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[Patch] Java: Definite [Un]Assignment Issues
- From: Ranjit Mathew <rmathew at gmail dot com>
- To: java-patches at gcc dot gnu dot org
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Sun, 23 May 2004 20:40:07 +0530
- Subject: [Patch] Java: Definite [Un]Assignment Issues
Hi,
This patch represents my attempt at fixing some of the
problems we have with definite [un]assignment in Java (JLS 2
Chapter 16).
These problems are only exposed by the Jacks testsuite.
Background:
-----------
GCJ started showing 30 XPASSes and 5 FAILs with Jacks after the tree-ssa
merge. This was because we were no longer throwing away an if-else with
a constant boolean condition. I started off with an attempt to fix these
FAILs, but have stopped for the moment at the state represented by this
patch.
Summary:
--------
Before my patch there were 30 XPASSes and 5 FAILs with Jacks.
After my patch there are 47 XPASSes and 5 FAILs with Jacks.
Diagnostics:
------------
The remaining FAILs are:
16.2.9-definite-unassign-pass-3
16.2.10-definite-unassign-pass-3
16.2.11-definite-unassign-pass-3
16.2.8-final-3
16.2.8-final-4
The first three - 16.2.{9,10,11}-definite-unassign-pass-3 - existed before
my patch and represent our decision to simplify the handling of loops w.r.t.
definite [un]assignment. See the comment for the "case LOOP_EXPR" in
check_init() in java/check-init.c for reference. Unless we want to change
that decision, I recommend that we simply mark these as expected "failures".
The next two represent failures with final variables inside switch
statements that I simply did not have the enthusiasm or energy to
pursue. :-(
Details:
--------
The following are the needed details on the patch in the order
of appearance of the associated changes:
a. Surprisingly for me, we were not at all marking "blank final" local
variables that represent the entities for which the whole "definite
unassignment" brouhaha in JLS 2 Chapter 16 is about!
I define DECL_LOCAL_FINAL_IUD in java-tree.h that is similar to - in fact
the same as - DECL_FIELD_FINAL_IUD, that I use to mark final
local variables that are initialised in their declaration. This is
being done in declare_local_variables() in parse.y in my patch.
b. With the above in place, check_final_reassigned() in check-init.c had
to be changed to give an error if an assignment to a final variable is
done when it is either:
i) "blank final" and not definitely unassigned, or,
ii) initialised final and reassigned
in accordance with the JLS.
c. JLS 2 16.1.7 clarifies how boolean assignment expressions should behave
when true/false. We were not honouring that.
d. We have a minor optimisation that removes initialised local variables to
reduce the length of the bitstrings maintained in memory. However, we
were not taking care to remove only non-final local variables, as these
need to be tracked to check for reassignments.
Checked on i686-pc-linux-gnu with no libjava testsuite regressions and
Jacks affected as summarised above.
Questions:
----------
1. OK for mainline?
2. If "Yes" for the above, OK to update
"libjava/testsuite/libjava.jacks/jacks.xfail" appropriately?
Thanks,
Ranjit.
Index: ChangeLog
from Ranjit Mathew <rmathew@hotmail.com>
* java-tree.h (DECL_LOCAL_FINAL_IUD): New macro to test if a
local variable was initialised upon declaration.
* parse.y (declare_local_variables): Set DECL_LOCAL_FINAL_IUD if
variable was final and initialised upon declaration.
* check-init.c (check_final_reassigned): Give error only if a blank
final is not definitely unassigned or if an initialised final is
reassigned.
(check_bool_init): Respect JLS2 16.1.7 requirements for boolean
assignment expressions.
(check_init): Perform initialised-variable-removing-optimisation
only on non-final local variables.
Index: java-tree.h
===================================================================
--- java-tree.h 2004-05-23 17:33:35.000000000 +0530
+++ java-tree.h 2004-05-23 17:36:45.000000000 +0530
@@ -902,8 +902,8 @@ union lang_tree_node
/* Safely tests whether FIELD_INNER_ACCESS exists or not. */
#define FIELD_INNER_ACCESS_P(DECL) \
DECL_LANG_SPECIFIC (DECL) && FIELD_INNER_ACCESS (DECL)
-/* True if a final variable was initialized upon its declaration,
- or (if a field) in an initializer. Set after definite assignment. */
+/* True if a final field was initialized upon its declaration
+ or in an initializer. Set after definite assignment. */
#define DECL_FIELD_FINAL_IUD(NODE) (DECL_LANG_SPECIFIC (NODE)->u.v.final_iud)
/* The original WFL of a final variable. */
#define DECL_FIELD_FINAL_WFL(NODE) (DECL_LANG_SPECIFIC(NODE)->u.v.wfl)
@@ -911,6 +911,8 @@ union lang_tree_node
#define DECL_OWNER(NODE) (DECL_LANG_SPECIFIC(NODE)->u.v.owner)
/* True if NODE is a local variable final. */
#define LOCAL_FINAL_P(NODE) (DECL_LANG_SPECIFIC (NODE) && DECL_FINAL (NODE))
+/* True if a final local variable was initialized upon its declaration. */
+#define DECL_LOCAL_FINAL_IUD(NODE) (DECL_LANG_SPECIFIC (NODE)->u.v.final_iud)
/* True if NODE is a final field. */
#define FINAL_VARIABLE_P(NODE) (FIELD_FINAL (NODE) && !FIELD_STATIC (NODE))
/* True if NODE is a class final field. */
Index: parse.y
===================================================================
--- parse.y 2004-05-23 15:59:32.000000000 +0530
+++ parse.y 2004-05-23 17:37:35.000000000 +0530
@@ -7375,6 +7375,13 @@ declare_local_variables (int modifier, t
if (init && java_error_count)
init = NULL_TREE;
+ /* Remember it if this is an initialized-upon-declaration final
+ variable. */
+ if (init && final_p)
+ {
+ DECL_LOCAL_FINAL_IUD (decl) = 1;
+ }
+
/* Add the initialization function to the current function's code */
if (init)
{
Index: check-init.c
===================================================================
--- check-init.c 2004-05-21 21:14:10.000000000 +0530
+++ check-init.c 2004-05-23 20:17:03.000000000 +0530
@@ -210,7 +210,8 @@ check_final_reassigned (tree decl, words
assigned must be reported as errors */
if (DECL_FINAL (decl) && index != -2
&& (index < loop_current_locals /* I.e. -1, or outside current loop. */
- || ! UNASSIGNED_P (before, index)))
+ || (! DECL_LOCAL_FINAL_IUD (decl) && ! UNASSIGNED_P (before, index))
+ || (DECL_LOCAL_FINAL_IUD (decl) && ASSIGNED_P (before, index))))
{
final_assign_error (DECL_NAME (decl));
}
@@ -346,6 +347,8 @@ check_bool_init (tree exp, words before,
check_bool_init (TREE_OPERAND (exp, 1), before,
when_false, when_true);
check_final_reassigned (tmp, before);
+ INTERSECT (when_false, when_false, when_true);
+ COPY (when_true, when_false);
index = DECL_BIT_INDEX (tmp);
if (index >= 0)
{
@@ -531,6 +534,7 @@ check_init (tree exp, words before)
definitely assigned when once we checked the whole
function. */
if (! STATIC_CLASS_INIT_OPT_P () /* FIXME */
+ && ! DECL_FINAL (tmp)
&& index >= start_current_locals
&& index == num_current_locals - 1)
{