------- Comment #7 from pinskia at gcc dot gnu dot org 2008-09-20 23:32 -------
(In reply to comment #4)
> This might be a cost issue in the ppc backend (and so target, not
> rtl-optimization).
GCSE is pulling out the invariant.
Before GCSE we had:
(insn 20 5 6 3 t.c:6 (set (reg/f:SI 121)
(plus:SI (reg/f:SI 113 sfp)
(const_int 8 [0x8]))) -1 (nil))
(insn 6 20 7 3 t.c:6 (set (reg:SI 3 3)
(reg/f:SI 121)) 325 {*movsi_internal1} (expr_list:REG_EQUAL (plus:SI
(reg/f:SI 113 sfp)
(const_int 8 [0x8]))
(nil)))
(call_insn 7 6 8 3 t.c:6 (parallel [
(set (reg:SI 3 3)
(call (mem:SI (symbol_ref:SI ("f0") [flags 0x41] <function_decl
0xf7d41e00 f0>) [0 S4 A8])
(const_int 0 [0x0])))
(use (const_int 0 [0x0]))
(clobber (reg:SI 65 lr))
]) 450 {*call_value_nonlocal_sysvsi} (nil)
(expr_list:REG_DEP_TRUE (use (reg:SI 3 3))
(nil)))
(insn 8 7 10 3 t.c:6 (set (reg:SI 119 [ D.1255 ])
(reg:SI 3 3)) 325 {*movsi_internal1} (nil))
(insn 10 8 11 3 t.c:6 (set (reg:CC 120)
(compare:CC (reg:SI 119 [ D.1255 ])
(const_int 0 [0x0]))) 471 {*cmpsi_internal1} (nil))
(jump_insn 11 10 19 3 t.c:6 (set (pc)
(if_then_else (ne (reg:CC 120)
(const_int 0 [0x0]))
(label_ref 9)
(pc))) 560 {*rs6000.md:13857} (expr_list:REG_BR_PROB (const_int
8600 [0x2198])
(nil)))
And then it pulled out the set outside of the loop.
Why didn't we combine the set of reg 121 into its one use in the set of 3
before the fact (like in fwprop)?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36758
