tree ba0c37590c1ac3026adaf1ef43484d12097892b4
parent 4ddf344b77cc01282571c643d621af34e6a7d8ad
author Sameer Sahasrabuddhe <sameer.sahasrabuddhe@amd.com> 1744720201 +0530
committer Sameer Sahasrabuddhe <sameer.sahasrabuddhe@amd.com> 1744959381 +0530

[clang] Redefine `noconvergent` and generate convergence control tokens

This introduces the `-fconvergence-control` flag that emits convergence control
intrinsics which are then used as the `convergencectrl` operand bundle on
convergent calls.

This also redefines the `noconvergent` attribute in Clang. The existing simple
interpretation is that if a statement is marked `noconvergent`, then every asm
call is treated as a non-convergent operation in the emitted LLVM IR.

The new semantics introduces a more powerful notion that a `noconvergent`
statement may contain convergent operations, but the resulting convergence
constraints are limited to the scope of that statement. As a whole the statement
itself does not place any convergence constraints on the control flow reaching
it. When emitting convergence tokens, this attribute results in a call to the
`anchor` intrinsic that determines convergence within the statement.