exceptions and cross jump optimization

[ulrich dot kunitz at db dot com]

Following programm gives different output if compiled with -O0 or -O1.

/* cross jump optimization bug */

#include <stdio.h>
#include <string.h>

class A {
public:
    virtual void throw_exception();
    void xxx(char * sz);
};

void A::throw_exception() { throw 1; }

void A::xxx(char * sz) {
    if (strcmp(sz, "xxx") == 0) {
        try {
            throw_exception();
            return;
        }
        catch (int n) { }
    }
    else {
        throw_exception();
        return;
    }
}

int  main(void) {
    A a;
    int fOk = 1;
    try {
        a.xxx("xxx");
    }
    catch (int n) {
        fOk = 0;
    }
    printf(fOk != 0 ? "Ok\n" : "Wrong\n");
}

Following patch proves that this is cross jump optimization problem:

--- gcc/jump.c.orig     Sun May 31 22:18:18 1998
+++ gcc/jump.c  Mon Jun  1 02:11:30 1998
@@ -148,6 +148,8 @@
   int max_uid = 0;
   rtx last_insn;

+  /* Following code line switches cross jump optimization off. */
+  cross_jump = 0;
   cross_jump_death_matters = (cross_jump == 2);

I've been discussing the problem with Martin Loewis
(martin@mira.isdn.cs.tu-berlin.de).
He didn't like to use in_same_eh_region() in find_cross_jump() because the
function
returns always false in the first optimizer passes. Jump cross
optimizations isn't done in
that passes, so maybe it isn't such a bad idea.

Ciao,  Uli Kunitz