Migrate some passes to Mini passes

engine/runtime-compiler/src/main/java/org/enso/compiler/dump/IRDumperPass.java

@@ -3,39 +3,28 @@
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
-import java.util.UUID;
 import org.enso.compiler.context.InlineContext;
 import org.enso.compiler.context.ModuleContext;
 import org.enso.compiler.core.IR;
 import org.enso.compiler.core.ir.Expression;
 import org.enso.compiler.core.ir.Module;
 import org.enso.compiler.pass.IRPass;
+import org.enso.compiler.pass.IRProcessingPass;
 import scala.collection.immutable.Seq;
 
 /** A pass that just dumps IR to the local {@code ir-dumps} directory. See {@link IRDumper}. */
 public class IRDumperPass implements IRPass {
   public static final IRDumperPass INSTANCE = new IRDumperPass();
-  private UUID uuid;
 
   private IRDumperPass() {}
 
   @Override
-  public UUID key() {
-    return uuid;
-  }
-
-  @Override
-  public void org$enso$compiler$pass$IRPass$_setter_$key_$eq(UUID v) {
-    this.uuid = v;
-  }
-
-  @Override
-  public Seq<IRPass> precursorPasses() {
+  public Seq<IRProcessingPass> precursorPasses() {
     return nil();
   }
 
   @Override
-  public Seq<IRPass> invalidatedPasses() {
+  public Seq<IRProcessingPass> invalidatedPasses() {
     return nil();
   }
 
@@ -68,8 +57,8 @@ public <T extends IR> T updateMetadataInDuplicate(T sourceIr, T copyOfIr) {
   }
 
   @SuppressWarnings("unchecked")
-  private static scala.collection.immutable.List<IRPass> nil() {
+  private static scala.collection.immutable.List<IRProcessingPass> nil() {
     Object obj = scala.collection.immutable.Nil$.MODULE$;
-    return (scala.collection.immutable.List<IRPass>) obj;
+    return (scala.collection.immutable.List<IRProcessingPass>) obj;
   }
 }

engine/runtime-compiler/src/main/java/org/enso/compiler/pass/ChainedMiniPass.java

@@ -0,0 +1,51 @@
+package org.enso.compiler.pass;
+
+import java.util.Objects;
+import org.enso.compiler.core.IR;
+import org.enso.compiler.core.ir.Expression;
+
+/** Utility class for chaining mini passes together. */
+final class ChainedMiniPass extends MiniIRPass {
+  private final MiniIRPass firstPass;
+  private final MiniIRPass secondPass;
+
+  private ChainedMiniPass(MiniIRPass firstPass, MiniIRPass secondPass) {
+    this.firstPass = firstPass;
+    this.secondPass = secondPass;
+  }
+
+  static MiniIRPass chain(MiniIRPass firstPass, MiniIRPass secondPass) {
+    if (firstPass == null) {
+      return secondPass;
+    }
+    return new ChainedMiniPass(firstPass, secondPass);
+  }
+
+  @Override
+  public MiniIRPass prepare(IR parent, Expression current) {
+    var first = firstPass.prepare(parent, current);
+    var second = secondPass.prepare(parent, current);
+    if (first == firstPass && second == secondPass) {
+      return this;
+    } else {
+      return new ChainedMiniPass(first, second);
+    }
+  }
+
+  @Override
+  public Expression transformExpression(Expression ir) {
+    var fstIr = firstPass.transformExpression(ir);
+    var sndIr = secondPass.transformExpression(fstIr);
+    return sndIr;
+  }
+
+  @Override
+  public boolean checkPostCondition(IR ir) {
+    return firstPass.checkPostCondition(ir) && secondPass.checkPostCondition(ir);
+  }
+
+  @Override
+  public String toString() {
+    return Objects.toString(firstPass) + ":" + Objects.toString(secondPass);
+  }
+}

engine/runtime-compiler/src/main/java/org/enso/compiler/pass/IRProcessingPass.java

@@ -0,0 +1,16 @@
+package org.enso.compiler.pass;
+
+import org.enso.compiler.core.ir.ProcessingPass;
+import scala.collection.immutable.Seq;
+
+/**
+ * A generic {@link IR} processing pass. Currently with two subclasses: classical {@link IRPass mega
+ * IR processing pass} and {@link MiniPassFactory}.
+ */
+public interface IRProcessingPass extends ProcessingPass {
+  /** The passes that this pass depends _directly_ on to run. */
+  public Seq<? extends IRProcessingPass> precursorPasses();
+
+  /** The passes that are invalidated by running this pass. */
+  public Seq<? extends IRProcessingPass> invalidatedPasses();
+}

