------- Comment #8 from uros at kss-loka dot si 2005-11-08 12:53 -------
> This patch fixes the failure for me, but...
... we actually gain nothing here.
>From .loop2_done, we have following sequence, where mem->reg load is pushed out
of the loop:
(insn 21 16 39 0 (set (reg:DF 64)
(mem/u/c/i:DF (symbol_ref/u:SI ("*.LC0") [flags 0x2]) [0 S8 A64])) -1
(nil)
(nil))
;; End of basic block 0, registers live:
(nil)
(note 39 21 17 NOTE_INSN_LOOP_BEG)
;; Start of basic block 1, registers live: (nil)
(code_label 17 39 18 1 2 "" [1 uses])
(note 18 17 47 1 [bb 1] NOTE_INSN_BASIC_BLOCK)
(insn 47 18 22 1 (set (mem:DF (plus:SI (reg/f:SI 7 sp)
(const_int 8 [0x8])) [0 S8 A32])
(reg:DF 64)) -1 (nil)
(nil))
However, in .postreload, the insn 21 (now insn 53) is moved back _into_ the
loop (why?):
(note 21 16 39 0 NOTE_INSN_DELETED)
;; End of basic block 0, registers live:
6 [bp] 7 [sp] 16 [argp] 20 [frame] 60 64
(note 39 21 17 NOTE_INSN_LOOP_BEG)
;; Start of basic block 1, registers live: 6 [bp] 7 [sp] 59 60 64
(code_label 17 39 18 1 2 "" [1 uses])
(note 18 17 53 1 [bb 1] NOTE_INSN_BASIC_BLOCK)
(insn 53 18 47 1 (set (reg:DF 8 st)
(mem/u/c/i:DF (symbol_ref/u:SI ("*.LC0") [flags 0x2]) [0 S8 A64])) 63
{*movdf_noin
teger} (nil)
(nil))
(insn 47 53 54 1 (set (mem:DF (plus:SI (reg/f:SI 7 sp)
(const_int 8 [0x8])) [0 S8 A32])
(reg:DF 8 st)) 63 {*movdf_nointeger} (nil)
(nil))
Proposed patch thus only fixes the damage. Otherwise, all this register
moving/copying doesn't gain anything, as reload fixes something on its own.
Also, REG_EQUAL notes are lost (before and after the patch). This results in
following asm:
...
movl $-1717986918, 8(%esp)
movl $1070176665, 12(%esp)
fldl -16(%ebp)
fstpl (%esp)
call dset
movl $1, %ebx
.L2:
fldl .LC0 <<< reload moves this insn back into the loop
fstpl 8(%esp)
fldl -16(%ebp)
fstpl (%esp)
call dset
incl %ebx
cmpl $4, %ebx
jne .L2
addl $36, %esp
...
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24265
