------- Additional Comments From steven at gcc dot gnu dot org 2005-04-10
17:24 -------
After CSE1 (t.c.04.cse) we have:
(insn 20 18 22 1 (set (reg:DI 66)
(mem/u/c:DI (const:DI (unspec:DI [
(symbol_ref:DI ("bar") [flags 0x40] <var_decl
0x2a95a2f000 bar>)
] 2)) [0 S8 A8])) 81 {*movdi_1_rex64} (nil)
(nil))
(insn 22 20 23 1 (set (reg:DI 68)
(const_int 2147483648 [0x80000000])) 81 {*movdi_1_rex64} (nil)
(nil))
(insn 23 22 24 1 (parallel [
(set (reg:DI 67)
(plus:DI (reg:DI 66)
(reg:DI 68)))
(clobber (reg:CC 17 flags))
]) 193 {*adddi_1_rex64} (nil)
(expr_list:REG_EQUAL (const:DI (plus:DI (symbol_ref:DI ("bar") [flags
0x40] <var_decl 0x2a95a2f000 bar>)
(const_int 2147483648 [0x80000000])))
(nil)))
but old loop (t.c.06.loop) somehow turns this into:
(insn 45 48 46 0 (set (reg:DI 69)
(mem/u/c:DI (const:DI (unspec:DI [
(symbol_ref:DI ("bar") [flags 0x40] <var_decl
0x2a95a2f000 bar>)
] 2)) [0 S8 A8])) -1 (nil)
(nil))
(insn 46 45 41 0 (set (reg/f:DI 67)
(plus:DI (reg:DI 69)
(const_int 2147483648 [0x80000000]))) -1 (nil)
(expr_list:REG_EQUAL (const:DI (plus:DI (symbol_ref:DI ("bar") [flags
0x40] <var_decl 0x2a95a2f000 bar>)
(const_int 2147483648 [0x80000000])))
(nil)))
Note how we have lost a clobber and turned a reg+reg addition into a reg+imm;
from:
(set (reg:DI 66) (mem:DI (const:DI (unspec:DI [(symbol_ref:DI ("bar"))]))))
(set (reg:DI 68) (const_int 2147483648 [0x80000000]))
(parallel [
(set (reg:DI 67) (plus:DI (reg:DI 66) (reg:DI 68)))
(clobber (reg:CC 17 flags))])
to:
(set (reg:DI 69) (mem:DI (const:DI (unspec:DI [(symbol_ref:DI ("bar"))]))))
(set (reg/f:DI 67) (plus:DI (reg:DI 69) (const_int 2147483648 [0x80000000])))
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20928
