[Bug fortran/53642] Front-end optimization: Wrong string length for deferred-length strings

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53642

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |burnus at gcc dot gnu.org

--- Comment #1 from Tobias Burnus <burnus at gcc dot gnu.org> 2012-06-12 15:52:34 UTC ---
I was thinking about the following patch - namely, doing in optimize_assignment
the remove_trim only if "!lhs->ts.deferred".

 * * *

However, that does not work; seemingly,  a = trim(b) is replaced by
   a = b(1:len_trim(b))  in such a way, that  len(a) == 0  instead of 3.

The same issue occurs for a manual:
   trimmed = string(1:len_trim(string))

Thus, the follow-up issue is not a FE optimization issue but rather a trans*.c
issue. The generated code is [some casting removed]:

        trimmed = __builtin_malloc (MAX_EXPR <NON_LVALUE_EXPR <D.1861>, 0>);

        .trimmed = MAX_EXPR <NON_LVALUE_EXPR <D.1861>, 0>;

        D.1861 = _gfortran_string_len_trim (4, &string);

Which shows the wrong ordering, similar to bug 45170 comment 34, which is fixed
by the patch at bug 45170 comment 34. That patch also solves the len_trim issue
above.


--- a/gcc/fortran/frontend-passes.c
+++ b/gcc/fortran/frontend-passes.c
@@ -738 +738 @@ optimize_assignment (gfc_code * c)
-  if (lhs->ts.type == BT_CHARACTER)
+  if (lhs->ts.type == BT_CHARACTER && !lhs->ts.deferred)
@@ -740 +740 @@ optimize_assignment (gfc_code * c)
-      /* Optimize away a = trim(b), where a is a character variable.  */
+      /* Optimize  a = trim(b)  to  a = b.  */
@@ -743,4 +743,2 @@ optimize_assignment (gfc_code * c)
-      /* Replace a = '   ' by a = '' to optimize away a memcpy, but only
-        for strings with non-deferred length (otherwise we would
-        reallocate the length.  */
-      if (empty_string(rhs) && ! lhs->ts.deferred)
+      /* Replace a = '   ' by a = '' to optimize away a memcpy.  */
+      if (empty_string(rhs))
@@ -1174 +1172 @@ optimize_trim (gfc_expr *e)
-  /* Build the function call to len_trim(x, gfc_defaul_integer_kind).  */
+  /* Build the function call to len_trim(x, gfc_default_integer_kind).  */