Flang landing in the monorepo

Great, thanks for the update!

MLIR was merged with a 0-parent commit. I take it flang should do the same?

The only significant difference between the approaches I'm aware of is
that if you check out a pre-llvm-merge MLIR commit, all of the checkout
disappears aside from the MLIR sources.

Since flang was developed separately, this seems reasonable.

MLIR history:

* 0f0d0ed1c78 Import MLIR into the LLVM tree

* 5b4a01d4a63 Adjust some MLIR paths and docs
* aed0d21a62d Create README.md

* 6f635f90929 [DWARF] Check that all fields of a Unit Header are read.

I propose to do the same as MLIR, rather than what I outlined below.
Note that this means the flang sources will still be in a flang/
directory, it's just that llvm/ and other directories will be empty for
flang commits until the point of the LLVM merge, when everything will
behave more normally.

(In the previous approach, those directories would contain LLVM as it
appeared at the time of the merge, which will be a fairly arbitrary
commit. That doesn't seem very useful either.)


- Peter

Since no-one commented, I figure it's best to follow MLIR's lead for
consistency. So the history rewriter has been updated to generate a
0-parent commit and a merge:


This decision can still be revisited until the merge occurs!