On Fri, Sep 13, 2013 at 4:29 PM, Eric Botcazou <ebotca...@adacore.com> wrote:
> Hi,
>
> in Ada parameters can be passed by reference: in this case, the address of the
> argument is directly passed to the callee, which dereferences it to access the
> argument; now Ada also enables -fexceptions -fnon-call-exceptions, which means
> that any pointer dereference is seen as the potential source of an exception,
> which can quickly block the optimizer. That's why we put TREE_THIS_NOTRAP on
> the dereferences associated with a parameter.
>
> This works fine as long as the function isn't inlined, because it may happen
> that the argument is itself the dereference of a pointer, properly guarded by
> a null check on the pointer. When the function is inlined, the dereference in
> the caller is replaced with that of the callee, which is TREE_THIS_NOTRAP and
> thus can be moved ahead of the null pointer check, for example by LIM.
>
> The patch ensures that this cannot happen by clearing TREE_THIS_NOTRAP in the
> inliner. I think that this affects only the Ada compiler in practice.
>
> Tested on x86_64-suse-linux, OK for the mainline?
I've looked at the C++ testcase
int foo (int &x)
{
try {
return x;
}
catch (...)
{
return 0;
}
}
which exhibits exactly the behavior you quote - return x is considered throwing
an exception. The C++ FE doesn't arrange for TREE_THIS_NOTRAP to be
set here (maybe due to this issue you quote?).
Other than that the patch looks reasonable (I suppose you need
is_parameter_of only because as we recursively handle the trees
PARM_DECLs from the destination could already have leaked into
the tree we recurse into?)
Thanks,
Richard.
>
> 2013-09-13 Eric Botcazou <ebotca...@adacore.com>
>
> * tree-inline.h (struct copy_body_data): Add transform_parameter.
> * tree-inline.c (is_parameter_of): New predicate.
> (remap_gimple_op_r): Do not propagate TREE_THIS_NOTRAP on MEM_REF if
> a parameter has been remapped.
> (copy_tree_body_r): Likewise on INDIRECT_REF and MEM_REF.
> (optimize_inline_calls): Initialize transform_parameter.
> (unsave_expr_now): Likewise.
> (copy_gimple_seq_and_replace_locals): Likewise.
> (tree_function_versioning): Likewise.
> (maybe_inline_call_in_expr): Likewise.
>
>
> 2013-09-13 Eric Botcazou <ebotca...@adacore.com>
>
> * gnat.dg/opt27.adb: New test.
> * gnat.dg/opt27_pkg.ad[sb]: New helper.
>
>
> --
> Eric Botcazou
