rust/src/consts.rs
2016-02-12 14:30:26 +01:00

558 lines
20 KiB
Rust

#![allow(cast_possible_truncation)]
use rustc::lint::LateContext;
use rustc::middle::const_eval::lookup_const_by_id;
use rustc::middle::def::PathResolution;
use rustc::middle::def::Def;
use rustc_front::hir::*;
use syntax::ptr::P;
use std::cmp::PartialOrd;
use std::cmp::Ordering::{self, Greater, Less, Equal};
use std::rc::Rc;
use std::ops::Deref;
use syntax::ast::Lit_;
use syntax::ast::LitIntType;
use syntax::ast::{UintTy, FloatTy, StrStyle};
use syntax::ast::Sign::{self, Plus, Minus};
#[derive(PartialEq, Eq, Debug, Copy, Clone, Hash)]
pub enum FloatWidth {
Fw32,
Fw64,
FwAny,
}
impl From<FloatTy> for FloatWidth {
fn from(ty: FloatTy) -> FloatWidth {
match ty {
FloatTy::TyF32 => FloatWidth::Fw32,
FloatTy::TyF64 => FloatWidth::Fw64,
}
}
}
/// a Lit_-like enum to fold constant `Expr`s into
#[derive(Eq, Debug, Clone, Hash)]
pub enum Constant {
/// a String "abc"
Str(String, StrStyle),
/// a Binary String b"abc"
Binary(Rc<Vec<u8>>),
/// a single byte b'a'
Byte(u8),
/// a single char 'a'
Char(char),
/// an integer
Int(u64, LitIntType),
/// a float with given type
Float(String, FloatWidth),
/// true or false
Bool(bool),
/// an array of constants
Vec(Vec<Constant>),
/// also an array, but with only one constant, repeated N times
Repeat(Box<Constant>, usize),
/// a tuple of constants
Tuple(Vec<Constant>),
}
impl Constant {
/// convert to u64 if possible
///
/// # panics
///
/// if the constant could not be converted to u64 losslessly
fn as_u64(&self) -> u64 {
if let Constant::Int(val, _) = *self {
val // TODO we may want to check the sign if any
} else {
panic!("Could not convert a {:?} to u64", self);
}
}
/// convert this constant to a f64, if possible
#[allow(cast_precision_loss)]
pub fn as_float(&self) -> Option<f64> {
match *self {
Constant::Byte(b) => Some(b as f64),
Constant::Float(ref s, _) => s.parse().ok(),
Constant::Int(i, ty) => {
Some(if is_negative(ty) {
-(i as f64)
} else {
i as f64
})
}
_ => None,
}
}
}
impl PartialEq for Constant {
fn eq(&self, other: &Constant) -> bool {
match (self, other) {
(&Constant::Str(ref ls, ref lsty), &Constant::Str(ref rs, ref rsty)) => ls == rs && lsty == rsty,
(&Constant::Binary(ref l), &Constant::Binary(ref r)) => l == r,
(&Constant::Byte(l), &Constant::Byte(r)) => l == r,
(&Constant::Char(l), &Constant::Char(r)) => l == r,
(&Constant::Int(lv, lty), &Constant::Int(rv, rty)) => {
lv == rv && (is_negative(lty) & (lv != 0)) == (is_negative(rty) & (rv != 0))
}
(&Constant::Float(ref ls, lw), &Constant::Float(ref rs, rw)) => {
use self::FloatWidth::*;
if match (lw, rw) {
(FwAny, _) | (_, FwAny) | (Fw32, Fw32) | (Fw64, Fw64) => true,
_ => false,
} {
match (ls.parse::<f64>(), rs.parse::<f64>()) {
(Ok(l), Ok(r)) => l.eq(&r),
_ => false,
}
} else {
false
}
}
(&Constant::Bool(l), &Constant::Bool(r)) => l == r,
(&Constant::Vec(ref l), &Constant::Vec(ref r)) => l == r,
(&Constant::Repeat(ref lv, ref ls), &Constant::Repeat(ref rv, ref rs)) => ls == rs && lv == rv,
(&Constant::Tuple(ref l), &Constant::Tuple(ref r)) => l == r,
_ => false, //TODO: Are there inter-type equalities?