engine/runtime-compiler/src/main/java/org/enso/compiler/pass/MiniIRPass.java

@@ -0,0 +1,136 @@
+package org.enso.compiler.pass;
+
+import java.util.function.Function;
+import org.enso.compiler.core.IR;
+import org.enso.compiler.core.ir.Expression;
+import org.enso.compiler.core.ir.Module;
+
+/**
+ * Mini IR pass operates on a single IR element at a time. The {@link org.enso.compiler.Compiler}
+ * traverses the whole IR tree in DFS. It works in two phases.
+ *
+ * <p><b>Note</b> that the current implementation is limited to traverse only {@link
+ * org.enso.compiler.core.ir.Expression} elements as provided by {@link
+ * IR#mapExpressions(Function)}. Hence, the additional method {@link #transformModule(Module)}.
+ *
+ * <p>In the first, <b>prepare</b> phase, the compiler traverses from the root to the leaves and
+ * calls the {@link #prepare(Expression)} method on the mini pass. During this phase, the mini pass
+ * can gather information about the current IR element, but not modify it.
+ *
+ * <p>In the second, <b>transform</b> phase, the compiler returns from the leaves to the root and
+ * calls the {@link #transformExpression(Expression)} method on the mini pass. During this phase,
+ * the mini pass is free to transform the current IR element. The children of the current IR element
+ * are already transformed.
+ *
+ * <p>For each IR element:
+ *
+ * <ol>
+ *   <li>The {@link #prepare(Expression)} method is called to prepare the pass for the current IR
+ *       element. This method is called when the {@link org.enso.compiler.Compiler} traverses the IR
+ *       tree from top to bottom. This is useful for mini passes that need to build some information
+ *       about the current IR element before transforming it. The mini pass must not modify the IR
+ *       element neither attach any metadata to it in this method. By returning {@code null} from
+ *       this method, the mini pass signals to the compiler that it wishes to not process the
+ *       subtree of the current IR element.
+ *   <li>The {@link #transformExpression(Expression)} method is called to transform the current IR
+ *       element. This method is called when the {@link org.enso.compiler.Compiler} traverses the
+ *       element from bottom to top. All the children of the current IR element are already
+ *       transformed when this method is called.
+ * </ol>
+ *
+ * <p>Inspired by: <a href="https://dl.acm.org/doi/10.1145/3140587.3062346">Miniphases: compilation
+ * using modular and efficient tree transformations</a>. PDF available at <a
+ * href="https://infoscience.epfl.ch/server/api/core/bitstreams/8ab72c0a-8aa6-4dee-a704-3504938dc316/content">infoscience.epfl.ch</a>
+ */
+public abstract class MiniIRPass {
+  /**
+   * Prepare the pass for the provided IR element. This method is called when the {@link
+   * org.enso.compiler.Compiler} traverses the IR element from top to bottom.
+   *
+   * <p>The mini pass is free to gather any information about the elements it encounters (via this
+   * method) and use it in the {@link #transformExpression(Expression)} method. Note however, that
+   * it is not wise to store the references to the IR or their children for later comparison in the
+   * {@link #transformExpression(Expression) transform phase}, as the IR tree will most likely be
+   * transformed during the compilation process.
+   *
+   * <p>TL;DR; Do no store references to the IR elements or their children in this method.
+   *
+   * @param parent the the parent of the edge
+   * @param child the child expression element to be be processed.
+   * @return an instance of the pass to process the child's element subtree
+   */
+  public MiniIRPass prepare(IR parent, Expression child) {
+    return this;
+  }
+
+  /**
+   * Transform the provided IR element. Children of the IR element are already transformed when this
+   * method is called. This method is called when the {@link org.enso.compiler.Compiler} traverses
+   * the IR element from bottom to top.
+   *
+   * <p>The pass should not do any traversal in this method.
+   *
+   * @param expr Expression IR element to be transformed by this pass.
+   * @return The transformed Expression IR, or the same IR if no transformation is needed. Must not
+   *     return null.
+   */
+  public abstract Expression transformExpression(Expression expr);
+
+  /**
+   * Transforms the module IR. This is the last method that is called.
+   *
+   * @see #transformExpression(Expression)
+   */
+  public Module transformModule(Module moduleIr) {
+    return moduleIr;
+  }
+
+  public boolean checkPostCondition(IR ir) {
+    return true;
+  }
+
+  /**
+   * Name of the mini pass.
+   *
+   * @return by default it returns name of the implementing class
+   */
+  @Override
+  public String toString() {
+    return getClass().getName();
+  }
+
+  /**
+   * Combines two mini IR passes into one that delegates to both of them.
+   *
+   * @param first first mini pass (can be {@code null})
+   * @param second second mini pass
+   * @return a combined pass that calls both non-{@code null} of the provided passes
+   */
+  public static MiniIRPass combine(MiniIRPass first, MiniIRPass second) {
+    return ChainedMiniPass.chain(first, second);
+  }
+
+  /**
+   * Takes an IR element of given type {@code irType} and transforms it by provided {@link
+   * MiniIRPass}. When assertions are on, the resulting IR is checked with {@link
+   * #checkPostCondition} method of provided {@code miniPass}.
+   *
+   * @param <T> the in and out type of IR
+   * @param irType class of the requested IR type
+   * @param ir the IR element (not {@code null})
+   * @param miniPass the pass to apply
+   * @return the transformed IR
+   */
+  public static <T extends IR> T compile(Class<T> irType, T ir, MiniIRPass miniPass) {
+    var newIr = MiniPassTraverser.compileDeep(ir, miniPass);
+    assert irType.isInstance(newIr)
+        : "Expected "
+            + irType.getName()
+            + " but got "
+            + newIr.getClass().getName()
+            + " by "
+            + miniPass;
+    assert miniPass.checkPostCondition(newIr) : "Post condition failed for " + miniPass;
+    return irType.cast(newIr);
+  }
+}

engine/runtime-compiler/src/main/java/org/enso/compiler/pass/MiniPassFactory.java

