--- Comment #1 from ubizjak at gmail dot com 2007-01-13 23:27 ---
Addition (addl) operates in CCGOCmode and is not compatible with requested
CCZmode. Following that, test insn will be eliminated in this example:
int add_zf(int *x, int y, int a, int b)
{
if ((*x + y) 0)
return a;
else
return b;
}
add_zf:
addl(%rdi), %esi
movl%edx, %eax
cmovns %ecx, %eax
ret
However, having assignment to *x, we enter RTL generation with:
bb 2:
D.1972 = *x;
temp.27 = y + D.1972;
*x = temp.27;
if (temp.27 0) goto L2; else goto L3;
this gets expanded into:
;; D.1972 = *x
(insn 14 12 0 (set (reg:SI 59 [ D.1972 ])
(mem:SI (reg/v/f:DI 61 [ x ]) [2 S4 A32])) -1 (nil)
(nil))
;; temp.27 = y + D.1972
(insn 15 14 0 (parallel [
(set (reg:SI 58 [ temp.27 ])
(plus:SI (reg/v:SI 62 [ y ])
(reg:SI 59 [ D.1972 ])))
(clobber (reg:CC 17 flags))
]) -1 (nil)
(nil))
;; *x = temp.27
(insn 16 15 0 (set (mem:SI (reg/v/f:DI 61 [ x ]) [2 S4 A32])
(reg:SI 58 [ temp.27 ])) -1 (nil)
(nil))
;; if (temp.27 0) goto L2;
(insn 17 16 18 (set (reg:CCGOC 17 flags)
(compare:CCGOC (reg:SI 58 [ temp.27 ])
(const_int 0 [0x0]))) -1 (nil)
(nil))
Combine pass then creates:
(insn 15 14 16 2 (parallel [
(set (reg:SI 58 [ temp.27 ])
(plus:SI (reg/v:SI 62 [ y ])
(mem:SI (reg/v/f:DI 61 [ x ]) [2 S4 A32])))
(clobber (reg:CC 17 flags))
]) 207 {*addsi_1} (insn_list:REG_DEP_TRUE 6 (insn_list:REG_DEP_TRUE 7
(nil)))
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_DEAD (reg/v:SI 62 [ y ])
(nil
(insn 16 15 40 2 (set (mem:SI (reg/v/f:DI 61 [ x ]) [2 S4 A32])
(reg:SI 58 [ temp.27 ])) 40 {*movsi_1} (insn_list:REG_DEP_TRUE 15
(nil))
(expr_list:REG_DEAD (reg/v/f:DI 61 [ x ])
(nil)))
(insn 40 16 41 2 (set (reg:CCGOC 17 flags)
(compare:CCGOC (reg:SI 58 [ temp.27 ])
(const_int 0 [0x0]))) 3 {*cmpsi_ccno_1} (nil)
(expr_list:REG_DEAD (reg:SI 58 [ temp.27 ])
(nil)))
Unfortunatelly, combine pass will not create a combination of insn 15 and insn
16 because reg 58 is not dead in insn 16. However, combination of insn 15, insn
16 _and_ insn 40 would produce correct pattern and something similar to your
proposed asm (cmovns instead of cmovne).
--
ubizjak at gmail dot com changed:
What|Removed |Added
CC||ubizjak at gmail dot com
Severity|normal |enhancement
Status|UNCONFIRMED |NEW
Component|target |rtl-optimization
Ever Confirmed|0 |1
Known to fail||4.3.0
Last reconfirmed|-00-00 00:00:00 |2007-01-13 23:27:24
date||
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30455
