re PR middle-end/18293 (Redundant copy operation introduced by expand)

	PR middle-end/18293
	* expmed.c (EXACT_POWER_OF_2_OR_ZERO_P): Move definition earlier.
	(expand_mult): Special case powers of two to avoid synth_mult.
	* loop.c (product_cheap_p): Handle case where expand_mult does
	require/generate any instructions (i.e. multiplication by zero).

From-SVN: r91851

3 files changed, 31 insertions, 6 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b74fcd8..b03f62a 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2004-12-07  Roger Sayle  <roger@eyesopen.com>
+
+	PR middle-end/18293
+	* expmed.c (EXACT_POWER_OF_2_OR_ZERO_P): Move definition earlier.
+	(expand_mult): Special case powers of two to avoid synth_mult.
+	* loop.c (product_cheap_p): Handle case where expand_mult does
+	require/generate any instructions (i.e. multiplication by zero).
+
 2004-12-07  Richard Henderson  <rth@redhat.com>
 
 	* tree-pretty-print.c (dump_array_domain): Split out from
diff --git a/gcc/expmed.c b/gcc/expmed.c
index c6c8058..47fc2d2 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -54,6 +54,9 @@ static void do_cmp_and_jump (rtx, rtx, enum rtx_code, enum machine_mode, rtx);
 static rtx expand_smod_pow2 (enum machine_mode, rtx, HOST_WIDE_INT);
 static rtx expand_sdiv_pow2 (enum machine_mode, rtx, HOST_WIDE_INT);
 
+/* Test whether a value is zero of a power of two.  */
+#define EXACT_POWER_OF_2_OR_ZERO_P(x) (((x) & ((x) - 1)) == 0)
+
 /* Nonzero means divides or modulus operations are relatively cheap for
    powers of two, so don't use branches; emit the operation instead.
    Usually, this will mean that the MD file will emit non-branch
@@ -3024,11 +3027,25 @@ expand_mult (enum machine_mode mode, rtx op0, rtx op1, rtx target,
   if (const_op1 && GET_CODE (const_op1) == CONST_INT
       && (unsignedp || !flag_trapv))
     {
-      int mult_cost = rtx_cost (gen_rtx_MULT (mode, op0, op1), SET);
+      HOST_WIDE_INT coeff = INTVAL (const_op1);
+      int mult_cost;
+
+      /* Special case powers of two.  */
+      if (EXACT_POWER_OF_2_OR_ZERO_P (coeff))
+	{
+	  if (coeff == 0)
+	    return const0_rtx;
+	  if (coeff == 1)
+	    return op0;
+	  return expand_shift (LSHIFT_EXPR, mode, op0,
+			       build_int_cst (NULL_TREE, floor_log2 (coeff)),
+			       target, unsignedp);
+	}
 
-      if (choose_mult_variant (mode, INTVAL (const_op1), &algorithm, &variant,
+      mult_cost = rtx_cost (gen_rtx_MULT (mode, op0, op1), SET);
+      if (choose_mult_variant (mode, coeff, &algorithm, &variant,
 			       mult_cost))
-	return expand_mult_const (mode, op0, INTVAL (const_op1), target,
+	return expand_mult_const (mode, op0, coeff, target,
 				  &algorithm, variant);
     }
 
@@ -3627,8 +3644,6 @@ expand_sdiv_pow2 (enum machine_mode mode, rtx op0, HOST_WIDE_INT d)
    (x mod 12) == (((x & 1023) + ((x >> 8) & ~3)) * 0x15555558 >> 2 * 3) >> 28
    */
 
-#define EXACT_POWER_OF_2_OR_ZERO_P(x) (((x) & ((x) - 1)) == 0)
-
 rtx
 expand_divmod (int rem_flag, enum tree_code code, enum machine_mode mode,
 	       rtx op0, rtx op1, rtx target, int unsignedp)
diff --git a/gcc/loop.c b/gcc/loop.c
index 995df48..15039e8 100644
--- a/gcc/loop.c
+++ b/gcc/loop.c
@@ -9202,7 +9202,9 @@ product_cheap_p (rtx a, rtx b)
   end_sequence ();
 
   win = 1;
-  if (INSN_P (tmp))
+  if (tmp == NULL_RTX)
+    ;
+  else if (INSN_P (tmp))
     {
       n_insns = 0;
       while (tmp != NULL_RTX)