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Fix stack overflow problem when bootstrapping on Darwin
- From: Geoffrey Keating <gkeating at apple dot com>
- To: gcc-patches at gcc dot gnu dot org
- Date: Tue, 29 Apr 2003 13:38:56 -0700 (PDT)
- Subject: Fix stack overflow problem when bootstrapping on Darwin
If you have a long chain of code like:
...
goto L20;
L1: ...
goto L21;
L2: ...
then what happens is that expand_stmt, when it hits each 'goto', calls
expand_unreachable_stmt, which promptly notices the label, which calls
back to expand_stmt. After this happens a few thousand times, as in
insn-recog.c, the stack overflows. Some of these would be sibcalls,
which would help a lot, except that the stage1 compiler is built using
-O0 and so not only are there no sibcalls but the stack frames are
unusually inflated.
So, this rearranges expand_unreachable_stmt so that it's usually just
a subroutine of expand_stmt; it processes only the unreachable insns,
and then returns to let expand_stmt finish up.
I don't think this is necessary for 3.3 since it happens only while
bootstrapping and 3.4 has a significantly more complicated insn-recog.c.
Bootstrapped & tested on powerpc-darwin.
--
- Geoffrey Keating <geoffk@apple.com>
===File ~/patches/gcc-unreachablestkoverflow.patch==========
2003-04-29 Geoffrey Keating <geoffk@apple.com>
* c-semantics.c (expand_unreachable_stmt): Return a tree.
(expand_stmt): Update for change to expand_unreachable_stmt.
(expand_unreachable_if_stmt): Likewise.
Index: c-semantics.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-semantics.c,v
retrieving revision 1.55
diff -u -p -u -p -r1.55 c-semantics.c
--- c-semantics.c 20 Apr 2003 22:58:28 -0000 1.55
+++ c-semantics.c 29 Apr 2003 20:36:59 -0000
@@ -55,7 +55,7 @@ void (*lang_expand_decl_stmt) PARAMS ((t
static tree find_reachable_label_1 PARAMS ((tree *, int *, void *));
static tree find_reachable_label PARAMS ((tree));
static bool expand_unreachable_if_stmt PARAMS ((tree));
-static bool expand_unreachable_stmt PARAMS ((tree, int));
+static tree expand_unreachable_stmt PARAMS ((tree, int));
/* Create an empty statement tree rooted at T. */
@@ -823,8 +823,8 @@ expand_stmt (t)
case RETURN_STMT:
genrtl_return_stmt (t);
- expand_unreachable_stmt (TREE_CHAIN (t), warn_notreached);
- return;
+ t = expand_unreachable_stmt (TREE_CHAIN (t), warn_notreached);
+ goto process_t;
case EXPR_STMT:
genrtl_expr_stmt_value (EXPR_STMT_EXPR (t), TREE_ADDRESSABLE (t),
@@ -859,13 +859,13 @@ expand_stmt (t)
case BREAK_STMT:
genrtl_break_stmt ();
- expand_unreachable_stmt (TREE_CHAIN (t), warn_notreached);
- return;
+ t = expand_unreachable_stmt (TREE_CHAIN (t), warn_notreached);
+ goto process_t;
case CONTINUE_STMT:
genrtl_continue_stmt ();
- expand_unreachable_stmt (TREE_CHAIN (t), warn_notreached);
- return;
+ t = expand_unreachable_stmt (TREE_CHAIN (t), warn_notreached);
+ goto process_t;
case SWITCH_STMT:
genrtl_switch_stmt (t);
@@ -890,8 +890,8 @@ expand_stmt (t)
NOTE_PREDICTION (note) = NOTE_PREDICT (PRED_GOTO, NOT_TAKEN);
}
genrtl_goto_stmt (GOTO_DESTINATION (t));
