[flang-commits] [flang] [flang][docs] Mark HighLevelFIR transition plan as historical (PR #196227)

[Eugene Epshteyn via flang-commits]

================
@@ -960,55 +960,44 @@ LLVM.
 These high level optimization passes can be run any number of times in any
 order.
 
-## Transition Plan
-
-The new higher-level steps proposed in this document will require significant
-refactoring of lowering. Codegen should not be impacted since the current FIR
-will remain untouched.
-
-A lot of the code in lowering generating Fortran features (like an intrinsic or
-how to do assignments) is based on the fir::ExtendedValue concept. This
-currently is a collection of mlir::Value that allows describing a Fortran object
-(either a variable or an evaluated expression result). The variable and
-expression concepts described above should allow to keep an interface very
-similar to the fir::ExtendedValue, but having the fir::ExtendedValue wrap a
-single value or mlir::Operation* from which all of the object entity
-information can be inferred.
-
-That way, all the helpers currently generating FIR from fir::ExtendedValue could
-be kept and used with the new variable and expression concepts with as little
-modification as possible.
-
-The proposed plan is to:
-- 1. Introduce the new HLFIR operations.
-- 2. Refactor fir::ExtendedValue so that it can work with the new variable and
-     expression concepts (requires part of 1.).
-- 3. Introduce the new translation passes, using the fir::ExtendedValue helpers
-     (requires 1.).
-- 3.b Introduce the new optimization passes (requires 1.).
-- 4. Introduce the fir.declare and hlfir.finalize usage in lowering (requires 1.
-     and 2. and part of 3.).
-
-The following steps might have to be done in parallel of the current lowering,
-to avoid disturbing the work on performance until the new lowering is complete
-and on par.
-
-- 5. Introduce hlfir.designate and hlfir.associate usage in lowering.
-- 6. Introduce lowering to hlfir.assign (with RHS that is not a hlfir.expr),
-     hlfir.ptr_assign.
-- 7. Introduce lowering to hlfir.expr and related operations.
-- 8. Introduce lowering to hlfir.forall.
-
-At that point, lowering using the high-level FIR should be in place, allowing
-extensive testing.
-- 9. Debugging correctness.
-- 10. Debugging execution performance.
-
-The plan is to do these steps incrementally upstream, but for lowering this will
-most likely be safer to do have the new expression lowering implemented in
-parallel upstream, and to add an option to use the new lowering rather than to
-directly modify the current expression lowering and have it step by step
-equivalent functionally and performance wise.
+## Transition (Historical)
----------------
eugeneepshteyn wrote:

Is it worth rewriting and keeping this section, or should we just remove it?

https://github.com/llvm/llvm-project/pull/196227