InjectExtensions should support multiple patches per file

[PhilippvK]

There is currently no way to have two sets of START/END markers in the same source file (at least not when using the File Name as tag)

It would be great if each set of markers would accept an optional label to differentiate between multiple sections.

[thomasgoodfellow]

The use of the filename as a tag has already proved regrettable when refactoring between LLVM versions led to a filename change. Really these markers should be purely discriptive and located by a search. The current approach was driven largely by the fear that it would be too expensive but having now tried this it showed once again that "premature optimisation is the root of all evil" since the first naive python approach tried scanned 13117125 lines read from 50462 candidate files in just over four seconds on a fairly modest server.

So a proposal for a better approach is to change the YAML index file that drives the inject_extensions script so the file fragment paths have the marker as the key, e.g.:

• name: s4emac
  description: MAC
  patches:
  • Instruction-Layout-TD: s4emac/RISCVInstrInfo_ISAX_S4E_MAC.td
  • Builtins-Table: s4emac/S4E_MAC.builtins.cpp

then the mark "Builtins-Table - INSERTION_START" is found in ./clang/lib/CodeGen/CGBuiltin.cpp, "Instruction-Layout - INSERTION_START" is found in ./llvm/lib/Target/RISCV/RISCVInstrInfo.td, etc. Multiple marks in the same file will be supported, as should applying multiple patch sets, e.g. adding two disjoint extensions.

This would reduce the coupling of the patching script to both the YAML contents and the current LLVM layout. Does it look as if fits your needs?

[thomasgoodfellow]

Adding the trial mark-finder script referred to in previous comment as an aide-memoire
findmarks.txt

[PhilippvK]

The new injection script added in 467b68f#diff-e58a38fb7894b1e0def805c6af3e4cdc1e297e47977a03cae8ac081ec90fb471 suits my needs. However the code needs to be cleaned up (remove commented old code) and missing features should be implemented or dropped (See NotImplementedErrors)