cranelift-isle: Specialize for Term at rule root (#5295)

In #5174 we decided it doesn't make sense for a rule to have a
bind-pattern at the root of its left-hand side. There's no Rust value
corresponding to the root value of such a term, because it actually
represents a function declaration with one or more arguments.

This commit takes that to its logical conclusion.

`sema::Rule` previously had an `lhs` field whose value must always be a
`Pattern::Term` variant, and anyone using that structure had to deal
with the possibility of finding the wrong variant there.

Now the relevant fields from that variant are stored directly in `Rule`
instead. Also, the (tiny!) portion of `translate_pattern` which applied
when the pattern was the root term is now inlined in `collect_rules`.

Because `translate_pattern` no longer has to special-case the root term,
we can delete its `rule_term` and `is_root` arguments. That brings it
down to a more manageable four arguments, which means many calls fit on
one line now.

cranelift/isle/isle/src/ast.rs

@@ -152,7 +152,6 @@ pub enum Pattern {
 impl Pattern {
     pub fn root_term(&self) -> Option<&Ident> {
         match self {
-            &Pattern::BindPattern { ref subpat, .. } => subpat.root_term(),
             &Pattern::Term { ref sym, .. } => Some(sym),
             _ => None,
         }

cranelift/isle/isle/src/sema.rs

@@ -436,7 +436,9 @@ pub struct Rule {
     /// This rule's id.
     pub id: RuleId,
     /// The left-hand side pattern that this rule matches.
-    pub lhs: Pattern,
+    pub root_term: TermId,
+    /// Patterns to test against the root term's arguments.
+    pub args: Vec<Pattern>,
     /// Any subpattern "if-let" clauses.
     pub iflets: Vec<IfLet>,
     /// The right-hand side expression that this rule evaluates upon successful
@@ -578,15 +580,6 @@ impl Pattern {
         }
     }
 
-    /// Get the root term of this pattern, if any.
-    pub fn root_term(&self) -> Option<TermId> {
-        match self {
-            &Pattern::Term(_, term, _) => Some(term),
-            &Pattern::BindPattern(_, _, ref subpat) => subpat.root_term(),
-            _ => None,
-        }
-    }
-
     /// Recursively visit every sub-pattern.
     pub fn visit<V: PatternVisitor>(
         &self,
@@ -858,15 +851,11 @@ impl Rule {
         let mut vars = HashMap::new();
 
         // Visit the pattern, starting from the root input value.
-        if let &Pattern::Term(_, term, ref args) = &self.lhs {
+        let termdata = &termenv.terms[self.root_term.index()];
-            let termdata = &termenv.terms[term.index()];
+        for (i, (subpat, &arg_ty)) in self.args.iter().zip(termdata.arg_tys.iter()).enumerate() {
-            for (i, (subpat, &arg_ty)) in args.iter().zip(termdata.arg_tys.iter()).enumerate() {
             let value = visitor.add_arg(i, arg_ty);
             visitor.add_pattern(|visitor| subpat.visit(visitor, value, termenv, &mut vars));
         }
-        } else {
-            unreachable!("Pattern must have a term at the root");
-        }
 
         // Visit the `if-let` clauses, using `V::ExprVisitor` for the sub-exprs (right-hand sides).
         for iflet in self.iflets.iter() {
@@ -1648,28 +1637,30 @@ impl TermEnv {
                     let pos = rule.pos;
                     let mut bindings = Bindings::default();
 
-                    let rule_term = match rule.pattern.root_term() {
+                    let (sym, args) = if let ast::Pattern::Term { sym, args, .. } = &rule.pattern {
-                        Some(name) => match self.get_term_by_name(tyenv, name) {
+                        (sym, args)
-                            Some(term) => term,
+                    } else {
-                            None => {
-                                tyenv.report_error(
-                                    pos,
-                                    "Cannot define a rule for an unknown term".to_string(),
-                                );
-                                continue;
-                            }
-                        },
-                        None => {
                         tyenv.report_error(
                             pos,
                             "Rule does not have a term at the root of its left-hand side"
                                 .to_string(),
                         );
                         continue;
-                        }
                     };
 
