[MC/DWARF] Support .debug_frame / .debug_line code alignment factors

[Ulrich Weigand]

Hello,

I've been comparing the object file output of LLVM's integrated
assembler against the external assembler on PowerPC, and one
area where differences still remain are in DWARF sections.

In particular, the GNU assembler generates .debug_frame and
.debug_line sections using a code alignment factor of 4, since
all PowerPC instructions have size 4 and must be aligned to a
multiple of 4.  However, current MC code hard-codes a code
alignment factor of 1.

This patch changes this by adding a "minimum instruction length"
data element to MCAsmInfo and using this as code alignment factor.

This requires passing a MCContext into MCDwarfLineAddr::Encode
and MCDwarfLineAddr::EncodeAdvanceLoc.  Note that one caller,
MCDwarfLineAddr::Write, didn't actually have that information
available.  However, it turns out that this routine is in fact
never used in the whole code base, so the patch simply removes
it.  If it turns out to be needed again at a later time, it
could be re-added with an updated interface.

Does this look OK?

Thanks,
Ulrich
(See attached file: diff-llvm-mc-codealignment)
-------------- next part --------------
A non-text attachment was scrubbed...
Name: diff-llvm-mc-codealignment
Type: application/octet-stream
Size: 10829 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130607/5af1cfb4/attachment.obj>