.org, uweig...@gcc.gnu.org,
vmaka...@gcc.gnu.org
Target: i686
Split from PR 53176, that changed lower-subreg to not split subregs early on
x86.
Following testcase
--cut here--
extern long long x;
void
foo (long long i)
{
x = __builtin_bswap64 (i);
}
long long
bar ()
{
return __builtin_bswap64 (x);
}
--cut here--
compiled with -O2 -mmovbe -m32 on x86 target triggers RA to allocate
non-optimal registers for "foo" (and forcing reload), while it is able to
allocate optimal regs for "bar" case:
bar:
movbe x+4, %eax
movbe x, %edx
ret
The situation with foo:
foo:
pushl %ebx
movl 8(%esp), %eax
movl 12(%esp), %edx
movl %eax, %ebx
movl %edx, %ecx
bswap %ebx
bswap %ecx
movl %ebx, x+4
movl %ecx, x
popl %ebx
ret
Which is a noticeable regression from 4.7:
foo:
movbe 4(%esp), %eax
movbe 8(%esp), %edx
movl %eax, x+4
movl %edx, x
ret
Adding -mregparm=2 does not improve things:
foo:
pushl %ebx
movl %edx, %ecx
movl %eax, %ebx
bswap %ecx
bswap %ebx
movl %ecx, x
movl %ebx, x+4
popl %ebx
ret
while 4.7 generates:
foo:
movbe %edx, x
movbe %eax, x+4
ret
