On 09/16/14 03:09, Ilya Enkovich wrote:
I must be misunderstanding something then. I fundamentally don't see how
the return bounds are any different here than the return value. If we have
exposed the bounds in the IL, then aren't they going to be handled just like
any other object in the IL?
They are not handled like any other object in IL because return block
and all statements in it are not handled as all other statements we
put into split part.
Here is a comment from find_return_bb:
/* Return basic block containing RETURN statement. We allow basic blocks
of the form:
<retval> = tmp_var;
return <retval>
but return_bb can not be more complex than this.
...
*/
Phi nodes also may present in return_bb.
Right. I've seen this stuff, but it's still not clear to me what the
real issue is.
The first thing that jumps out when I look at your dump is we don't have
a PHI for __bound_tmp.322 in BB6. Now it may be that we really just
wanted __bound_tmp.322_36, but that seems wrong as the return value
varies depending on how we reach BB6 and it seems to me the bounds ought
to vary in a similar manner.
All blocks going to split part are analyzed by visit_bb function.
Return basic block is not analyzed in the same way but still may be
copied into split part in case return value is defined in it. There
is a special code in visit_bb to add args of phi statements of
return_bb as uses of split part to have no undefined values in copied
block. It was enough when those phi args plus return value were only
uses in return_bb.
But now we add returned bounds to GIMPLE_RETURN as a new use and this
new use is ignored. If split part returns value then return_bb will
be copied into it. It means I should check returned bounds are
defined there too. If SSA_NAME_DEF_STMT of returned bounds is in
split part then it is OK. If SSA_NAME_DEF_STMT of returned bounds is
in return_bb then it is also OK because it means it is a result of PHI
node whose args were added as additional uses for split part earlier
in visit_bb.
At least that is how I think this happens :)
Maybe you should post the IL for a case where this all matters and walk me
through the key issues.
I attach a dump I got from Chrome compilation with no additional
checks restrictions in split. Original function returns value defined
by phi node in return_bb and bounds defined in BB2. Split part
contains BB3, BB4 and BB5 and resulting function part has usage of
returned bounds but no producer for it.
Right, but my question is whether or not the bounds from BB2 were really
the correct bounds to be using in the first place! I would have
expected a PHI in BB6 to select the bounds based on the path leading to
BB6, much like we select a different return value.
Jeff
