--- /dev/null
+#! /bin/env python3
+
+# Feed this script the output of objdump -M raw --no-show-raw-insn ppc-prog
+
+# It will look for insns that can be represented in compressed mode,
+# according to the encoding rules in the copcond dictionary below.
+
+# Nothing is assumed as to the actual bit-encoding of the insns, this
+# is just to experiment with insn selection and get a quick feedback
+# loop for the encoding options in compressed mode.
+
+# In this script, the computations of encoding modes and transitions
+# are those for attempt 1 encoding, that encompasses:
+
+# - a 16-bit insn (with 10-bit payload) that may switch to compressed
+# mode or return to 32-bit mode;
+
+# - 16-bit insns in compressed mode, each with 2 bits devoted to
+# encoding one of the following possibilities:
+
+# -- switch back to uncompressed mode at the next insn
+
+# -- interpret the next insn in uncompressed mode, then return to
+# compressed mode
+
+# -- remain in 16-bit mode for the next insn
+
+# -- take the 16 bits that would be the next compressed insn as an
+# extension to the present 16-bit insn, and remain in 16-bit mode for
+# the subsequent 16-bits
+
+# At (visible) entry points, mode is forced to return to uncompressed
+# mode.
+
+# The entire code stream is printed, without any attempt to modify the
+# addresses that go along with or in them; we only insert markers for
+# the transition points, and for the compressed instructions.
+
+# The really useful information is printed at the end: a summary of
+# transition and compressed-insn counts, and the achieved compression
+# rate.
+
+import sys
+import re
+
+insn = re.compile('\s+(?P<addr>[0-9a-f]+):\s+(?P<opcode>[^ ]+) *(?P<operands>.*)')
+
+opkind = re.compile('(?P<reg>(?P<regkind>[cf]?r)(?P<regnum>[0-9]+))|(?P<immediate>-?[0-9]+)|(?P<branch>[0-9a-f]+)(?: <.*>)?|(?P<offset>-?[0-9]+)\((?P<basereg>r[0-9]+)\)')
+
+def mapop(op):
+ match = opkind.fullmatch(op)
+
+ if match is None:
+ op = ('other', op)
+ elif match['reg'] is not None:
+ op = (match['regkind'], int(match['regnum']), op)
+ elif match['immediate'] is not None:
+ op = ('imm', int (op).bit_length (), op)
+ elif match['branch'] is not None:
+ op = ('pcoff', (int (match['branch'], 16)
+ - int (addr, 16)).bit_length (), op, addr)
+ elif match['offset'] is not None:
+ op = ('ofst', mapop(match['offset']), mapop(match['basereg']), op)
+ else:
+ raise "unrecognized operand kind"
+
+ return op
+
+def opclass(mop):
+ return mop[0]
+def regno(mop):
+ if mop[0] in { 'r', 'fr', 'cr' }:
+ return mop[1]
+ else:
+ raise "operand is not a register"
+
+def immbits(mop):
+ if mop[0] is 'imm':
+ return mop[1]
+ else:
+ raise "operand is not an immediate"
+
+# Following are predicates to be used in copcond, to tell the mode in
+# which opcode with ops as operands is to be represented
+
+# Any occurrence of the opcode can be compressed.
+def anyops(opcode, ops):
+ return 1
+
+# Compress iff first and second operands are the same.
+def same01(opcode, ops):
+ if ops[0] == ops[1]:
+ return 1
+ else:
+ return 0
+
+# Registers representable in a made-up 3-bit mapping.
+cregs2 = { 1, 2, 3, 4, 5, 6, 7, 31 }
+
+# Return true iff mop is a regular register present in cregs2
+def bin2regs3(mop):
+ return opclass(mop) is 'r' and regno(mop) in cregs2
+
+# Return true iff mop is an immediate of at most 8 bits.
+def imm8(mop):
+ return opclass(mop) is 'imm' and immbits(mop) <= 8
+
+# Compress binary opcodes iff the first two operands (output and first
+# input operand) are registers representable in 3 bits in compressed
+# mode, and the immediate operand can be represented in 8 bits.
+def bin2regs3imm8(opcode, ops):
+ if bin2regs3(ops[0]) and bin2regs3(ops[1]) and imm8(ops[2]):
+ return 1
+ else:
+ return 0
+
+# Map opcodes that might be compressed to a function that returns the
+# best potential encoding kind for the insn, per the numeric coding
+# below.
+copcond = {
+
+}
+
+# We have 4 kinds of insns:
+
+# 0: uncompressed; leave input insn unchanged
+# 1: 16-bit compressed, only in compressed mode
+# 2: 16-bit extended by another 16-bit, only in compressed mode
+# 3: 10-bit compressed, may switch to compressed mode
+
+# count[0:3] count the occurrences of the base kinds.
+# count[4] counts extra 10-bit nop-switches to compressed mode,
+# tentatively introduced before insns that can be 16-bit encoded.
+count = [0,0,0,0,0]
+# Default comments for the insn kinds above. 2 is always tentative.
