------- Comment #3 from ubizjak at gmail dot com 2007-02-24 10:59 -------
I'm currently testing this patch:
2007-02-24 Uros Bizjak <[EMAIL PROTECTED]>
* config/i386/i386.md (expand_set_or_movmem_via_loop): Return if
GET_MODE_SIZE (mode) * unroll is less than expected_size.
testsuite/ChangeLog:
2007-02-24 Uros Bizjak <[EMAIL PROTECTED]>
* gcc.target/i386/pr30778.c: New test.
Index: config/i386/i386.c
===================================================================
--- config/i386/i386.c (revision 122286)
+++ config/i386/i386.c (working copy)
@@ -13315,13 +13315,19 @@
{
rtx out_label, top_label, iter, tmp;
enum machine_mode iter_mode;
- rtx piece_size = GEN_INT (GET_MODE_SIZE (mode) * unroll);
- rtx piece_size_mask = GEN_INT (~((GET_MODE_SIZE (mode) * unroll) - 1));
+ HOST_WIDE_INT min_size = GET_MODE_SIZE (mode) * unroll;
+ rtx piece_size = GEN_INT (min_size);
+ rtx piece_size_mask = GEN_INT (~min_size - 1);
rtx size;
rtx x_addr;
rtx y_addr;
int i;
+ /* Bail out if expected size is less than minimum size
+ that can be emitted. */
+ if (expected_size < min_size)
+ return;
+
iter_mode = GET_MODE (count);
if (iter_mode == VOIDmode)
iter_mode = word_mode;
There is also an optimization opportunity. When compiling testcase to 32bit
code (with -m32 -O2 -mtune=k8), following is generated:
init_reg_last:
pushl %ebp
movl reg_stat, %edx
xorl %eax, %eax
movl %esp, %ebp
.L2:
movl $0, (%edx,%eax)
movl $0, 4(%edx,%eax)
movl $0, 8(%edx,%eax)
movl $0, 12(%edx,%eax)
addl $16, %eax
cmpl $16, %eax <<< not needed
jb .L2 <<< not needed
addl %eax, %edx
movw $0, (%edx)
movb $0, 2(%edx)
leave
ret
We don't need to create loop in this case, as this loop will be executed only
once.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30778
