combine.c (expand_compound_operation): Do not convert ZERO_EXTEND to SIGN_EXTEND...

	* combine.c (expand_compound_operation): Do not convert ZERO_EXTEND to
	SIGN_EXTEND, convert SIGN_EXTEND to ZERO_EXTEND.
	(make_compound_operation): Choose cheaper alternative between
	ZERO_EXTEND and SIGN_EXTEND when sign bit is not set.

From-SVN: r31180

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 3bdb03a06eae51278b169b5fc5ced27f1efdd60f..61ce55b04c03e10b028135d5e2750393d533b49c 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,10 @@
 Mon Jan  3 15:33:37 MET 2000  Jan Hubicka  <hubicka@freesoft.cz>
 
+       * combine.c (expand_compound_operation): Do not convert ZERO_EXTEND to
+       SIGN_EXTEND, convert SIGN_EXTEND to ZERO_EXTEND.
+       (make_compound_operation): Choose cheaper alternative between
+       ZERO_EXTEND and SIGN_EXTEND when sign bit is not set.
+
        * regclass.c (op_costs): Remove global variable.
        (record_reg_classes): New parameter "op_costs" and "reg_pref".
        (record_operand_costs): Break out from ...

diff --git a/gcc/combine.c b/gcc/combine.c
index 3599168769f0d70da86bb032ba20d2e17bc359d9..2cb0c4561ab07895973cfbb188392343f7e38147 100644 (file)
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -5486,6 +5486,20 @@ expand_compound_operation (x)
     default:
       return x;
     }
+  /* Convert sign extension to zero extension, if we know that the high
+     bit is not set, as this is easier to optimize.  It will be converted
+     back to cheaper alternative in make_extraction.  */
+  if (GET_CODE (x) == SIGN_EXTEND
+      && (GET_MODE_BITSIZE (GET_MODE (x)) <= HOST_BITS_PER_WIDE_INT
+         && ((nonzero_bits (XEXP (x, 0), GET_MODE (XEXP (x, 0)))
+               & ~ (((unsigned HOST_WIDE_INT)
+                     GET_MODE_MASK (GET_MODE (XEXP (x, 0))))
+                    >> 1))
+              == 0)))
+    {
+      rtx temp = gen_rtx_ZERO_EXTEND (GET_MODE (x), XEXP (x, 0));
+      return expand_compound_operation (temp);
+    }
 
   /* We can optimize some special cases of ZERO_EXTEND.  */
   if (GET_CODE (x) == ZERO_EXTEND)
@@ -5533,30 +5547,6 @@ expand_compound_operation (x)
              & ~ GET_MODE_MASK (GET_MODE (XEXP (x, 0)))) == 0)
        return SUBREG_REG (XEXP (x, 0));
 
-      /* If sign extension is cheaper than zero extension, then use it
-        if we know that no extraneous bits are set, and that the high
-        bit is not set.  */
-      if (flag_expensive_optimizations
-         && ((GET_MODE_BITSIZE (GET_MODE (x)) <= HOST_BITS_PER_WIDE_INT
-              && ((nonzero_bits (XEXP (x, 0), GET_MODE (x))
-                   & ~ (((unsigned HOST_WIDE_INT)
-                         GET_MODE_MASK (GET_MODE (XEXP (x, 0))))
-                        >> 1))
-                  == 0))
-             || (GET_RTX_CLASS (GET_CODE (XEXP (x, 0))) == '<'
-                 && (GET_MODE_BITSIZE (GET_MODE (XEXP (x, 0)))
-                     <= HOST_BITS_PER_WIDE_INT)
-                 && (((HOST_WIDE_INT) STORE_FLAG_VALUE
-                      & ~ (((unsigned HOST_WIDE_INT)
-                            GET_MODE_MASK (GET_MODE (XEXP (x, 0))))
-                           >> 1))
-                     == 0))))
-       {
-         rtx temp = gen_rtx_SIGN_EXTEND (GET_MODE (x), XEXP (x, 0));
-
-         if (rtx_cost (temp, SET) < rtx_cost (x, SET))
-           return expand_compound_operation (temp);
-       }
     }
 