+comments = ['', '\t; 16-bit', '\t; tentative 16+16-bit', '\t; 10-bit']
+
+# cur stands for the insn kind that we read and processed in the
+# previous iteration of the loop, and prev is the one before it. the
+# one we're processing in the current iteration will be stored in
+# next until we make it cur at the very end of the loop.
+prev = cur = 0
+
+for line in sys.stdin:
+ if line[-1] is '\n':
+ line = line[:-1]
+
+ match = insn.fullmatch(line)
+ if match is None:
+ print(line)
+ # Switch to uncompressed mode at function boundaries
+ prev = prev2 = 0
+ continue
+
+ addr = match['addr']
+ opcode = match['opcode']
+ operands = match['operands']
+
+ if opcode in copcond:
+ next = copcond[opcode](opcode,
+ [mapop(op) for op in operands.split(',')])
+ else:
+ next = 0
+
+ comment = None
+
+ if cur is 0:
+ if next is 0:
+ True # Uncompressed mode for good.
+ elif next is 1:
+ # If cur was not a single uncompressed mode insn,
+ # tentatively encode a 10-bit nop to enter compressed
+ # mode, and then 16-bit. It takes as much space as
+ # encoding as 32-bit, but offers more possibilities for
+ # subsequent compressed encodings. A compressor proper
+ # would have to go back and change the encoding
+ # afterwards, but wé re just counting.
+ if prev is not 1:
+ print('\t\th.nop\t\t; tentatively switch to compressed mode')
+ count[4] += 1
+ comment = 'tentatively compressed to 16-bit'
+ elif next is 2:
+ # We can use compressed encoding for next after an
+ # uncompressed insn only if it's the single-insn
+ # uncompressed mode slot. For anything else, we're better
+ # off using uncompressed encoding for next, since it makes
+ # no sense to spend a 10-bit nop to switch to compressed
+ # mode for a 16+16-bit insn. If subsequent insns would
+ # benefit from compressed encoding, we can switch then.
+ if prev is not 1:
+ next = 0
+ comment = 'not worth a nop for 16+16-bit'
+ elif next is 3:
+ # If prev was 16-bit compressed, cur would be in the
+ # single-insn uncompressed slot, so next could be encoded
+ # as 16-bit, enabling another 1-insn uncompressed slot
+ # after next that a 10-bit insn wouldn't, so make it so.
+ if prev is 1:
+ next = 1
+ comment = '16-bit, could be 10-bit'
+ elif cur is 1:
+ # After a 16-bit insn, anything goes. If it remains in 16-bit
+ # mode, we can have 1 or 2 as next; if it returns to 32-bit
+ # mode, we can have 0 or 3. Using 1 instead of 3 makes room
+ # for a subsequent single-insn compressed mode, so prefer
+ # that.
+ if next is 3:
+ next = 1
+ comment = '16-bit, could be 10-bit'
+ elif cur is 2:
+ # After a 16+16-bit insn, we can't switch directly to 32-bit
+ # mode. However, cur could have been encoded as 32-bit, since
+ # any 16+16-bit insn can. Indeed, we may have an arbitrary
+ # long sequence of 16+16-bit insns before next, and if next
+ # can only be encoded in 32-bit mode, we can "resolve" all
+ # previous adjacent 16+16-bit insns to the corresponding
+ # 32-bit insns in the encoding, and "adjust" the 16-bit or
+ # 10-bit insn that enabled the potential 16+16-bit encoding to
+ # switch to 32-bit mode then instead.
+ if next is 0:
+ prev = cur = 0
+ comment = '32-bit, like tentative 16+16-bit insns above'
+ elif cur is 3:
+ # After a 10-bit insn, another insn that could be encoded as
+ # 10-bit might as well be encoded as 16-bit, to make room for
+ # a single-insn uncompressed insn afterwards.
+ if next is 3:
+ next = 1
+ comment = '16-bit, could be 10-bit'
+ else:
+ raise "unknown mode for previous insn"
+
+ count[next] += 1
+
+ if comment is None:
+ comment = comments[next]
+ else:
+ comment = '\t; ' + comment
+
+ print(line + comment)
+
+ prev = cur
+ cur = next
+
+transition_bytes = 2 * count[4]
+compressed_bytes = 2 * (count[1] + count[3])
+uncompressed_bytes = 4 * (count[0] + count[2])
+total_bytes = transition_bytes + compressed_bytes + uncompressed_bytes
+original_bytes = 2 * compressed_bytes + uncompressed_bytes
+
+print()
+print('Summary')
+print('32-bit uncompressed instructions: %i' % count[0])
+print('16-bit compressed instructions: %i' % count[1])
+print('16+16-bit (tentative) compressed-mode instructions: %i' % count[2])
+print('10-bit compressed instructions: %i' % count[3])
+print('10-bit (tentative) mode-switching nops: %i' % count[4])
+print('Compressed size estimate: %i' % total_bytes)
+print('Original size: %i' % original_bytes)
+print('Compressed/original ratio: %f' % (total_bytes / original_bytes))
projects / libreriscv.git / commitdiff