Hi Philipp,
On 1/9/22 21:56, Philipp Tomsich wrote:
> This adds the possibility to specify a predicate-function that is
> called as part of decoding in multi-patterns; it is intended for
> use-cases (such as vendor-defined instructions in RISC-V) where the
> same bitpattern may decode into different functions depending on the
> overall configuration of the emulation target.
But for a particular CPU, its "vendor ISAs" won't change at runtime.
Since we know this at build time, I don't understand why you need
predicate support at all.
>
> At this time, we only support predicates for multi-patterns.
>
> Signed-off-by: Philipp Tomsich <philipp.toms...@vrull.eu>
>
> ---
>
> docs/devel/decodetree.rst | 7 ++++++-
> scripts/decodetree.py | 24 +++++++++++++++++++++---
> 2 files changed, 27 insertions(+), 4 deletions(-)
>
> diff --git a/docs/devel/decodetree.rst b/docs/devel/decodetree.rst
> index 49ea50c2a7..241aaec8bb 100644
> --- a/docs/devel/decodetree.rst
> +++ b/docs/devel/decodetree.rst
> @@ -144,9 +144,10 @@ Patterns
> Syntax::
>
> pat_def := identifier ( pat_elt )+
> - pat_elt := fixedbit_elt | field_elt | field_ref | args_ref | fmt_ref
> | const_elt
> + pat_elt := fixedbit_elt | field_elt | field_ref | args_ref | fmt_ref
> | const_elt | predicate
> fmt_ref := '@' identifier
> const_elt := identifier '=' number
> + predicate := '|' identifier
>
> The *fixedbit_elt* and *field_elt* specifiers are unchanged from formats.
> A pattern that does not specify a named format will have one inferred
> @@ -156,6 +157,10 @@ A *const_elt* allows a argument to be set to a constant
> value. This may
> come in handy when fields overlap between patterns and one has to
> include the values in the *fixedbit_elt* instead.
>
> +A *predicate* allows to specify a predicate function (returing true or
> +false) to determine the applicability of the pattern. Currently, this
> +will change the decode-behaviour for overlapping multi-patterns only.
> +
> The decoder will call a translator function for each pattern matched.
>
> Pattern examples::
> diff --git a/scripts/decodetree.py b/scripts/decodetree.py
> index a03dc6b5e3..7da2282411 100644
> --- a/scripts/decodetree.py
> +++ b/scripts/decodetree.py
> @@ -52,6 +52,7 @@
> re_fld_ident = '%[a-zA-Z0-9_]*'
> re_fmt_ident = '@[a-zA-Z0-9_]*'
> re_pat_ident = '[a-zA-Z0-9_]*'
> +re_predicate_ident = '\|[a-zA-Z_][a-zA-Z0-9_]*'
>
> def error_with_file(file, lineno, *args):
> """Print an error message from file:line and args and exit."""
> @@ -119,6 +120,14 @@ def whexC(val):
> suffix = 'u'
> return whex(val) + suffix
>
> +def predicate(val):
> + """Return a string for calling a predicate function
> + (if specified, accepting 'None' as an indication
> + that no predicate is to be emitted) with the ctx
> + as a parameter."""
> + if (val == None):
> + return ''
> + return ' && ' + val + '(ctx)'
>
> def str_match_bits(bits, mask):
> """Return a string pretty-printing BITS/MASK"""
> @@ -340,7 +349,7 @@ def output_def(self):
>
> class General:
> """Common code between instruction formats and instruction patterns"""
> - def __init__(self, name, lineno, base, fixb, fixm, udfm, fldm, flds, w):
> + def __init__(self, name, lineno, base, fixb, fixm, udfm, fldm, flds, w,
> p = None):
> self.name = name
> self.file = input_file
> self.lineno = lineno
> @@ -351,6 +360,7 @@ def __init__(self, name, lineno, base, fixb, fixm, udfm,
> fldm, flds, w):
> self.fieldmask = fldm
> self.fields = flds
> self.width = w
> + self.predicate = p
>
> def __str__(self):
> return self.name + ' ' + str_match_bits(self.fixedbits,
> self.fixedmask)
> @@ -499,7 +509,7 @@ def output_code(self, i, extracted, outerbits, outermask):
> if outermask != p.fixedmask:
> innermask = p.fixedmask & ~outermask
> innerbits = p.fixedbits & ~outermask
> - output(ind, f'if ((insn & {whexC(innermask)}) ==
> {whexC(innerbits)}) {{\n')
> + output(ind, f'if ((insn & {whexC(innermask)}) ==
> {whexC(innerbits)}{predicate(p.predicate)}) {{\n')
> output(ind, f' /* {str_match_bits(p.fixedbits,
> p.fixedmask)} */\n')
> p.output_code(i + 4, extracted, p.fixedbits, p.fixedmask)
> output(ind, '}\n')
> @@ -826,6 +836,7 @@ def parse_generic(lineno, parent_pat, name, toks):
> global re_fld_ident
> global re_fmt_ident
> global re_C_ident
> + global re_predicate_ident
> global insnwidth
> global insnmask
> global variablewidth
> @@ -839,6 +850,7 @@ def parse_generic(lineno, parent_pat, name, toks):
> flds = {}
> arg = None
> fmt = None
> + predicate = None
> for t in toks:
> # '&Foo' gives a format an explicit argument set.
> if re.fullmatch(re_arg_ident, t):
> @@ -881,6 +893,12 @@ def parse_generic(lineno, parent_pat, name, toks):
> flds = add_field(lineno, flds, fname, ConstField(value))
> continue
>
> + # '|predicate' sets a predicate function to be called.
> + if re.fullmatch(re_predicate_ident, t):
> + tt = t[1:]
> + predicate = tt;
> + continue
> +
> # Pattern of 0s, 1s, dots and dashes indicate required zeros,
> # required ones, or dont-cares.
> if re.fullmatch('[01.-]+', t):
> @@ -979,7 +997,7 @@ def parse_generic(lineno, parent_pat, name, toks):
> if f not in flds.keys() and f not in fmt.fields.keys():
> error(lineno, f'field {f} not initialized')
> pat = Pattern(name, lineno, fmt, fixedbits, fixedmask,
> - undefmask, fieldmask, flds, width)
> + undefmask, fieldmask, flds, width, predicate)
> parent_pat.pats.append(pat)
> allpatterns.append(pat)
>