}
}
}
impl PartialOrd for Constant {
fn partial_cmp(&self, other: &Constant) -> Option<Ordering> {
match (self, other) {
(&Constant::Str(ref ls, ref lsty), &Constant::Str(ref rs, ref rsty)) => {
if lsty != rsty {
None
} else {
Some(ls.cmp(rs))
}
}
(&Constant::Byte(ref l), &Constant::Byte(ref r)) => Some(l.cmp(r)),
(&Constant::Char(ref l), &Constant::Char(ref r)) => Some(l.cmp(r)),
(&Constant::Int(ref lv, lty), &Constant::Int(ref rv, rty)) => {
Some(match (is_negative(lty) && *lv != 0, is_negative(rty) && *rv != 0) {
(true, true) => rv.cmp(lv),
(false, false) => lv.cmp(rv),
(true, false) => Less,
(false, true) => Greater,
})
}
(&Constant::Float(ref ls, lw), &Constant::Float(ref rs, rw)) => {
use self::FloatWidth::*;
if match (lw, rw) {
(FwAny, _) | (_, FwAny) | (Fw32, Fw32) | (Fw64, Fw64) => true,
_ => false,
} {
match (ls.parse::<f64>(), rs.parse::<f64>()) {
(Ok(ref l), Ok(ref r)) => l.partial_cmp(r),
_ => None,
}
} else {
None
}
}
(&Constant::Bool(ref l), &Constant::Bool(ref r)) => Some(l.cmp(r)),
(&Constant::Vec(ref l), &Constant::Vec(ref r)) => l.partial_cmp(&r),
(&Constant::Repeat(ref lv, ref ls), &Constant::Repeat(ref rv, ref rs)) => {
match lv.partial_cmp(rv) {
Some(Equal) => Some(ls.cmp(rs)),
x => x,
}
}
(&Constant::Tuple(ref l), &Constant::Tuple(ref r)) => l.partial_cmp(r),
_ => None, //TODO: Are there any useful inter-type orderings?
}
}
}
fn lit_to_constant(lit: &Lit_) -> Constant {
match *lit {
Lit_::LitStr(ref is, style) => Constant::Str(is.to_string(), style),
Lit_::LitByte(b) => Constant::Byte(b),
Lit_::LitByteStr(ref s) => Constant::Binary(s.clone()),
Lit_::LitChar(c) => Constant::Char(c),
Lit_::LitInt(value, ty) => Constant::Int(value, ty),
Lit_::LitFloat(ref is, ty) => Constant::Float(is.to_string(), ty.into()),
Lit_::LitFloatUnsuffixed(ref is) => Constant::Float(is.to_string(), FloatWidth::FwAny),
Lit_::LitBool(b) => Constant::Bool(b),
}
}
fn constant_not(o: Constant) -> Option<Constant> {
use syntax::ast::LitIntType::*;
use self::Constant::*;
match o {
Bool(b) => Some(Bool(!b)),
Int(::std::u64::MAX, SignedIntLit(_, Plus)) => None,
Int(value, SignedIntLit(ity, Plus)) => Some(Int(value + 1, SignedIntLit(ity, Minus))),
Int(0, SignedIntLit(ity, Minus)) => Some(Int(1, SignedIntLit(ity, Minus))),
Int(value, SignedIntLit(ity, Minus)) => Some(Int(value - 1, SignedIntLit(ity, Plus))),
Int(value, UnsignedIntLit(ity)) => {
let mask = match ity {
UintTy::TyU8 => ::std::u8::MAX as u64,
UintTy::TyU16 => ::std::u16::MAX as u64,
UintTy::TyU32 => ::std::u32::MAX as u64,
UintTy::TyU64 => ::std::u64::MAX,
UintTy::TyUs => {
return None;
} // refuse to guess
};
Some(Int(!value & mask, UnsignedIntLit(ity)))
},
_ => None,
}
}
fn constant_negate(o: Constant) -> Option<Constant> {
use syntax::ast::LitIntType::*;
use self::Constant::*;
match o {
Int(value, SignedIntLit(ity, sign)) => Some(Int(value, SignedIntLit(ity, neg_sign(sign)))),
Int(value, UnsuffixedIntLit(sign)) => Some(Int(value, UnsuffixedIntLit(neg_sign(sign)))),
Float(is, ty) => Some(Float(neg_float_str(is), ty)),
_ => None,
}
}
fn neg_sign(s: Sign) -> Sign {
match s {
Sign::Plus => Sign::Minus,
Sign::Minus => Sign::Plus,
}
}
fn neg_float_str(s: String) -> String {
if s.starts_with('-') {
s[1..].to_owned()
} else {
format!("-{}", s)
}
}
/// is the given LitIntType negative?
