Re: Extend widening_mul pass to handle fixed-point types

[Richard Sandiford <rdsandiford@googlemail.com>]

Ramana Radhakrishnan <ramana.radhakrishnan@arm.com> writes:
> Hmmm there are regressions after my patch was applied. I had to do some
> rebuilds because trunk appears to be broken for other reasons at the
> minute for ARM which I shall investigate next. 

Yeah, I think it's the other way about: expand_widen_pattern_expr
is using the right type and convert_plusminus_to_widen is using
the wrong one.  The type we pass to optab_for_tree_code determines
the _sign_ of the multiplication, not the size, so we want to pass
in the unwidened type.

> We weren't generating any widening operations before this patch (and I
> suspect my 2 patches are just for fixing the ICE's and doing the right
> thing). If it were just adding support for fixed point arithmetic then
> this is just broken because it shouldn't have changed the way in  which
> code was generated for normal integer operations.  

For the record, the patch wasn't just about adding fixed-point support.
It was also about allowing multiply-accumulate to be used where no plain
multiplication exists.  So the problem for ARM was that the use of the
wrong type in convert_plusminus_to_widen was being hidden by the use of
the right type in convert_mult_widen (i.e. the patch exposed a latent bug).

Could you give the attached patch a try?  It also fixes a case where
the code could create mixed sign-and-unsigned maccs (a bug that existed
before my patch) and a botched call to is_widening_mult_p (a bug
introduced by my patch, sorry).

Richard


gcc/
	* tree-ssa-math-opts.c (convert_plusminus_to_widen): Fix type
	used in the call to optab_for_tree_code.  Fix the second
	is_widening_mult_p call.  Check that both unwidened operands
	have the same sign.

Index: gcc/tree-ssa-math-opts.c
===================================================================
--- gcc/tree-ssa-math-opts.c	2010-07-28 21:09:59.000000000 +0100
+++ gcc/tree-ssa-math-opts.c	2010-07-28 21:10:00.000000000 +0100
@@ -1414,13 +1414,6 @@ convert_plusminus_to_widen (gimple_stmt_
   else
     wmult_code = WIDEN_MULT_PLUS_EXPR;
 
-  /* Verify that the machine can perform a widening multiply
-     accumulate in this mode/signedness combination, otherwise
-     this transformation is likely to pessimize code.  */
-  this_optab = optab_for_tree_code (wmult_code, type, optab_default);
-  if (optab_handler (this_optab, TYPE_MODE (type)) == CODE_FOR_nothing)
-    return false;
-
   rhs1 = gimple_assign_rhs1 (stmt);
   rhs2 = gimple_assign_rhs2 (stmt);
 
@@ -1447,37 +1440,49 @@ convert_plusminus_to_widen (gimple_stmt_
       if (!is_widening_mult_p (rhs1_stmt, &type1, &mult_rhs1,
 			       &type2, &mult_rhs2))
 	return false;
-      mult_rhs1 = fold_convert (type1, mult_rhs1);
-      mult_rhs2 = fold_convert (type2, mult_rhs2);
       add_rhs = rhs2;
     }
   else if (rhs2_code == MULT_EXPR)
     {
-      if (!is_widening_mult_p (rhs1_stmt, &type1, &mult_rhs1,
+      if (!is_widening_mult_p (rhs2_stmt, &type1, &mult_rhs1,
 			       &type2, &mult_rhs2))
 	return false;
-      mult_rhs1 = fold_convert (type1, mult_rhs1);
-      mult_rhs2 = fold_convert (type2, mult_rhs2);
       add_rhs = rhs1;
     }
   else if (code == PLUS_EXPR && rhs1_code == WIDEN_MULT_EXPR)
     {
       mult_rhs1 = gimple_assign_rhs1 (rhs1_stmt);
       mult_rhs2 = gimple_assign_rhs2 (rhs1_stmt);
+      type1 = TREE_TYPE (mult_rhs1);
+      type2 = TREE_TYPE (mult_rhs2);
       add_rhs = rhs2;
     }
   else if (rhs2_code == WIDEN_MULT_EXPR)
     {
       mult_rhs1 = gimple_assign_rhs1 (rhs2_stmt);
       mult_rhs2 = gimple_assign_rhs2 (rhs2_stmt);
+      type1 = TREE_TYPE (mult_rhs1);
+      type2 = TREE_TYPE (mult_rhs2);
       add_rhs = rhs1;
     }
   else
     return false;
 
+  if (TYPE_UNSIGNED (type1) != TYPE_UNSIGNED (type2))
+    return false;
+
+  /* Verify that the machine can perform a widening multiply
+     accumulate in this mode/signedness combination, otherwise
+     this transformation is likely to pessimize code.  */
+  this_optab = optab_for_tree_code (wmult_code, type1, optab_default);
+  if (optab_handler (this_optab, TYPE_MODE (type)) == CODE_FOR_nothing)
+    return false;
+
   /* ??? May need some type verification here?  */
 
-  gimple_assign_set_rhs_with_ops_1 (gsi, wmult_code, mult_rhs1, mult_rhs2,
+  gimple_assign_set_rhs_with_ops_1 (gsi, wmult_code,
+				    fold_convert (type1, mult_rhs1),
+				    fold_convert (type2, mult_rhs2),
 				    add_rhs);
   update_stmt (gsi_stmt (*gsi));
   return true;