-                    let pure = match &self.terms[rule_term.index()].kind {
+                    let root_term = if let Some(term) = self.get_term_by_name(tyenv, sym) {
+                        term
+                    } else {
+                        tyenv.report_error(
+                            pos,
+                            "Cannot define a rule for an unknown term".to_string(),
+                        );
+                        continue;
+                    };
+
+                    let termdata = &self.terms[root_term.index()];
+
+                    let pure = match &termdata.kind {
                         &TermKind::Decl { pure, .. } => pure,
                         _ => {
                             tyenv.report_error(
@@ -1681,25 +1672,18 @@ impl TermEnv {
                         }
                     };
 
-                    let (lhs, ty) = unwrap_or_continue!(self.translate_pattern(
+                    termdata.check_args_count(args, tyenv, pos, sym);
-                        tyenv,
+                    let args = self.translate_args(args, termdata, tyenv, &mut bindings);
-                        rule_term,
+
-                        &rule.pattern,
-                        None,
-                        &mut bindings,
-                        /* is_root = */ true,
-                    ));
                     let iflets = rule
                         .iflets
                         .iter()
-                        .filter_map(|iflet| {
+                        .filter_map(|iflet| self.translate_iflet(tyenv, iflet, &mut bindings))
-                            self.translate_iflet(tyenv, rule_term, iflet, &mut bindings)
-                        })
                         .collect();
                     let rhs = unwrap_or_continue!(self.translate_expr(
                         tyenv,
                         &rule.expr,
-                        Some(ty),
+                        Some(termdata.ret_ty),
                         &mut bindings,
                         pure,
                     ));
@@ -1707,7 +1691,8 @@ impl TermEnv {
                     let rid = RuleId(self.rules.len());
                     self.rules.push(Rule {
                         id: rid,
-                        lhs,
+                        root_term,
+                        args,
                         iflets,
                         rhs,
                         vars: bindings.seen,
@@ -1798,11 +1783,9 @@ impl TermEnv {
     fn translate_pattern(
         &self,
         tyenv: &mut TypeEnv,
-        rule_term: TermId,
         pat: &ast::Pattern,
         expected_ty: Option<TypeId>,
         bindings: &mut Bindings,
-        is_root: bool,
     ) -> Option<(Pattern, TypeId)> {
         log!("translate_pattern: {:?}", pat);
         log!("translate_pattern: bindings = {:?}", bindings);
@@ -1858,11 +1841,9 @@ impl TermEnv {
                 for subpat in subpats {
                     let (subpat, ty) = unwrap_or_continue!(self.translate_pattern(
                         tyenv,
-                        rule_term,
+                        subpat,
-                        &*subpat,
                         expected_ty,
                         bindings,
-                        /* is_root = */ false,
                     ));
                     expected_ty = expected_ty.or(Some(ty));
 
@@ -1885,14 +1866,7 @@ impl TermEnv {
                 pos,
             } => {
                 // Do the subpattern first so we can resolve the type for sure.
-                let (subpat, ty) = self.translate_pattern(
+                let (subpat, ty) = self.translate_pattern(tyenv, subpat, expected_ty, bindings)?;
-                    tyenv,
-                    rule_term,
-                    &*subpat,
-                    expected_ty,
-                    bindings,
-                    /* is_root = */ false,
-                )?;
 
                 let name = tyenv.intern_mut(var);
                 if bindings.lookup(name).is_some() {
@@ -1984,11 +1958,9 @@ impl TermEnv {
                         {
                             return self.translate_pattern(
                                 tyenv,
-                                rule_term,
                                 &expanded_pattern,
                                 Some(expected_ty),
                                 bindings,
-                                /* is_root = */ false,
                             );
                         }
 
