[Libre-soc-isa] [Bug 532] discuss iterative approach for statistical analysis of effectiveness of Compressed PowerISA encoding

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=532

--- Comment #7 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
so, logical deduction time.  question: how do we reasonably demonstrate an
approximate compression ratio given that:

a) the C instructions are a common subset
b) the accessible registers likewise.

answer: without near-total-rewrite of gcc llvm binutils, some simple one-line
no-state pattern-matching will suffice:

  foreach insn(objdump):
    if not recognised opcode
       continue
    if not regs recognised by replacement
       continue

this is made slightly more complex by it needing to recognise function name
boundaries (to preserve glibc6 ABI semantics), as well as recognise the entry
and exit from 10bit, 16bit and v3.0B 32bit modes.

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