Hi Jeff,
On 9/19/23 07:59, Jeff Law wrote:
On 9/18/23 21:37, Vineet Gupta wrote:
On 9/18/23 19:41, Jeff Law wrote:
On 9/18/23 13:45, Vineet Gupta wrote:
For the cases which do require sign extends, but not being
eliminated due to "missing definition(s)" I'm working on adapting
Ajit's REE ABI interfaces work [2] to work for RISC-V as well.
I wonder if we could walk the DECL_ARGUMENTS for
current_function_decl and create sign extensions for integer
arguments smaller than XLEN at the start of the function. Record
them in a list.
Then we just let the rest of REE do its thing. When REE is done we
go back and delete those sign extensions we created.
[..]
Right. What I'm suggesting is to create an explicit extension in the
IL at the very beginning of REE for the appropriate arguments. Put
the extension in the entry block.
That would make extensions that were previously in the RTL redundant
allowing REE to remove them.
Then we also remove the explicitly added extensions.
Think of the extensions we're adding as expressing the the extension
that the caller would have done and would expose the redundant
extensions in the callee. We put them in the IL merely to make the
existing REE algorithm happy. Once they've served their purpose in
exposing redundant extensions we remove the ones we added.
If you're familiar with DSE there's a lot of similarities with how we
discover dead stores into the stack. We pretend there's a store to
each local frame slot in the epilogue, that in turn exposes stores
into the local frame that would never be read because we're exiting
the function.
We touched upon this in our airport "rendezvous". I'm curious if you
have the wip bits lying around - (a) to get a feel for how this could be
done and (b) to see why REE and/or similar construct in CSE don't work
as expected.
Thx,
-Vineet
