//! - or-fun-call
//! - option-if-let-else
-use crate::{is_ctor_or_promotable_const_function, is_type_diagnostic_item, match_type, paths};
+use crate::ty::{all_predicates_of, is_copy};
+use crate::visitors::is_const_evaluatable;
use rustc_hir::def::{DefKind, Res};
-
-use rustc_hir::intravisit;
-use rustc_hir::intravisit::{NestedVisitorMap, Visitor};
-
-use rustc_hir::{Block, Expr, ExprKind, Path, QPath};
+use rustc_hir::intravisit::{walk_expr, ErasedMap, NestedVisitorMap, Visitor};
+use rustc_hir::{def_id::DefId, Block, Expr, ExprKind, QPath, UnOp};
use rustc_lint::LateContext;
-use rustc_middle::hir::map::Map;
-use rustc_span::sym;
-
-/// Is the expr pure (is it free from side-effects)?
-/// This function is named so to stress that it isn't exhaustive and returns FNs.
-fn identify_some_pure_patterns(expr: &Expr<'_>) -> bool {
- match expr.kind {
- ExprKind::Lit(..) | ExprKind::ConstBlock(..) | ExprKind::Path(..) | ExprKind::Field(..) => true,
- ExprKind::AddrOf(_, _, addr_of_expr) => identify_some_pure_patterns(addr_of_expr),
- ExprKind::Tup(tup_exprs) => tup_exprs.iter().all(|expr| identify_some_pure_patterns(expr)),
- ExprKind::Struct(_, fields, expr) => {
- fields.iter().all(|f| identify_some_pure_patterns(f.expr))
- && expr.map_or(true, |e| identify_some_pure_patterns(e))
- },
- ExprKind::Call(
- &Expr {
- kind:
- ExprKind::Path(QPath::Resolved(
- _,
- Path {
- res: Res::Def(DefKind::Ctor(..) | DefKind::Variant, ..),
- ..
- },
- )),
- ..
- },
- args,
- ) => args.iter().all(|expr| identify_some_pure_patterns(expr)),
- ExprKind::Block(
- &Block {
- stmts,
- expr: Some(expr),
- ..
- },
- _,
- ) => stmts.is_empty() && identify_some_pure_patterns(expr),
- ExprKind::Box(..)
- | ExprKind::Array(..)
- | ExprKind::Call(..)
- | ExprKind::MethodCall(..)
- | ExprKind::Binary(..)
- | ExprKind::Unary(..)
- | ExprKind::Cast(..)
- | ExprKind::Type(..)
- | ExprKind::DropTemps(..)
- | ExprKind::Loop(..)
- | ExprKind::If(..)
- | ExprKind::Match(..)
- | ExprKind::Closure(..)
- | ExprKind::Block(..)
- | ExprKind::Assign(..)
- | ExprKind::AssignOp(..)
- | ExprKind::Index(..)
- | ExprKind::Break(..)
- | ExprKind::Continue(..)
- | ExprKind::Ret(..)
- | ExprKind::InlineAsm(..)
- | ExprKind::LlvmInlineAsm(..)
- | ExprKind::Repeat(..)
- | ExprKind::Yield(..)
- | ExprKind::Err => false,
+use rustc_middle::ty::{self, PredicateKind};
+use rustc_span::{sym, Symbol};
+use std::cmp;
+use std::ops;
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+enum EagernessSuggestion {
+ // The expression is cheap and should be evaluated eagerly
+ Eager,
+ // The expression may be cheap, so don't suggested lazy evaluation; or the expression may not be safe to switch to
+ // eager evaluation.
+ NoChange,
+ // The expression is likely expensive and should be evaluated lazily.
+ Lazy,
+ // The expression cannot be placed into a closure.
+ ForceNoChange,
+}
+impl ops::BitOr for EagernessSuggestion {
+ type Output = Self;
+ fn bitor(self, rhs: Self) -> Self {
+ cmp::max(self, rhs)
}
}
-
-/// Identify some potentially computationally expensive patterns.
-/// This function is named so to stress that its implementation is non-exhaustive.
-/// It returns FNs and FPs.
