[gcjx] Tree-SSA Operands Processing Problem

[Ranjit Mathew <rmathew at gmail dot com>]

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Hi,

  While trying to debug a long-standing ICE on the
gcjx branch, I have found out that the root cause
of the problem is with the tree-ssa operands processing
code and it still seems to exist on the mainline
(as of revision 109471), though I have traced the code
path in a debugger and actually observed the problem only
on the gcjx branch.

In mainline, the code path starts from
tree-ssa-operands.c:1906 where we have a *local* variable
VAR whose address is passed on to add_stmt_operand() on
the next line:
- ----------------------- 8< -----------------------
   1903   /* Add a VUSE for each call-clobbered variable.  */
   1904   EXECUTE_IF_SET_IN_BITMAP (call_clobbered_vars, 0, u, bi)
   1905     {
   1906       tree var = referenced_var (u);
   1907       add_stmt_operand (&var, &empty_ann, opf_none |
opf_non_specific);
   1908     }
   1909
- ----------------------- 8< -----------------------

This function then passes this pointer to append_use() at
line 1634, which seems to just store it as-is in BUILD_USES:
- ----------------------- 8< -----------------------
   1572 static void
   1573 add_stmt_operand (tree *var_p, stmt_ann_t s_ann, int flags)
   1574 {
   [...]
   1628   if (is_real_op)
   1629     {
   1630       /* The variable is a GIMPLE register.  Add it to real
operands.  *        /
   1631       if (flags & opf_is_def)
   1632         append_def (var_p);
   1633       else
   1634         append_use (var_p);
   1635     }
- ----------------------- 8< -----------------------

This seems wrong.

I don't know whether this code path is actually ever
taken on mainline or why it hasn't caused any problems
yet, but on the gcjx branch it causes an ICE while
processing the method "of" of the inner class "UnicodeBlock"
of the class "java.lang.Character"
($GCC_SRC_DIR/libjava/java/lang/Character.java). Specifically,
it ICEs while processing the CALL_EXPR corresponding to
the call to _Jv_ThrowBadArrayIndex() thrown if a subscript
is beyond the limits of an array. The problem occurs when
the stack-slot for the VAR variable referred to earlier
is occupied by the NUM local variable of finalize_ssa_vuses()
and is overwritten when this variable is assigned a value in
this function.

Comments?

Thanks,
Ranjit.

- --
Ranjit Mathew       Email: rmathew AT gmail DOT com

Bangalore, INDIA.     Web: http://ranjitmathew.hostingzero.com/




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