///
/// Examples
///
/// ```
/// assert!(is_negative(UnsuffixedIntLit(Minus)));
/// ```
pub fn is_negative(ty: LitIntType) -> bool {
match ty {
LitIntType::SignedIntLit(_, sign) | LitIntType::UnsuffixedIntLit(sign) => sign == Minus,
LitIntType::UnsignedIntLit(_) => false,
}
}
fn unify_int_type(l: LitIntType, r: LitIntType, s: Sign) -> Option<LitIntType> {
use syntax::ast::LitIntType::*;
match (l, r) {
(SignedIntLit(lty, _), SignedIntLit(rty, _)) => {
if lty == rty {
Some(SignedIntLit(lty, s))
} else {
None
}
}
(UnsignedIntLit(lty), UnsignedIntLit(rty)) => {
if s == Plus && lty == rty {
Some(UnsignedIntLit(lty))
} else {
None
}
}
(UnsuffixedIntLit(_), UnsuffixedIntLit(_)) => Some(UnsuffixedIntLit(s)),
(SignedIntLit(lty, _), UnsuffixedIntLit(_)) => Some(SignedIntLit(lty, s)),
(UnsignedIntLit(lty), UnsuffixedIntLit(rs)) => {
if rs == Plus {
Some(UnsignedIntLit(lty))
} else {
None
}
}
(UnsuffixedIntLit(_), SignedIntLit(rty, _)) => Some(SignedIntLit(rty, s)),
(UnsuffixedIntLit(ls), UnsignedIntLit(rty)) => {
if ls == Plus {
Some(UnsignedIntLit(rty))
} else {
None
}
}
_ => None,
}
}
fn add_neg_int(pos: u64, pty: LitIntType, neg: u64, nty: LitIntType) -> Option<Constant> {
if neg > pos {
unify_int_type(nty, pty, Minus).map(|ty| Constant::Int(neg - pos, ty))
} else {
unify_int_type(nty, pty, Plus).map(|ty| Constant::Int(pos - neg, ty))
}
}
fn sub_int(l: u64, lty: LitIntType, r: u64, rty: LitIntType, neg: bool) -> Option<Constant> {
unify_int_type(lty,
rty,
if neg {
Minus
} else {
Plus
})
.and_then(|ty| l.checked_sub(r).map(|v| Constant::Int(v, ty)))
}
pub fn constant(lcx: &LateContext, e: &Expr) -> Option<(Constant, bool)> {
let mut cx = ConstEvalLateContext {
lcx: Some(lcx),
needed_resolution: false,
};
cx.expr(e).map(|cst| (cst, cx.needed_resolution))
}
pub fn constant_simple(e: &Expr) -> Option<Constant> {
let mut cx = ConstEvalLateContext {
lcx: None,
needed_resolution: false,
};
cx.expr(e)
}
struct ConstEvalLateContext<'c, 'cc: 'c> {
lcx: Option<&'c LateContext<'c, 'cc>>,
needed_resolution: bool,
}
impl<'c, 'cc> ConstEvalLateContext<'c, 'cc> {
/// simple constant folding: Insert an expression, get a constant or none.
