Eric,
this patch is the first half of the fix for PR61605.
The problem it addresses is the following: Consider this copy cycle (a = b; b =
a):
...
(insn 2 18 3 2 (set (reg/v:SI 1 dx [orig:86 yD.1749 ] [86])
(reg:SI 5 di [ yD.1749 ])) test.c:9 90 {*movsi_internal}
(expr_list:REG_DEAD (reg:SI 5 di [ yD.1749 ])
(nil)))
(note 3 2 6 2 NOTE_INSN_FUNCTION_BEG)
(insn 6 3 7 2 (set (reg:SI 5 di)
(reg/v:SI 1 dx [orig:86 yD.1749 ] [86])) test.c:10 90 {*movsi_internal}
(nil))
...
cprop_hardreg handles this currently in the following way:
- it processes the first copy, and sets up di as representant of dx.
- it then processes the second copy, and replaces the dx with di:
...
(insn 6 3 7 2 (set (reg:SI 5 di)
(reg:SI 5 di [orig:86 yD.1749 ] [86])) test.c:10 90 {*movsi_internal}
(nil))
...
turning it into a noop.
pass_fast_rtl_dce subsequently removes the noop.
However, while processing the second copy, it considers the set of di in insn 6
as killing, and removes di as representant of dx. So a use of dx in a following
insn is not replaced by di.
By running pass_cprop_hardreg once more after pass_fast_rtl_dce, we do manage to
replace the use of dx in a following insn by di.
This patch achieves the same, without rerunning pass_cprop_hardreg. It ensures
in copyprop_hardreg_forward_1 that the set of a dest by a noop is not considered
killing.
Bootstrapped and reg-tested on x86_64.
OK for trunk?
Thanks,
- Tom
2014-10-13 Tom de Vries <t...@codesourcery.com>
PR rtl-optimization/61605
* regcprop.c (copyprop_hardreg_forward_1): Add copy_p and noop_p. Don't
notice stores for noops. Don't regard noops as copies.
diff --git a/gcc/regcprop.c b/gcc/regcprop.c
index 3297721..c71de98 100644
--- a/gcc/regcprop.c
+++ b/gcc/regcprop.c
@@ -1032,12 +1032,21 @@ copyprop_hardreg_forward_1 (basic_block bb, struct value_data *vd)
note_stores (PATTERN (insn), kill_clobbered_value, vd);
}
- /* Notice stores. */
- note_stores (PATTERN (insn), kill_set_value, &ksvd);
+ bool copy_p = (set
+ && REG_P (SET_DEST (set))
+ && REG_P (SET_SRC (set)));
+ bool noop_p = (copy_p
+ && rtx_equal_p (SET_DEST (set), SET_SRC (set)));
- /* Notice copies. */
- if (set && REG_P (SET_DEST (set)) && REG_P (SET_SRC (set)))
- copy_value (SET_DEST (set), SET_SRC (set), vd);
+ if (!noop_p)
+ {
+ /* Notice stores. */
+ note_stores (PATTERN (insn), kill_set_value, &ksvd);
+
+ /* Notice copies. */
+ if (copy_p)
+ copy_value (SET_DEST (set), SET_SRC (set), vd);
+ }
if (insn == BB_END (bb))
break;
--
1.9.1
