arm.c (arm_gen_constant): Add new heuristic for generating constant integers…

arm.c (arm_gen_constant): Add new heuristic for generating constant integers that can be expressed as the...

	* arm.c (arm_gen_constant): Add new heuristic for generating
	constant integers that can be expressed as the difference of two
	valid immediates.

From-SVN: r99472

gcc/ChangeLog

+2005-05-09  Richard Earnshaw  <richard.earnshaw@arm.com>
+
+	* arm.c (arm_gen_constant): Add new heuristic for generating
+	constant integers that can be expressed as the difference of two
+	valid immediates.
+
 2005-05-09  Roger Sayle  <roger@eyesopen.com>
 
 	* c-tree.h (parser_build_unary_op): New prototype.

gcc/config/arm/arm.c

@@ -1531,8 +1531,8 @@ use_return_insn (int iscond, rtx sibling)
 int
 const_ok_for_arm (HOST_WIDE_INT i)
 {
-  unsigned HOST_WIDE_INT mask = ~(unsigned HOST_WIDE_INT)0xFF;
-
+  int lowbit;
+  
   /* For machines with >32 bit HOST_WIDE_INT, the bits above bit 31 must
      be all zero, or all one.  */
   if ((i & ~(unsigned HOST_WIDE_INT) 0xffffffff) != 0
@@ -1541,19 +1541,24 @@ const_ok_for_arm (HOST_WIDE_INT i)
 	      & ~(unsigned HOST_WIDE_INT) 0xffffffff)))
     return FALSE;
 
-  /* Fast return for 0 and powers of 2 */
-  if ((i & (i - 1)) == 0)
+  i &= (unsigned HOST_WIDE_INT) 0xffffffff;
+  
+  /* Fast return for 0 and small values.  We must do this for zero, since
+     the code below can't handle that one case.  */
+  if ((i & ~(unsigned HOST_WIDE_INT) 0xff) == 0)
     return TRUE;
 
-  do
-    {
-      if ((i & mask & (unsigned HOST_WIDE_INT) 0xffffffff) == 0)
-        return TRUE;
-      mask =
-	  (mask << 2) | ((mask & (unsigned HOST_WIDE_INT) 0xffffffff)
-			  >> (32 - 2)) | ~(unsigned HOST_WIDE_INT) 0xffffffff;
-    }
-  while (mask != ~(unsigned HOST_WIDE_INT) 0xFF);
+  /* Get the number of trailing zeros, rounded down to the nearest even
+     number.  */
+  lowbit = (ffs ((int) i) - 1) & ~1;
+
+  if ((i & ~(((unsigned HOST_WIDE_INT) 0xff) << lowbit)) == 0)
+    return TRUE;
+  else if (lowbit <= 4
+	   && ((i & ~0xc000003f) == 0
+	       || (i & ~0xf000000f) == 0
+	       || (i & ~0xfc000003) == 0))
+    return TRUE;
 
   return FALSE;
 }