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Removed the Opcode::NotAnOpcode variant, replaced its uses with Option<Opcode>, and used the NonZero optimization to maintain the small 1-byte size of an optional Opcode.

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This commit is contained in:
Angus Holder
2017-02-22 16:13:48 +00:00
committed by Jakob Stoklund Olesen
parent 3d0240d244
commit a4e4776087
6 changed files with 30 additions and 32 deletions
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23
lib/cretonne/meta/gen_instr.py
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@@ -254,9 +254,13 @@ def gen_opcodes(groups, fmt):
fmt.doc_comment('All instructions from all supported ISAs are present.')
fmt.line('#[derive(Copy, Clone, PartialEq, Eq, Debug)]')
instrs = []
# We explicitly set the discriminant of the first variant to 1, which
# allows us to take advantage of the NonZero optimization, meaning that
# wrapping enums can use the 0 discriminant instead of increasing the size
# if the whole type, and so SIZEOF(Option<Opcode>>) == SIZEOF(Opcode)
is_first_opcode = True
with fmt.indented('pub enum Opcode {', '}'):
fmt.doc_comment('An invalid opcode.')
fmt.line('NotAnOpcode,')
for g in groups:
for i in g.instructions:
instrs.append(i)
@@ -269,7 +273,13 @@ def gen_opcodes(groups, fmt):
'Type inferred from {}.'
.format(i.ins[i.format.typevar_operand]))
# Enum variant itself.
fmt.line(i.camel_name + ',')
if is_first_opcode:
fmt.doc_comment('We explicitly set this to 1 to allow the NonZero optimization,')
fmt.doc_comment('meaning that SIZEOF(Option<Opcode>) == SIZEOF(Opcode)')
fmt.line(i.camel_name + ' = 1,')
is_first_opcode = False
else:
fmt.line(i.camel_name + ',')
fmt.line()
with fmt.indented('impl Opcode {', '}'):
@@ -318,7 +328,6 @@ def gen_opcodes(groups, fmt):
# Generate a private opcode_name function.
with fmt.indented('fn opcode_name(opc: Opcode) -> &\'static str {', '}'):
with fmt.indented('match opc {', '}'):
fmt.line('Opcode::NotAnOpcode => "<not an opcode>",')
for i in instrs:
fmt.format('Opcode::{} => "{}",', i.camel_name, i.name)
fmt.line()
@@ -328,13 +337,13 @@ def gen_opcodes(groups, fmt):
instrs,
lambda i: constant_hash.simple_hash(i.name))
with fmt.indented(
'const OPCODE_HASH_TABLE: [Opcode; {}] = ['
'const OPCODE_HASH_TABLE: [Option<Opcode>; {}] = ['
.format(len(hash_table)), '];'):
for i in hash_table:
if i is None:
fmt.line('Opcode::NotAnOpcode,')
fmt.line('None,')
else:
fmt.format('Opcode::{},', i.camel_name)
fmt.format('Some(Opcode::{}),', i.camel_name)
fmt.line()
return instrs