@@ -0,0 +1,31 @@
+package org.enso.compiler.pass;
+
+import org.enso.compiler.context.InlineContext;
+import org.enso.compiler.context.ModuleContext;
+
+/**
+ * Mini IR pass operates on a single IR element at a time. The {@link org.enso.compiler.Compiler}
+ * traverses the whole IR tree in DFS. The actual work is done by {@link MiniIRPass} implementation.
+ * This factory only contains a collection of factory methods to create such {@link MiniIRPass IR
+ * mini passes}. If a mini pass supports only inline compilation, its {@link
+ * #createForModuleCompilation(ModuleContext)} method should return null.
+ */
+public interface MiniPassFactory extends IRProcessingPass {
+  /**
+   * Creates an instance of mini pass that is capable of transforming IR elements in the context of
+   * a module.
+   *
+   * @param moduleContext A mini pass can optionally save reference to this module context.
+   * @return May return {@code null} if module compilation is not supported.
+   */
+  MiniIRPass createForModuleCompilation(ModuleContext moduleContext);
+
+  /**
+   * Creates an instance of mini pass that is capable of transforming IR elements in the context of
+   * an inline compilation.
+   *
+   * @param inlineContext A mini pass can optionally save reference to this inline context.
+   * @return Must not return {@code null}. Inline compilation should always be supported.
+   */
+  MiniIRPass createForInlineCompilation(InlineContext inlineContext);
+}

engine/runtime-compiler/src/main/java/org/enso/compiler/pass/MiniPassTraverser.java

@@ -0,0 +1,89 @@
+package org.enso.compiler.pass;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.LinkedList;
+import java.util.List;
+import org.enso.compiler.core.IR;
+import org.enso.compiler.core.ir.Expression;
+import org.enso.compiler.core.ir.Module;
+
+/** Implementation of {@link MiniIRPass#compile}. */
+final class MiniPassTraverser {
+  private final MiniIRPass miniPass;
+  private List<IR> in;
+  private final List<IR> out;
+  private int outIndex;
+
+  private MiniPassTraverser(MiniIRPass miniPass, List<IR> out, int outIndex) {
+    this.miniPass = miniPass;
+    this.out = out;
+    this.outIndex = outIndex;
+  }
+
+  private boolean enqueue(Collection<MiniPassTraverser> queue) {
+    if (in == null) {
+      var ir = out.get(outIndex);
+      in = enqueueSubExpressions(queue, ir, miniPass);
+      return !in.isEmpty();
+    } else {
+      return false;
+    }
+  }
+
+  private void convertExpression() {
+    if (outIndex != -1) {
+      var oldIr = out.get(outIndex);
+      var index = new int[1];
+      var newIr = oldIr.mapExpressions((old) -> (Expression) in.get(index[0]++));
+      var transformedIr =
+          switch (newIr) {
+            case Module m -> miniPass.transformModule(m);
+            case Expression e -> miniPass.transformExpression(e);
+            default -> throw new IllegalArgumentException("" + oldIr);
+          };
+      if (oldIr != transformedIr) {
+        out.set(outIndex, transformedIr);
+      }
+      outIndex = -1;
+    }
+  }
+
+  static IR compileDeep(IR root, MiniIRPass miniPass) {
+    var result = new IR[] {root};
+    var rootTask = new MiniPassTraverser(miniPass, Arrays.asList(result), 0);
+    var stackOfPendingIrs = new LinkedList<MiniPassTraverser>();
+    stackOfPendingIrs.add(rootTask);
+    while (!stackOfPendingIrs.isEmpty()) {
+      if (stackOfPendingIrs.peekLast().enqueue(stackOfPendingIrs)) {
+        // continue descent
+        continue;
+      }
+      var deepestIr = stackOfPendingIrs.removeLast();
+      deepestIr.convertExpression();
+    }
+    assert result[0] != null;
+    return result[0];
+  }
+
+  /**
+   * @param queue queue to put objects in
+   * @param ir IR to process
+   * @param miniPass process with this mini pass
+   * @return {@code true} if the has been modified with new tries to process first
+   */
+  private static List<IR> enqueueSubExpressions(
+      Collection<MiniPassTraverser> queue, IR ir, MiniIRPass miniPass) {
+    var childExpressions = new ArrayList<IR>();
+    var i = new int[1];
+    ir.mapExpressions(
+        (ch) -> {
+          var preparedMiniPass = miniPass.prepare(ir, ch);
+          childExpressions.add(ch);
+          queue.add(new MiniPassTraverser(preparedMiniPass, childExpressions, i[0]++));
+          return ch;
+        });
+    return childExpressions;
+  }
+}