------- Comment #5 from matz at gcc dot gnu dot org 2010-02-05 15:36 -------
The code for the if() looks sane on x86-64:
-----------------------------------------
;; if (D.2729_8 != 0)
(insn 16 15 17 pr42972.c:10 (set (reg:QI 87)
(mem/s:QI (reg/f:DI 82 [ D.2727 ]) [0 S1 A32])) -1 (nil))
(insn 17 16 18 pr42972.c:10 (parallel [
(set (reg:QI 86)
(and:QI (reg:QI 87)
(const_int 1 [0x1])))
(clobber (reg:CC 17 flags))
]) -1 (expr_list:REG_EQUAL (and:QI (mem/s:QI (reg/f:DI 82 [ D.2727 ])
[0 S1 A32])
(const_int 1 [0x1]))
(nil)))
(insn 18 17 19 pr42972.c:10 (set (reg:CCZ 17 flags)
(compare:CCZ (reg:QI 86)
(const_int 0 [0x0]))) -1 (nil))
(jump_insn 19 18 0 pr42972.c:10 (set (pc)
(if_then_else (eq (reg:CCZ 17 flags)
(const_int 0 [0x0]))
(label_ref 0)
(pc))) -1 (expr_list:REG_BR_PROB (const_int 5000 [0x1388])
(nil)))
---------------------------------
Btw, instructions marked for forwarding (by TER) are not expanded to useless
code, but not expanded at all (or better said, only at the point of use).
The back-and-forth between QImode and SImode on arm seems to stem from
register promotion trying really hard to work on only SImode regs.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42972
