[lld-macho] Optimize rebase opcode generation
This commit reduces the size of the emitted rebase sections by
generating the REBASE_OPCODE_DO_REBASE_ADD_ADDR_ULEB and
REBASE_OPCODE_DO_REBASE_ULEB_TIMES_SKIPPING_ULEB opcodes.
With this change, chromium_framework's rebase section is a 40% smaller
197 kilobytes, down from the previous 320 kB. That is 6 kB smaller than
what ld64 produces for the same input.
Performance figures from my M1 Mac mini:
x before
+ after
N Min Max Median Avg Stddev
x 10 4.2269349 4.3300061 4.2689675 4.2690016 0.
031151669
+ 10 4.219331 4.2914009 4.2398136 4.2448277 0.
023817308
No difference proven at 95.0% confidence
Differential Revision: https://reviews.llvm.org/D130180