[gfortran] Fix PR 20361: Check if equivalence fits on stack

[Tobias Schlüter <tobias dot schlueter at physik dot uni-muenchen dot de>]

We didn't check if an equivalence actually fits on the stack when building it,
so big equivalences caused segfaults.  This patch fixes it, fairly trivial,
the only change whose reason is non-obvious is that I'm now giving the union
an identifier.  This is required, because making the union TREE_STATIC gives
the compiler a reason to actually look at its name.

Bubblestrapped and regtested, I also verified that the assembly output
correctly changes for different values of -fmax-stack-var-size.  Is a testcase
which scans the assembler output preferred, or is a testcase which uses a huge
array enough?  Ok?

- Tobi

2005-03-12  Tobias Schl"uter  <tobias.schlueter@physik.uni-muenchen.de>

        PR fortran/20361
        * trans-array.c (gfc_stack_space_left): Remove unused variable.
        (gfc_can_put_var_on_stack): Move to trans-decl.c, remove #if 0'ed
	code.
        * trans-array.h (gfc_stack_space_left, gfc_can_put_var_on_stack):
        Remove declaration / prototype.
	* trans-common.c (build_equiv_decl): Give union a name.  Check if
	it can be put on the stack.
        * trans-decl.c (gfc_stack_space_left): Move function here.
        (gfc_build_qualified_array): Fix comment typo.
        * trans.h (gfc_put_var_on_stack): Add prototype.

Index: trans-array.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/fortran/trans-array.c,v
retrieving revision 1.39
diff -u -p -r1.39 trans-array.c
--- trans-array.c	24 Feb 2005 21:59:24 -0000	1.39
+++ trans-array.c	12 Mar 2005 14:55:11 -0000
@@ -99,43 +99,6 @@ static gfc_ss *gfc_walk_subexpr (gfc_ss 
 static gfc_ss gfc_ss_terminator_var;
 gfc_ss * const gfc_ss_terminator = &gfc_ss_terminator_var;
 
-unsigned HOST_WIDE_INT gfc_stack_space_left;
-
-
-/* Returns true if a variable of specified size should go on the stack.  */
-
-int
-gfc_can_put_var_on_stack (tree size)
-{
-  unsigned HOST_WIDE_INT low;
-
-  if (!INTEGER_CST_P (size))
-    return 0;
-
-  if (gfc_option.flag_max_stack_var_size < 0)
-    return 1;
-
-  if (TREE_INT_CST_HIGH (size) != 0)
-    return 0;
-
-  low = TREE_INT_CST_LOW (size);
-  if (low > (unsigned HOST_WIDE_INT) gfc_option.flag_max_stack_var_size)
-    return 0;
-
-/* TODO: Set a per-function stack size limit.  */
-#if 0
-  /* We should be a bit more clever with array temps.  */
-  if (gfc_option.flag_max_function_vars_size >= 0)
-    {
-      if (low > gfc_stack_space_left)
-	return 0;
-
-      gfc_stack_space_left -= low;
-    }
-#endif
-
-  return 1;
-}
 
 static tree
 gfc_array_dataptr_type (tree desc)
Index: trans-array.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/fortran/trans-array.h,v
retrieving revision 1.7
diff -u -p -r1.7 trans-array.h
--- trans-array.h	8 Nov 2004 14:56:40 -0000	1.7
+++ trans-array.h	12 Mar 2005 14:55:11 -0000
@@ -95,11 +95,6 @@ tree gfc_conv_array_stride (tree, int);
 tree gfc_conv_array_lbound (tree, int);
 tree gfc_conv_array_ubound (tree, int);
 
-/* The remaining space available for stack variables.  */
-extern unsigned HOST_WIDE_INT gfc_stack_space_left;
-/* Returns true if a variable of specified size should go on the stack.  */
-int gfc_can_put_var_on_stack (tree);
-
 /* Build expressions for accessing components of an array descriptor.  */
 tree gfc_conv_descriptor_data (tree);
 tree gfc_conv_descriptor_offset (tree);
Index: trans-common.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/fortran/trans-common.c,v
retrieving revision 1.23
diff -u -p -r1.23 trans-common.c
--- trans-common.c	23 Feb 2005 19:02:14 -0000	1.23
+++ trans-common.c	12 Mar 2005 14:55:11 -0000
@@ -260,10 +260,11 @@ build_equiv_decl (tree union_type, bool 
       return decl;
     }
 
-  decl = build_decl (VAR_DECL, NULL, union_type);
+  decl = build_decl (VAR_DECL, get_identifier ("equiv"), union_type);
   DECL_ARTIFICIAL (decl) = 1;
 
-  DECL_COMMON (decl) = 1;
+  if (!gfc_can_put_var_on_stack (DECL_SIZE_UNIT (decl)))
+      TREE_STATIC (decl) = 1;
 
   TREE_ADDRESSABLE (decl) = 1;
   TREE_USED (decl) = 1;
Index: trans-decl.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/fortran/trans-decl.c,v
retrieving revision 1.54
diff -u -p -r1.54 trans-decl.c
--- trans-decl.c	24 Feb 2005 18:26:27 -0000	1.54
+++ trans-decl.c	12 Mar 2005 14:55:12 -0000
@@ -317,6 +317,32 @@ gfc_sym_mangled_function_id (gfc_symbol 
 }
 
 
+/* Returns true if a variable of specified size should go on the stack.  */
+
+int
+gfc_can_put_var_on_stack (tree size)
+{
+  unsigned HOST_WIDE_INT low;
+
+  if (!INTEGER_CST_P (size))
+    return 0;
+
+  if (gfc_option.flag_max_stack_var_size < 0)
+    return 1;
+
+  if (TREE_INT_CST_HIGH (size) != 0)
+    return 0;
+
+  low = TREE_INT_CST_LOW (size);
+  if (low > (unsigned HOST_WIDE_INT) gfc_option.flag_max_stack_var_size)
+    return 0;
+
+/* TODO: Set a per-function stack size limit.  */
+
+  return 1;
+}
+
+
 /* Finish processing of a declaration and install its initial value.  */
 
 static void
@@ -533,7 +559,7 @@ gfc_build_qualified_array (tree decl, gf
 
 
 /* For some dummy arguments we don't use the actual argument directly.
-   Instead we create a local decl and use that.  This allows us to preform
+   Instead we create a local decl and use that.  This allows us to perform
    initialization, and construct full type information.  */
 
 static tree
Index: trans.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/fortran/trans.h,v
retrieving revision 1.23
diff -u -p -r1.23 trans.h
--- trans.h	24 Feb 2005 21:59:24 -0000	1.23
+++ trans.h	12 Mar 2005 14:55:12 -0000
@@ -391,6 +391,9 @@ void gfc_shadow_sym (gfc_symbol *, tree,
 /* Restore the original variable.  */
 void gfc_restore_sym (gfc_symbol *, gfc_saved_var *);
 
+/* Returns true if a variable of specified size should go on the stack.  */
+int gfc_can_put_var_on_stack (tree);
+
 /* Allocate the lang-spcific part of a decl node.  */
 void gfc_allocate_lang_decl (tree);