diff mbox

[PR65768] Check rtx_cost when propagating constant

Message ID 556BC156.8040209@linaro.org
State New
Headers show

Commit Message

Kugan Vivekanandarajah June 1, 2015, 2:20 a.m. UTC 
On 30/05/15 14:54, Jeff Law wrote:
> On 05/29/2015 12:32 AM, Kugan wrote:
>>>>>
>>>>>      PR target/65768
>>>>>      * cprop.c (try_replace_reg): Check cost of constants before
>>>>> propagating.
>>> I should have also noted, fresh bootstrap & regression test is needed
>>> too.
>>
>> Thanks Jeff for the comments. I did a fresh bootstrap and regression
>> testing on x86_64-linux-gnu with no new regression. I will wait for
>> you ACK.
> Can you address the 3 issues in my prior message?  I'll include them
> here for clarity:
> 
> -- 
> 
> The "const_p" variable is poorly named, though I can kindof see how you
> settled on it.  Maybe "check_rtx_costs" or something along those lines
> would be better.
> 
> The comment for the second hunk would probably be better as:
> 
> /* If TO is a constant, check the cost of the set after propagation
>    to the cost of the set before the propagation.  If the cost is
>    higher, then do not replace FROM with TO.  */
> 
> 
> You should try to produce a testcase where this change shows a code
> generation improvement.    Given we're checking target costs, that test
> will naturally be target specific.  But please do try.
> 
> So with the two nits fixed and a testcase, I think this can go forward.
> -- 
> 

Thanks Jeff and apologies for missing your previous email. I have now
fixed the comments as you suggested and changed the PR target/65768
testcase such that it tests this case.

I will commit it if there is no objections to this.

Thanks,
Kugan

gcc/ChangeLog:

2015-06-01  Kugan Vivekanandarajah  <kuganv@linaro.org>
	    Zhenqiang Chen  <zhenqiang.chen@linaro.org>

	PR target/65768
	* cprop.c (try_replace_reg): Check cost of constants before propagating.


gcc/testsuite/ChangeLog:

2015-06-01  Kugan Vivekanandarajah  <kuganv@linaro.org>

	PR target/65768
	* gcc.target/arm/maskdata.c: Remove -fno-gcse.
diff mbox

Patch

diff --git a/gcc/cprop.c b/gcc/cprop.c
index 57c44ef..94bb064 100644
--- a/gcc/cprop.c
+++ b/gcc/cprop.c
@@ -765,12 +765,37 @@  try_replace_reg (rtx from, rtx to, rtx_insn *insn)
   int success = 0;
   rtx set = single_set (insn);
 
+  bool check_rtx_costs = true;
+  bool speed = optimize_bb_for_speed_p (BLOCK_FOR_INSN (insn));
+  int old_cost = set ? set_rtx_cost (set, speed) : 0;
+
+  if ((note != 0
+      && REG_NOTE_KIND (note) == REG_EQUAL
+      && (GET_CODE (XEXP (note, 0)) == CONST
+	  || CONSTANT_P (XEXP (note, 0))))
+      || (set && CONSTANT_P (SET_SRC (set))))
+    check_rtx_costs = false;
+
   /* Usually we substitute easy stuff, so we won't copy everything.
      We however need to take care to not duplicate non-trivial CONST
      expressions.  */
   to = copy_rtx (to);
 
   validate_replace_src_group (from, to, insn);
+
+  /* If TO is a constant, check the cost of the set after propagation
+     to the cost of the set before the propagation.  If the cost is
+     higher, then do not replace FROM with TO.  */
+
+  if (check_rtx_costs
+      && CONSTANT_P (to)
+      && (set_rtx_cost (set, speed) > old_cost))
+    {
+      cancel_changes (0);
+      return false;
+    }
+
+
   if (num_changes_pending () && apply_change_group ())
     success = 1;
 
diff --git a/gcc/testsuite/gcc.target/arm/maskdata.c b/gcc/testsuite/gcc.target/arm/maskdata.c
index 6d6bb39..35d2f06 100644
--- a/gcc/testsuite/gcc.target/arm/maskdata.c
+++ b/gcc/testsuite/gcc.target/arm/maskdata.c
@@ -1,5 +1,5 @@ 
 /* { dg-do compile } */
-/* { dg-options " -O2 -fno-gcse " }  */
+/* { dg-options " -O2" }  */
 /* { dg-require-effective-target arm_thumb2_ok } */
 
 #define MASK 0xff00ff