Re: [Jikesrvm-researchers] question about "frameIsRequired" and ECX register in OPT compiler

[David P G. <gr...@us...>]

> I've seen that a method compiled by OPT compiler may not buy a stack
> frame. I was missed in the code to figure out all situations that may or
> may not need a stack frame. I want to use a stack slot if the method has
> any allocation site in it. It seems I do not have to worry about that
> since the allocation site is a GC point, is it correct?

Yes, the allocation sequence contains a call (on the off branch) and thus
will not be a leaf method.  Therefore the opt compiler will buy a
stackframe for the method.

> My second question to confirm the use of the scratch register ECX. Is it
> safe to use it in method prologue and epilogue?
> ( using ECX in
> OPT_StackManager.insertNormalPrologue, and
> OPT_StackManager.insertEpilogue
> )

ECX does not contain a live value on entry or exit from a method, so in
that sense it is fine to use.  The current prologue sequence does use ECX
for a few purposes, but as long as you fit in your new uses around the
already existing ones, it should be fine.

--dave