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

[paulo@matos-sorge.com]

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

--- Comment #4 from Paulo J. Matos <paulo@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.