------- Comment #3 from steven at gcc dot gnu dot org 2010-03-31 15:15 -------
Well, according to GDB, combine does try to combine in try_combine:
Breakpoint 8, try_combine (i3=0x20000000004fc8b8, i2=0x20000000004fc828,
i1=0x0, new_direct_jump_p=0x60000fffffd4ae28) at ../../trunk/gcc/combine.c:2389
2389 rtx newpat, newi2pat = 0;
3: debug_rtx(i3) = (insn 9 8 10 2 t.c:8 (set (reg:CC 24 cc)
(compare:CC (reg/v:SI 134 [ fD.1273 ])
(const_int 0 [0x0]))) 220 {*arm_cmpsi_insn} (nil))
void
2: debug_rtx(i2) = (insn 8 7 9 2 t.c:7 (set (reg/v:SI 134 [ fD.1273 ])
(reg:SI 0 r0)) 658 {*thumb2_movsi_insn} (expr_list:REG_DEAD (reg:SI 0
r0)
(nil)))
But then we hit cant_combine_insn_p(i2) because r0 is LO_REGS, we're compiling
for TARGET_THUMB, and so CLASS_LIKELY_SPILLED_P (REGNO_REG_CLASS (REGNO (src)))
is true for src=r0 in this reg-reg move:
if (REG_P (src) && REG_P (dest)
&& ((REGNO (src) < FIRST_PSEUDO_REGISTER
&& ! fixed_regs[REGNO (src)]
&& CLASS_LIKELY_SPILLED_P (REGNO_REG_CLASS (REGNO (src))))
|| (REGNO (dest) < FIRST_PSEUDO_REGISTER
&& ! fixed_regs[REGNO (dest)]
&& CLASS_LIKELY_SPILLED_P (REGNO_REG_CLASS (REGNO (dest))))))
return 1;
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43597
