From patchwork Wed Jul 14 14:57:53 2010
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Subject: A few simple DImode improvements
Date: Wed, 14 Jul 2010 04:57:53 -0000
From: Bernd Schmidt <bernds@codesourcery.com>
X-Patchwork-Id: 58909
Message-Id: <4C3DD071.6040707@codesourcery.com>
To: Ian Lance Taylor <iant@google.com>
Cc: Eric Botcazou <ebotcazou@adacore.com>, gcc-patches@gcc.gnu.org,
 "Vladimir N. Makarov" <vmakarov@redhat.com>

On 06/29/2010 01:34 AM, Bernd Schmidt wrote:
> On 06/29/2010 01:03 AM, Ian Lance Taylor wrote:
>> I see what you're getting at.  It's unlikely, but it does happen in code
>> which examines the bits of a floating point number via a union or using
>> -fno-strict-aliasing and a type cast.  So if that code works correctly
>> if perhaps less efficiently, then I agree that checking that the mode
>> class is MODE_INT should work OK here.
> 
> Hmm.  Looking at this again now, aren't we already doing that?
> (resolve_reg_p checks whether DEST is a CONCAT)
> 
>   if (!can_decompose_p (dest)
>       || (side_effects_p (dest) && !pushing)
>       || (!SCALAR_INT_MODE_P (dest_mode)
> 	  && !resolve_reg_p (dest)
> 	  && !resolve_subreg_p (dest)))

In other words, how about the following patch?  Bootstrapped and
regression tested on i686-linux.


Bernd
* lower-subreg.c (subreg_context): New static bitmap.
	(decompose_multiword_subregs): Allocate and free it.
	(find_decomposable_subregs): Set a bit in it for a register that
	occurs in a subreg that changes mode but not size.
	(can_decompose_p): Test it instead of non_decomposable_context.


Index: lower-subreg.c
===================================================================
--- lower-subreg.c	(revision 162146)
+++ lower-subreg.c	(working copy)
@@ -63,6 +63,10 @@ static bitmap decomposable_context;
    which it can not be decomposed.  */
 static bitmap non_decomposable_context;
 
+/* Bit N in this bitmap is set if regno N is used in a subreg
+   which changes the mode but not the size.  */
+static bitmap subreg_context;
+
 /* Bit N in the bitmap in element M of this array is set if there is a
    copy from reg M to reg N.  */
 static VEC(bitmap,heap) *reg_copy_graph;
@@ -289,6 +293,7 @@ find_decomposable_subregs (rtx *px, void
 	  && !MODES_TIEABLE_P (GET_MODE (x), GET_MODE (inner)))
 	{
 	  bitmap_set_bit (non_decomposable_context, regno);
+	  bitmap_set_bit (subreg_context, regno);
 	  return -1;
 	}
     }
@@ -616,7 +621,7 @@ can_decompose_p (rtx x)
 	return (validate_subreg (word_mode, GET_MODE (x), x, UNITS_PER_WORD)
 		&& HARD_REGNO_MODE_OK (regno, word_mode));
       else
-	return !bitmap_bit_p (non_decomposable_context, regno);
+	return !bitmap_bit_p (subreg_context, regno);
     }
 
   return true;
@@ -1091,6 +1096,7 @@ decompose_multiword_subregs (void)
 
   decomposable_context = BITMAP_ALLOC (NULL);
   non_decomposable_context = BITMAP_ALLOC (NULL);
+  subreg_context = BITMAP_ALLOC (NULL);
 
   reg_copy_graph = VEC_alloc (bitmap, heap, max);
   VEC_safe_grow (bitmap, heap, reg_copy_graph, max);
@@ -1309,6 +1315,7 @@ decompose_multiword_subregs (void)
 
   BITMAP_FREE (decomposable_context);
   BITMAP_FREE (non_decomposable_context);
+  BITMAP_FREE (subreg_context);
 }
 
 /* Gate function for lower subreg pass.  */