Re: [PATCH (7/7)] Mixed-sign multiplies using narrowest mode

[Andrew Stubbs <ams at codesourcery dot com>]

On 28/06/11 17:23, Andrew Stubbs wrote:
> On 23/06/11 15:43, Andrew Stubbs wrote:
> > Patch 4 introduced support for using signed multiplies to code unsigned
> > multiplies in a narrower mode. Patch 5 then introduced support for
> > mis-matched input modes.
> >
> > These two combined mean that there is case where only the smaller of two
> > inputs is unsigned, and yet it still tries to user a mode wider than the
> > larger, signed input. This is bad because it means unnecessary extends
> > and because the wider operation might not exist.
> >
> > This patch catches that case, and ensures that the smaller, unsigned
> > input, is zero-extended to match the mode of the larger, signed input.
> >
> > Of course, both inputs may still have to be extended to fit the nearest
> > available instruction, so it doesn't make a difference every time.
> >
> > OK?
>
> This update fixes Janis' issue with the testsuite.

And this version is updated to fit the changes made earlier in the 
series, and also to use the precision, instead of the mode-size, in 
order to better optimize bitfields.

OK?

Andrew
2011-06-24  Andrew Stubbs  <ams@codesourcery.com>

	gcc/
	* tree-ssa-math-opts.c (convert_mult_to_widen): Better handle
	unsigned inputs of different modes.
	(convert_plusminus_to_widen): Likewise.

	gcc/testsuite/
	* gcc.target/arm/wmul-9.c: New file.
	* gcc.target/arm/wmul-bitfield-2.c: New file.

--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/wmul-9.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=armv7-a" } */
+
+long long
+foo (long long a, short *b, char *c)
+{
+  return a + *b * *c;
+}
+
+/* { dg-final { scan-assembler "smlalbb" } } */
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/wmul-bitfield-2.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=armv7-a" } */
+
+struct bf
+{
+  int a : 3;
+  unsigned int b : 15;
+  int c : 3;
+};
+
+long long
+foo (long long a, struct bf b, struct bf c)
+{
+  return a + b.b * c.c;
+}
+
+/* { dg-final { scan-assembler "smlalbb" } } */
--- a/gcc/tree-ssa-math-opts.c
+++ b/gcc/tree-ssa-math-opts.c
@@ -2121,9 +2121,18 @@ convert_mult_to_widen (gimple stmt, gimple_stmt_iterator *gsi)
     {
       if (op != smul_widen_optab)
 	{
-	  from_mode = GET_MODE_WIDER_MODE (from_mode);
-	  if (GET_MODE_SIZE (to_mode) <= GET_MODE_SIZE (from_mode))
-	    return false;
+	  /* We can use a signed multiply with unsigned types as long as
+	     there is a wider mode to use, or it is the smaller of the two
+	     types that is unsigned.  Note that type1 >= type2, always.  */
+	  if ((TYPE_UNSIGNED (type1)
+	       && TYPE_PRECISION (type1) == GET_MODE_PRECISION (from_mode))
+	      || (TYPE_UNSIGNED (type2)
+		  && TYPE_PRECISION (type2) == GET_MODE_PRECISION (from_mode)))
+	    {
+	      from_mode = GET_MODE_WIDER_MODE (from_mode);
+	      if (GET_MODE_SIZE (to_mode) <= GET_MODE_SIZE (from_mode))
+		return false;
+	    }
 
 	  op = smul_widen_optab;
 	  handler = find_widening_optab_handler_and_mode (op, to_mode,
@@ -2290,14 +2299,20 @@ convert_plusminus_to_widen (gimple_stmt_iterator *gsi, gimple stmt,
   /* There's no such thing as a mixed sign madd yet, so use a wider mode.  */
   if (from_unsigned1 != from_unsigned2)
     {
-      enum machine_mode mode = GET_MODE_WIDER_MODE (from_mode);
-      if (GET_MODE_PRECISION (mode) < GET_MODE_PRECISION (to_mode))
+      /* We can use a signed multiply with unsigned types as long as
+	 there is a wider mode to use, or it is the smaller of the two
+	 types that is unsigned.  Note that type1 >= type2, always.  */
+      if ((from_unsigned1
+	   && TYPE_PRECISION (type1) == GET_MODE_PRECISION (from_mode))
+	  || (from_unsigned2
+	      && TYPE_PRECISION (type2) == GET_MODE_PRECISION (from_mode)))
 	{
-	  from_mode = mode;
-	  from_unsigned1 = from_unsigned2 = false;
+	  from_mode = GET_MODE_WIDER_MODE (from_mode);
+	  if (GET_MODE_SIZE (from_mode) >= GET_MODE_SIZE (to_mode))
+	    return false;
 	}
-      else
-	return false;
+
+      from_unsigned1 = from_unsigned2 = false;
     }
 
   /* If there was a conversion between the multiply and addition