https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80695
Bug ID: 80695
Summary: gratuitous use of stxvx to store multiple pointers
Product: gcc
Version: 7.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: acsawdey at gcc dot gnu.org
CC: meissner at gcc dot gnu.org, wschmidt at gcc dot gnu.org
Target Milestone: ---
Target: powerpc64*-*-* power9
Testing 7.1.0 on power9, compiling the following code with -O3 -mcpu=power9
typedef struct _IO_FILE {
int _flags; /* High-order word is _IO_MAGIC; rest is flags. */
char* _IO_read_ptr; /* Current read pointer */
char* _IO_read_end; /* End of get area. */
char* _IO_read_base; /* Start of putback+get area. */
char* _IO_write_base; /* Start of put area. */
char* _IO_write_ptr; /* Current put pointer. */
char* _IO_write_end; /* End of put area. */
char* _IO_buf_base; /* Start of reserve area. */
char* _IO_buf_end; /* End of reserve area. */
} _IO_FILE;
int
_IO_new_file_overflow (_IO_FILE *f, int ch)
{
if (f->_IO_read_ptr == f->_IO_buf_end)
f->_IO_read_end = f->_IO_read_ptr = f->_IO_buf_base;
f->_IO_write_ptr = f->_IO_read_ptr;
f->_IO_write_base = f->_IO_write_ptr;
f->_IO_write_end = f->_IO_buf_end;
f->_IO_read_base = f->_IO_read_ptr = f->_IO_read_end;
return (unsigned char) ch;
}
results in this generated code:
_IO_new_file_overflow:
ld 10,8(3)
ld 8,64(3)
mr 9,3
cmpld 7,10,8
beq 7,.L2
ld 7,16(3)
mtvsrdd 0,8,10
li 8,24
rlwinm 3,4,0,0xff
mtvsrdd 12,10,7
li 10,40
std 7,8(9)
stxvx 12,9,8
stxvx 0,9,10
blr
.p2align 4,,15
.L2:
ld 10,56(3)
mr 7,10
mtvsrdd 0,8,10
std 10,16(3)
li 8,24
rlwinm 3,4,0,0xff
mtvsrdd 12,10,7
li 10,40
std 7,8(9)
stxvx 12,9,8
stxvx 0,9,10
blr
This is an improvement over gcc6 which used multiple mtvsrd plus xxpermdi to
accomplish the same thing. However it seems to me it would still be better just
to generate 4 std instructions. We then get rid of 2 mtvsrdd, 2 stxvx, and 2 li
instructions.
