combine.c (find_split_point): Undo canonicalization of multiply-add to (minus x (mult)) when...

	* combine.c (find_split_point): Undo canonicalization of multiply-add
	to (minus x (mult)) when it seems likely that this will increase the
	chances of a split.

	* gcc.target/i386/combine-mul.c: New test.

From-SVN: r163547

gcc/ChangeLog

@@ -4,6 +4,10 @@
 	* combine.c (try_combine): Use reg_overlap_mentioned_p rather than
 	dead_or_set_p when computing i0_feeds_i2_n.
 
+	* combine.c (find_split_point): Undo canonicalization of multiply-add
+	to (minus x (mult)) when it seems likely that this will increase the
+	chances of a split.
+
 2010-08-25  Richard Guenther  <rguenther@suse.de>
 
 	PR lto/44562

gcc/combine.c

@@ -4771,6 +4771,23 @@ find_split_point (rtx *loc, rtx insn, bool set_src)
 
     case PLUS:
     case MINUS:
+      /* Canonicalization can produce (minus A (mult B C)), where C is a
+	 constant.  It may be better to try splitting (plus (mult B -C) A)
+	 instead if this isn't a multiply by a power of two.  */
+      if (set_src && code == MINUS && GET_CODE (XEXP (x, 1)) == MULT
+	  && GET_CODE (XEXP (XEXP (x, 1), 1)) == CONST_INT
+	  && exact_log2 (INTVAL (XEXP (XEXP (x, 1), 1))) < 0)
+	{
+	  enum machine_mode mode = GET_MODE (x);
+	  unsigned HOST_WIDE_INT this_int = INTVAL (XEXP (XEXP (x, 1), 1));
+	  HOST_WIDE_INT other_int = trunc_int_for_mode (-this_int, mode);
+	  SUBST (*loc, gen_rtx_PLUS (mode, gen_rtx_MULT (mode,
+							 XEXP (XEXP (x, 1), 0),
+							 GEN_INT (other_int)),
+				     XEXP (x, 0)));
+	  return find_split_point (loc, insn, set_src);
+	}
+
       /* Split at a multiply-accumulate instruction.  However if this is
          the SET_SRC, we likely do not have such an instruction and it's
          worthless to try this split.  */

gcc/testsuite/ChangeLog

+2010-08-25  Bernd Schmidt  <bernds@codesourcery.com>
+
+	* gcc.target/i386/combine-mul.c: New test.
+
 2010-08-25  Richard Guenther  <rguenther@suse.de>
 
 	PR lto/44562

gcc/testsuite/gcc.target/i386/combine-mul.c

+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-final { scan-assembler-not "12345" } } */
+
+static inline unsigned int myrnd (void)
+{
+    static unsigned int s = 1388815473;
+    s *= 1103515245;
+    s += 12345;
+}
+
+struct __attribute__ ((packed)) A {
+    unsigned short i:1, l:1, j:3, k:11;
+};
+
+struct A sA;
+void testA (void)
+{
+    char *p = (char *) &sA;
+    *p++ = myrnd ();
+    *p++ = myrnd ();
+    sA.k = -1;
+}