Re: [PATCH, PR61605, 1/2] Handle copy cycles in pass_cprop_hardreg

[Jeff Law]

On 10/16/14 03:13, Tom de Vries wrote:

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

0001-Don-t-regard-a-copy-with-identical-src-and-dest-as-k.patch


2014-10-13  Tom de Vries

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.

OK.
Jeff

[PATCH, PR61605, 1/2] Handle copy cycles in pass_cprop_hardreg

[Tom de Vries]

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  

	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