llvm-project

5681859e - [clang] Redefine `noconvergent` and generate convergence control tokens

[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.