- expand_unreachable_stmt (TREE_CHAIN (t), warn_notreached);
- return;
+ t = expand_unreachable_stmt (TREE_CHAIN (t), warn_notreached);
+ goto process_t;
case ASM_STMT:
genrtl_asm_stmt (ASM_CV_QUAL (t), ASM_STRING (t),
@@ -915,12 +915,13 @@ expand_stmt (t)
break;
}
+ /* Go on to the next statement in this scope. */
+ t = TREE_CHAIN (t);
+
+ process_t:
/* Restore saved state. */
current_stmt_tree ()->stmts_are_full_exprs_p
= saved_stmts_are_full_exprs_p;
-
- /* Go on to the next statement in this scope. */
- t = TREE_CHAIN (t);
}
}
@@ -964,6 +965,8 @@ static bool
expand_unreachable_if_stmt (t)
tree t;
{
+ tree n;
+
if (find_reachable_label (IF_COND (t)) != NULL_TREE)
{
genrtl_if_stmt (t);
@@ -972,31 +975,38 @@ expand_unreachable_if_stmt (t)
if (THEN_CLAUSE (t) && ELSE_CLAUSE (t))
{
- if (expand_unreachable_stmt (THEN_CLAUSE (t), 0))
+ n = expand_unreachable_stmt (THEN_CLAUSE (t), 0);
+
+ if (n != NULL_TREE)
{
rtx label;
+ expand_stmt (n);
label = gen_label_rtx ();
emit_jump (label);
- expand_unreachable_stmt (ELSE_CLAUSE (t), 0);
+ expand_stmt (expand_unreachable_stmt (ELSE_CLAUSE (t), 0));
emit_label (label);
return true;
}
else
- return expand_unreachable_stmt (ELSE_CLAUSE (t), 0);
+ n = expand_unreachable_stmt (ELSE_CLAUSE (t), 0);
}
else if (THEN_CLAUSE (t))
- return expand_unreachable_stmt (THEN_CLAUSE (t), 0);
+ n = expand_unreachable_stmt (THEN_CLAUSE (t), 0);
else if (ELSE_CLAUSE (t))
- return expand_unreachable_stmt (ELSE_CLAUSE (t), 0);
-
- return false;
+ n = expand_unreachable_stmt (ELSE_CLAUSE (t), 0);
+ else
+ n = NULL_TREE;
+
+ expand_stmt (n);
+
+ return n != NULL_TREE;
}
/* Expand an unreachable statement list. This function skips all
statements preceding the first potentially reachable label and
- then expands the statements normally with expand_stmt. This
- function returns true if such a reachable label was found. */
-static bool
+ then returns the label (or, in same cases, the statement after
+ one containing the label). */
+static tree
expand_unreachable_stmt (t, warn)
tree t;
int warn;
@@ -1037,36 +1047,31 @@ expand_unreachable_stmt (t, warn)
case RETURN_STMT:
if (find_reachable_label (RETURN_STMT_EXPR (t)) != NULL_TREE)
- {
- expand_stmt (t);
- return true;
- }
+ return t;
break;
case EXPR_STMT:
if (find_reachable_label (EXPR_STMT_EXPR (t)) != NULL_TREE)
- {
- expand_stmt (t);
- return true;
- }
+ return t;
break;
case IF_STMT:
if (expand_unreachable_if_stmt (t))
- {
- expand_stmt (TREE_CHAIN (t));
- return true;
- }
+ return TREE_CHAIN (t);
break;
case COMPOUND_STMT:
- if (expand_unreachable_stmt (COMPOUND_BODY (t), warn))
- {
- expand_stmt (TREE_CHAIN (t));
- return true;
- }
- warn = false;
- break;
+ {
+ tree n;
+ n = expand_unreachable_stmt (COMPOUND_BODY (t), warn);
+ if (n != NULL_TREE)
+ {
+ expand_stmt (n);
+ return TREE_CHAIN (t);
+ }
+ warn = false;
+ break;
+ }
case SCOPE_STMT:
saved = stmts_are_full_exprs_p ();
@@ -1076,11 +1081,10 @@ expand_unreachable_stmt (t, warn)
break;
default:
- expand_stmt (t);
- return true;
+ return t;
}
t = TREE_CHAIN (t);
}
- return false;
+ return NULL_TREE;
}
============================================================