[PATCH] Pack MCSymbol flags and common alignment

[Pete Cooper]

Hi Rafael

MCSymbol has 32-bits of flags and 32-bits of common alignment.

However, we only need to represent power of 2 alignments, and no subclasses need more than 16 bits of flags.  We also have 20 bits of bitfields remaining unused.

This patch takes those 20-bits and exposes them as SubclassData.

On COFF, we used 16-bits for flags and the remainder are unused.
On ELF, we used 5 bits to store the log2(align) which allows alignments up to 2^31, i.e., any power of 2 which fits in an unsigned.  The remaining 15 are enough for the ELF flags.
On MachO, we need 16-bits for flags, and the remaining 4-bits are enough for 2^15 which MCSymbolMachO::getEncodedFlags() already asserted we didn’t exceed.

This ultimately gets MCSymbol down to 24-bits for the base class.  I don’t think its possible to pack the data in any better at this point.

Cheers,
Pete

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