The spec for llvm.experimental.convergence.entry says that is must be in
the entry block for a function, and must preceed any other convergent
operation. It does not have to be the first instruction in the entry
block.
Inlining assumes that the call to llvm.experimental.convergence.entry
will be the first instruction after any phi instructions. This commit
modifies inlining to search the entire block for the call.
When a convergencectrl token is passed to a convergent call, and the called
function in turn calls the entry intrinsic, the intrinsic is now now replaced
with the convergencectrl token.
The spec requires the following check:
A call from function F to function G can be inlined only if:
- at least one of F or G does not make any convergent calls, or,
- both F and G make the same kind of convergent calls: controlled or
uncontrolled.
But this change does not implement this complete check. A proper implemenation
require a whole new analysis that identifies convergence in every function. For
now, we skip that and just do a cursory check for the entry intrinsic. The
underlying assumption is that in a compiler flow that fully implements
convergence control tokens, there is no mixing of controlled and uncontrolled
convergent operations in the whole program.
This is a reboot of the original change D85606 by
Nicolai Haehnle <nicolai.haehnle@amd.com>.
Reviewed By: arsenm, nhaehnle
Differential Revision: https://reviews.llvm.org/D152431