fn expr(&mut self, e: &Expr) -> Option<Constant> {
match e.node {
ExprPath(_, _) => self.fetch_path(e),
ExprBlock(ref block) => self.block(block),
ExprIf(ref cond, ref then, ref otherwise) => self.ifthenelse(cond, then, otherwise),
ExprLit(ref lit) => Some(lit_to_constant(&lit.node)),
ExprVec(ref vec) => self.multi(vec).map(Constant::Vec),
ExprTup(ref tup) => self.multi(tup).map(Constant::Tuple),
ExprRepeat(ref value, ref number) => {
self.binop_apply(value, number, |v, n| Some(Constant::Repeat(Box::new(v), n.as_u64() as usize)))
}
ExprUnary(op, ref operand) => {
self.expr(operand).and_then(|o| {
match op {
UnNot => constant_not(o),
UnNeg => constant_negate(o),
UnDeref => Some(o),
}
})
}
ExprBinary(op, ref left, ref right) => self.binop(op, left, right),
// TODO: add other expressions
_ => None,
}
}
/// create `Some(Vec![..])` of all constants, unless there is any
/// non-constant part
fn multi<E: Deref<Target = Expr> + Sized>(&mut self, vec: &[E]) -> Option<Vec<Constant>> {
vec.iter()
.map(|elem| self.expr(elem))
.collect::<Option<_>>()
}
/// lookup a possibly constant expression from a ExprPath
fn fetch_path(&mut self, e: &Expr) -> Option<Constant> {
if let Some(lcx) = self.lcx {
let mut maybe_id = None;
if let Some(&PathResolution { base_def: Def::Const(id), ..}) = lcx.tcx.def_map.borrow().get(&e.id) {
maybe_id = Some(id);
}
// separate if lets to avoid double borrowing the def_map
if let Some(id) = maybe_id {
if let Some(const_expr) = lookup_const_by_id(lcx.tcx, id, None, None) {
let ret = self.expr(const_expr);
if ret.is_some() {
self.needed_resolution = true;
}
return ret;
}
}
}
None
}
/// A block can only yield a constant if it only has one constant expression
fn block(&mut self, block: &Block) -> Option<Constant> {
if block.stmts.is_empty() {
block.expr.as_ref().and_then(|ref b| self.expr(b))
} else {
None
}
}
fn ifthenelse(&mut self, cond: &Expr, then: &Block, otherwise: &Option<P<Expr>>) -> Option<Constant> {
if let Some(Constant::Bool(b)) = self.expr(cond) {
if b {
self.block(then)
} else {
otherwise.as_ref().and_then(|expr| self.expr(expr))
}
} else {
None
}
}
fn binop(&mut self, op: BinOp, left: &Expr, right: &Expr) -> Option<Constant> {
match op.node {
BiAdd => {
self.binop_apply(left, right, |l, r| {
match (l, r) {
(Constant::Byte(l8), Constant::Byte(r8)) => l8.checked_add(r8).map(Constant::Byte),
(Constant::Int(l64, lty), Constant::Int(r64, rty)) => {
let (ln, rn) = (is_negative(lty), is_negative(rty));
if ln == rn {
unify_int_type(lty,
rty,
if ln {
Minus
} else {
Plus
})
.and_then(|ty| l64.checked_add(r64).map(|v| Constant::Int(v, ty)))
} else if ln {
add_neg_int(r64, rty, l64, lty)
} else {
add_neg_int(l64, lty, r64, rty)
}
}
// TODO: float (would need bignum library?)
