[LLVMdev] Proposal: extended MDString syntax

[Dan Gohman]

Hello,

I propose a new syntax for metadata strings (MDStrings) which would allow
string data to be spread over multiple lines:

!0 = metadata !{metadata !"""
hello
world
"""}

The special three-quote sequence marks the beginning and end of a
multi-line string.

This syntax could have a variety of uses, but of particular interest is
that it could be used as a basis for serializing MachineFunctions.
MachineFunctions are not an entirely self-contained IR; they contain
references to LLVM IR. As such, a serialization of a MachineFunction needs
to have an LLVM Module to refer to. By encoding MachineFunctions in
metadata, they can easily accompany an LLVM Module. By being multi-line,
the data could be made to be reasonably human-readable and human-editable.

Attached is a simple proof-of-concept patch which implements parsing and
printing for this new MDString syntax.

Comments welcome!

Dan
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