[llvm-commits] [PATCH] ULEB FIXME in ARM back-end

[Renato Golin]

Hi all,

I've been playing with a FIXME in the ARM back-end (to get more
acquainted) and one simple FIXME was an ULEB printing in the
AsmPrinter.

According to the ARM EABI, both build attribute tag and value are
ULEBs and not chars as they were being emitted. Today, I don't know of
any attribute that would emit tags or values bigger than 127 but this
seamed like an easy start.

The patch changes the emission of values to ULEB by storing all tags
and values in a typed list and emit later the right value, computing
the size as it goes. I've run all tests (including the build
attributes ones in ARM be) and it passes everything.

There are three problems I see with this patch, but would like to know
from you what's the best way to solve them:

 1. It uses a local structure to hold both ULEB and String values in
order, but other MC structures will also emit ULEB in the near future
(we should make sure it does, at least), so this structure could
become a proper small class on a more visible place.

 2. It wastes memory since both number and string values are on every
item, but it's not possible to put StringRef in an union since
Stringref has non-trivial constructors. A solution is to use
polymorphism but that's too big for this tiny case. If we decide to
expose the class higher up, then it makes sense to do so.

 3. It's calculating the ULEB size in place, where other routines in
LLVM can do that (but are not accessible from this class). A
refactoring is in need to expose that routine to the intended
audience.

If neither of those problems are relevant, or if they're just minor,
we can put other FIXMEs around. Otherwise, I'm open to suggestions.

best,
--renato
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