-fn identify_some_potentially_expensive_patterns<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
- // Searches an expression for method calls or function calls that aren't ctors
- struct FunCallFinder<'a, 'tcx> {
- cx: &'a LateContext<'tcx>,
- found: bool,
+impl ops::BitOrAssign for EagernessSuggestion {
+ fn bitor_assign(&mut self, rhs: Self) {
+ *self = *self | rhs;
}
+}
- impl<'a, 'tcx> intravisit::Visitor<'tcx> for FunCallFinder<'a, 'tcx> {
- type Map = Map<'tcx>;
-
- fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
- let call_found = match &expr.kind {
- // ignore enum and struct constructors
- ExprKind::Call(..) => !is_ctor_or_promotable_const_function(self.cx, expr),
- ExprKind::Index(obj, _) => {
- let ty = self.cx.typeck_results().expr_ty(obj);
- is_type_diagnostic_item(self.cx, ty, sym::hashmap_type)
- || match_type(self.cx, ty, &paths::BTREEMAP)
- },
- ExprKind::MethodCall(..) => true,
- _ => false,
- };
+/// Determine the eagerness of the given function call.
+fn fn_eagerness(cx: &LateContext<'tcx>, fn_id: DefId, name: Symbol, args: &'tcx [Expr<'_>]) -> EagernessSuggestion {
+ use EagernessSuggestion::{Eager, Lazy, NoChange};
+ let name = &*name.as_str();
- if call_found {
- self.found |= true;
- }
+ let ty = match cx.tcx.impl_of_method(fn_id) {
+ Some(id) => cx.tcx.type_of(id),
+ None => return Lazy,
+ };
- if !self.found {
- intravisit::walk_expr(self, expr);
+ if (name.starts_with("as_") || name == "len" || name == "is_empty") && args.len() == 1 {
+ if matches!(
+ cx.tcx.crate_name(fn_id.krate),
+ sym::std | sym::core | sym::alloc | sym::proc_macro
+ ) {
+ Eager
+ } else {
+ NoChange
+ }
+ } else if let ty::Adt(def, subs) = ty.kind() {
+ // Types where the only fields are generic types (or references to) with no trait bounds other
+ // than marker traits.
+ // Due to the limited operations on these types functions should be fairly cheap.
+ if def
+ .variants
+ .iter()
+ .flat_map(|v| v.fields.iter())
+ .any(|x| matches!(cx.tcx.type_of(x.did).peel_refs().kind(), ty::Param(_)))
+ && all_predicates_of(cx.tcx, fn_id).all(|(pred, _)| match pred.kind().skip_binder() {
+ PredicateKind::Trait(pred) => cx.tcx.trait_def(pred.trait_ref.def_id).is_marker,
+ _ => true,
+ })
+ && subs.types().all(|x| matches!(x.peel_refs().kind(), ty::Param(_)))
+ {
+ // Limit the function to either `(self) -> bool` or `(&self) -> bool`
+ match &**cx.tcx.fn_sig(fn_id).skip_binder().inputs_and_output {
+ [arg, res] if !arg.is_mutable_ptr() && arg.peel_refs() == ty && res.is_bool() => NoChange,
+ _ => Lazy,
}
+ } else {
+ Lazy
}
+ } else {
+ Lazy
+ }
+}
+#[allow(clippy::too_many_lines)]
+fn expr_eagerness(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> EagernessSuggestion {
+ struct V<'cx, 'tcx> {
+ cx: &'cx LateContext<'tcx>,
+ eagerness: EagernessSuggestion,
+ }
+
+ impl<'cx, 'tcx> Visitor<'tcx> for V<'cx, 'tcx> {
+ type Map = ErasedMap<'tcx>;
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
+
+ fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
+ use EagernessSuggestion::{ForceNoChange, Lazy, NoChange};
+ if self.eagerness == ForceNoChange {
+ return;
+ }
+ match e.kind {
+ ExprKind::Call(
+ &Expr {
+ kind: ExprKind::Path(ref path),
+ hir_id,
+ ..
+ },
+ args,
+ ) => match self.cx.qpath_res(path, hir_id) {
+ Res::Def(DefKind::Ctor(..) | DefKind::Variant, _) | Res::SelfCtor(_) => (),
+ Res::Def(_, id) if self.cx.tcx.is_promotable_const_fn(id) => (),
+ // No need to walk the arguments here, `is_const_evaluatable` already did
+ Res::Def(..) if is_const_evaluatable(self.cx, e) => {
+ self.eagerness |= NoChange;
+ return;
+ },
+ Res::Def(_, id) => match path {
+ QPath::Resolved(_, p) => {
+ self.eagerness |= fn_eagerness(self.cx, id, p.segments.last().unwrap().ident.name, args);
+ },
+ QPath::TypeRelative(_, name) => {
+ self.eagerness |= fn_eagerness(self.cx, id, name.ident.name, args);
+ },
+ QPath::LangItem(..) => self.eagerness = Lazy,
+ },
+ _ => self.eagerness = Lazy,
+ },
+ // No need to walk the arguments here, `is_const_evaluatable` already did
+ ExprKind::MethodCall(..) if is_const_evaluatable(self.cx, e) => {
+ self.eagerness |= NoChange;
+ return;
+ },
+ ExprKind::MethodCall(name, _, args, _) => {
+ self.eagerness |= self
+ .cx
+ .typeck_results()
+ .type_dependent_def_id(e.hir_id)
+ .map_or(Lazy, |id| fn_eagerness(self.cx, id, name.ident.name, args));
+ },
+ ExprKind::Index(_, e) => {
+ let ty = self.cx.typeck_results().expr_ty_adjusted(e);
+ if is_copy(self.cx, ty) && !ty.is_ref() {
+ self.eagerness |= NoChange;
+ } else {
+ self.eagerness = Lazy;
+ }
+ },
+
+ // Dereferences should be cheap, but dereferencing a raw pointer earlier may not be safe.
