[Bug tree-optimization/55761] process_assignment assumes -1 can be created

[pa...@matos-sorge.com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55761



--- Comment #4 from Paulo J. Matos <pa...@matos-sorge.com> 2012-12-20 16:58:08 
UTC ---

I created a new patch from your comment to gcc-patches:

diff --git a/gcc/tree-tailcall.c b/gcc/tree-tailcall.c

index 5b1fd2b..8c7d142 100644

--- a/gcc/tree-tailcall.c

+++ b/gcc/tree-tailcall.c

@@ -326,26 +326,14 @@ process_assignment (gimple stmt, gimple_stmt_iterator

call

       return true;



     case NEGATE_EXPR:

-      if (FLOAT_TYPE_P (TREE_TYPE (op0)))

-        *m = build_real (TREE_TYPE (op0), dconstm1);

-      else

-        *m = build_int_cst (TREE_TYPE (op0), -1);

-

+      *m = fold_unary (NEGATE_EXPR, TREE_TYPE (op0), op0);

       *ass_var = dest;

       return true;



     case MINUS_EXPR:

-      if (*ass_var == op0)

-        *a = fold_build1 (NEGATE_EXPR, TREE_TYPE (non_ass_var), non_ass_var);

-      else

-        {

-          if (FLOAT_TYPE_P (TREE_TYPE (non_ass_var)))

-            *m = build_real (TREE_TYPE (non_ass_var), dconstm1);

-          else

-            *m = build_int_cst (TREE_TYPE (non_ass_var), -1);

-

-          *a = fold_build1 (NEGATE_EXPR, TREE_TYPE (non_ass_var),

non_ass_var);

-        }

+        *a = fold_unary (NEGATE_EXPR, TREE_TYPE (non_ass_var), non_ass_var);

+      if (*ass_var == op1)

+        *m = fold_unary (NEGATE_EXPR, TREE_TYPE (non_ass_var), non_ass_var);



       *ass_var = dest;

       return true;





However, I am less confident that it works now. Mainly because of the *m in

MINUS_EXPR. It seems from the comments in tailcall structure that m should be

-1, not (NEGATE non_ass_var). However, we cannot really create a -1 for vectors

straightforwardly.



I guess that, as per your comment below, we would need a build_minus_one_cst

that handles not only scalar types but also vector types.