_ => None,
}
})
}
BiSub => {
self.binop_apply(left, right, |l, r| {
match (l, r) {
(Constant::Byte(l8), Constant::Byte(r8)) => {
if r8 > l8 {
None
} else {
Some(Constant::Byte(l8 - r8))
}
}
(Constant::Int(l64, lty), Constant::Int(r64, rty)) => {
match (is_negative(lty), is_negative(rty)) {
(false, false) => sub_int(l64, lty, r64, rty, r64 > l64),
(true, true) => sub_int(l64, lty, r64, rty, l64 > r64),
(true, false) => {
unify_int_type(lty, rty, Minus)
.and_then(|ty| l64.checked_add(r64).map(|v| Constant::Int(v, ty)))
}
(false, true) => {
unify_int_type(lty, rty, Plus)
.and_then(|ty| l64.checked_add(r64).map(|v| Constant::Int(v, ty)))
}
}
}
_ => None,
}
})
}
BiMul => self.divmul(left, right, u64::checked_mul),
BiDiv => self.divmul(left, right, u64::checked_div),
// BiRem,
BiAnd => self.short_circuit(left, right, false),
BiOr => self.short_circuit(left, right, true),
BiBitXor => self.bitop(left, right, |x, y| x ^ y),
BiBitAnd => self.bitop(left, right, |x, y| x & y),
BiBitOr => self.bitop(left, right, |x, y| (x | y)),
BiShl => self.bitop(left, right, |x, y| x << y),
BiShr => self.bitop(left, right, |x, y| x >> y),
BiEq => self.binop_apply(left, right, |l, r| Some(Constant::Bool(l == r))),
BiNe => self.binop_apply(left, right, |l, r| Some(Constant::Bool(l != r))),
BiLt => self.cmp(left, right, Less, true),
BiLe => self.cmp(left, right, Greater, false),
BiGe => self.cmp(left, right, Less, false),
BiGt => self.cmp(left, right, Greater, true),
_ => None,
}
}
fn divmul<F>(&mut self, left: &Expr, right: &Expr, f: F) -> Option<Constant>
where F: Fn(u64, u64) -> Option<u64>
{
self.binop_apply(left, right, |l, r| {
match (l, r) {
(Constant::Int(l64, lty), Constant::Int(r64, rty)) => {
f(l64, r64).and_then(|value| {
unify_int_type(lty,
rty,
if is_negative(lty) == is_negative(rty) {
Plus
} else {
Minus
})
.map(|ty| Constant::Int(value, ty))
})
}
_ => None,
}
})
}
fn bitop<F>(&mut self, left: &Expr, right: &Expr, f: F) -> Option<Constant>
where F: Fn(u64, u64) -> u64
{
self.binop_apply(left, right, |l, r| {
match (l, r) {
(Constant::Bool(l), Constant::Bool(r)) => Some(Constant::Bool(f(l as u64, r as u64) != 0)),
(Constant::Byte(l8), Constant::Byte(r8)) => Some(Constant::Byte(f(l8 as u64, r8 as u64) as u8)),
(Constant::Int(l, lty), Constant::Int(r, rty)) => {
unify_int_type(lty, rty, Plus).map(|ty| Constant::Int(f(l, r), ty))
}
_ => None,
}
})
}
fn cmp(&mut self, left: &Expr, right: &Expr, ordering: Ordering, b: bool) -> Option<Constant> {
self.binop_apply(left,
right,
|l, r| l.partial_cmp(&r).map(|o| Constant::Bool(b == (o == ordering))))
}
fn binop_apply<F>(&mut self, left: &Expr, right: &Expr, op: F) -> Option<Constant>
where F: Fn(Constant, Constant) -> Option<Constant>
{
if let (Some(lc), Some(rc)) = (self.expr(left), self.expr(right)) {
op(lc, rc)
} else {
None
}
}
fn short_circuit(&mut self, left: &Expr, right: &Expr, b: bool) -> Option<Constant> {
self.expr(left).and_then(|left| {
if let Constant::Bool(lbool) = left {
if lbool == b {
Some(left)
} else {
self.expr(right).and_then(|right| {
if let Constant::Bool(_) = right {
Some(right)
} else {
None
}
})
}
} else {
None
}
})
}
}