+ ExprKind::Unary(UnOp::Deref, e) if !self.cx.typeck_results().expr_ty(e).is_unsafe_ptr() => (),
+ ExprKind::Unary(UnOp::Deref, _) => self.eagerness |= NoChange,
+
+ ExprKind::Unary(_, e)
+ if matches!(
+ self.cx.typeck_results().expr_ty(e).kind(),
+ ty::Bool | ty::Int(_) | ty::Uint(_),
+ ) => {},
+ ExprKind::Binary(_, lhs, rhs)
+ if self.cx.typeck_results().expr_ty(lhs).is_primitive()
+ && self.cx.typeck_results().expr_ty(rhs).is_primitive() => {},
+
+ // Can't be moved into a closure
+ ExprKind::Break(..)
+ | ExprKind::Continue(_)
+ | ExprKind::Ret(_)
+ | ExprKind::InlineAsm(_)
+ | ExprKind::LlvmInlineAsm(_)
+ | ExprKind::Yield(..)
+ | ExprKind::Err => {
+ self.eagerness = ForceNoChange;
+ return;
+ },
+
+ // Memory allocation, custom operator, loop, or call to an unknown function
+ ExprKind::Box(_)
+ | ExprKind::Unary(..)
+ | ExprKind::Binary(..)
+ | ExprKind::Loop(..)
+ | ExprKind::Call(..) => self.eagerness = Lazy,
+
+ ExprKind::ConstBlock(_)
+ | ExprKind::Array(_)
+ | ExprKind::Tup(_)
+ | ExprKind::Lit(_)
+ | ExprKind::Cast(..)
+ | ExprKind::Type(..)
+ | ExprKind::DropTemps(_)
+ | ExprKind::Let(..)
+ | ExprKind::If(..)
+ | ExprKind::Match(..)
+ | ExprKind::Closure(..)
+ | ExprKind::Field(..)
+ | ExprKind::Path(_)
+ | ExprKind::AddrOf(..)
+ | ExprKind::Struct(..)
+ | ExprKind::Repeat(..)
+ | ExprKind::Block(Block { stmts: [], .. }, _) => (),
+
+ // Assignment might be to a local defined earlier, so don't eagerly evaluate.
+ // Blocks with multiple statements might be expensive, so don't eagerly evaluate.
+ // TODO: Actually check if either of these are true here.
+ ExprKind::Assign(..) | ExprKind::AssignOp(..) | ExprKind::Block(..) => self.eagerness |= NoChange,
+ }
+ walk_expr(self, e);
+ }
}
- let mut finder = FunCallFinder { cx, found: false };
- finder.visit_expr(expr);
- finder.found
+ let mut v = V {
+ cx,
+ eagerness: EagernessSuggestion::Eager,
+ };
+ v.visit_expr(e);
+ v.eagerness
}
-pub fn is_eagerness_candidate<'a, 'tcx>(cx: &'a LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
- !identify_some_potentially_expensive_patterns(cx, expr) && identify_some_pure_patterns(expr)
+/// Whether the given expression should be changed to evaluate eagerly
+pub fn switch_to_eager_eval(cx: &'_ LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
+ expr_eagerness(cx, expr) == EagernessSuggestion::Eager
}
-pub fn is_lazyness_candidate<'a, 'tcx>(cx: &'a LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
- identify_some_potentially_expensive_patterns(cx, expr)
+/// Whether the given expression should be changed to evaluate lazily
+pub fn switch_to_lazy_eval(cx: &'_ LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
+ expr_eagerness(cx, expr) == EagernessSuggestion::Lazy
}
projects / rust.git / blobdiff