   /* If we reach here, we want to return a pair of shifts.  The inner
@@ -5894,12 +5884,35 @@ make_extraction (mode, inner, pos, pos_rtx, len,
                   ? gen_rtx_CLOBBER (tmode, const0_rtx)
                   : gen_rtx_combine (STRICT_LOW_PART, VOIDmode, new)));
 
+      if (mode == tmode)
+       return new;
+
+      /* If we know that no extraneous bits are set, and that the high
+        bit is not set, convert the extraction to the cheaper of
+        sign and zero extension, that are equivalent in these cases.  */
+      if (flag_expensive_optimizations
+         && (GET_MODE_BITSIZE (tmode) <= HOST_BITS_PER_WIDE_INT
+             && ((nonzero_bits (new, tmode)
+                  & ~ (((unsigned HOST_WIDE_INT)
+                        GET_MODE_MASK (tmode))
+                       >> 1))
+                 == 0)))
+       {
+         rtx temp = gen_rtx_ZERO_EXTEND (mode, new);
+         rtx temp1 = gen_rtx_SIGN_EXTEND (mode, new);
+
+         /* Prefer ZERO_EXTENSION, since it gives more information to
+            backends.  */
+         if (rtx_cost (temp, SET) < rtx_cost (temp1, SET))
+           return temp;
+         return temp1;
+       }
+
       /* Otherwise, sign- or zero-extend unless we already are in the
         proper mode.  */
 
-      return (mode == tmode ? new
-             : gen_rtx_combine (unsignedp ? ZERO_EXTEND : SIGN_EXTEND,
-                                mode, new));
+      return (gen_rtx_combine (unsignedp ? ZERO_EXTEND : SIGN_EXTEND,
+                              mode, new));
     }
 
   /* Unless this is a COMPARE or we have a funny memory reference,
@@ -6088,7 +6101,30 @@ make_extraction (mode, inner, pos, pos_rtx, len,
      have to zero extend.  Otherwise, we can just use a SUBREG.  */
   if (pos_rtx != 0
       && GET_MODE_SIZE (pos_mode) > GET_MODE_SIZE (GET_MODE (pos_rtx)))
-    pos_rtx = gen_rtx_combine (ZERO_EXTEND, pos_mode, pos_rtx);
+    {
+      rtx temp = gen_rtx_combine (ZERO_EXTEND, pos_mode, pos_rtx);
+
+      /* If we know that no extraneous bits are set, and that the high
+        bit is not set, convert extraction to cheaper one - eighter
+        SIGN_EXTENSION or ZERO_EXTENSION, that are equivalent in these
+        cases.  */
+      if (flag_expensive_optimizations
+         && (GET_MODE_BITSIZE (GET_MODE (pos_rtx)) <= HOST_BITS_PER_WIDE_INT
+             && ((nonzero_bits (pos_rtx, GET_MODE (pos_rtx))
+                  & ~ (((unsigned HOST_WIDE_INT)
+                        GET_MODE_MASK (GET_MODE (pos_rtx)))
+                       >> 1))
+                 == 0)))
+       {
+         rtx temp1 = gen_rtx_SIGN_EXTEND (pos_mode, pos_rtx);
+
+         /* Preffer ZERO_EXTENSION, since it gives more information to
+            backends.  */
+         if (rtx_cost (temp1, SET) < rtx_cost (temp, SET))
+           temp = temp1;
+       }
+      pos_rtx = temp;
+    }
   else if (pos_rtx != 0
           && GET_MODE_SIZE (pos_mode) < GET_MODE_SIZE (GET_MODE (pos_rtx)))
     pos_rtx = gen_lowpart_for_combine (pos_mode, pos_rtx);