@@ -2005,10 +1977,6 @@ impl TermEnv {
                 termdata.check_args_count(args, tyenv, pos, sym);
 
                 match &termdata.kind {
-                    TermKind::Decl {
-                        constructor_kind: Some(ConstructorKind::InternalConstructor),
-                        ..
-                    } if is_root && tid == rule_term => {}
                     TermKind::EnumVariant { .. } => {}
                     TermKind::Decl {
                         extractor_kind: Some(ExtractorKind::ExternalExtractor { .. }),
@@ -2024,14 +1992,7 @@ impl TermEnv {
                         // substitutions.
                         log!("internal extractor macro args = {:?}", args);
                         let pat = template.subst_macro_args(&args)?;
-                        return self.translate_pattern(
+                        return self.translate_pattern(tyenv, &pat, expected_ty, bindings);
-                            tyenv,
-                            rule_term,
-                            &pat,
-                            expected_ty,
-                            bindings,
-                            /* is_root = */ false,
-                        );
                     }
                     TermKind::Decl {
                         extractor_kind: None,
@@ -2048,29 +2009,27 @@ impl TermEnv {
                     }
                 }
 
-                // Resolve subpatterns.
+                let subpats = self.translate_args(args, termdata, tyenv, bindings);
-                let subpats = args
-                    .iter()
-                    .zip(termdata.arg_tys.iter())
-                    .filter_map(|(arg, &arg_ty)| {
-                        self.translate_pattern(
-                            tyenv,
-                            rule_term,
-                            arg,
-                            Some(arg_ty),
-                            bindings,
-                            /* is_root = */ false,
-                        )
-                    })
-                    .map(|(subpat, _)| subpat)
-                    .collect();
-
                 Some((Pattern::Term(ty, tid, subpats), ty))
             }
             &ast::Pattern::MacroArg { .. } => unreachable!(),
         }
     }
 
+    fn translate_args(
+        &self,
+        args: &Vec<ast::Pattern>,
+        termdata: &Term,
+        tyenv: &mut TypeEnv,
+        bindings: &mut Bindings,
+    ) -> Vec<Pattern> {
+        args.iter()
+            .zip(termdata.arg_tys.iter())
+            .filter_map(|(arg, &arg_ty)| self.translate_pattern(tyenv, arg, Some(arg_ty), bindings))
+            .map(|(subpat, _)| subpat)
+            .collect()
+    }
+
     fn maybe_implicit_convert_expr(
         &self,
         tyenv: &mut TypeEnv,
@@ -2321,7 +2280,6 @@ impl TermEnv {
     fn translate_iflet(
         &self,
         tyenv: &mut TypeEnv,
-        rule_term: TermId,
         iflet: &ast::IfLet,
         bindings: &mut Bindings,
     ) -> Option<IfLet> {
@@ -2329,14 +2287,7 @@ impl TermEnv {
         let rhs =
             self.translate_expr(tyenv, &iflet.expr, None, bindings, /* pure = */ true)?;
         let ty = rhs.ty();
-        let (lhs, _lhs_ty) = self.translate_pattern(
+        let (lhs, _lhs_ty) = self.translate_pattern(tyenv, &iflet.pattern, Some(ty), bindings)?;
-            tyenv,
-            rule_term,
-            &iflet.pattern,
-            Some(ty),
-            bindings,
-            /* is_root = */ false,
-        )?;
 
         Some(IfLet { lhs, rhs })
     }

cranelift/isle/isle/src/trie.rs

@@ -290,7 +290,6 @@ impl TermFunctionsBuilder {
         log!("termenv: {:?}", termenv);
         for rule in termenv.rules.iter() {
             let (pattern, expr) = lower_rule(termenv, rule.id);
-            let root_term = rule.lhs.root_term().unwrap();
 
             log!(
                 "build:\n- rule {:?}\n- pattern {:?}\n- expr {:?}",
@@ -306,7 +305,7 @@ impl TermFunctionsBuilder {
                 .chain(std::iter::once(TrieSymbol::EndOfMatch));
 
             self.builders_by_term
-                .entry(root_term)
+                .entry(rule.root_term)
                 .or_insert(TrieNode::Empty)
                 .insert(rule.prio, symbols, expr);
         }

cranelift/isle/isle/src/trie_again.rs

@@ -174,7 +174,7 @@ pub fn build(
     let mut errors = Vec::new();
     let mut term = HashMap::new();
     for rule in termenv.rules.iter() {
-        term.entry(rule.lhs.root_term().unwrap())
+        term.entry(rule.root_term)
             .or_insert_with(RuleSetBuilder::default)
             .add_rule(rule, termenv, tyenv, &mut errors);
     }