Merge pull request #36819 from eeckstein/stacklist

SIL: add a StackList data structure with zero cost operations.

Author: eeckstein

include/swift/SIL/BasicBlockBits.h

@@ -14,8 +14,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef SWIFT_SIL_SILBITFIELD_H
-#define SWIFT_SIL_SILBITFIELD_H
+#ifndef SWIFT_SIL_BASICBLOCKBITS_H
+#define SWIFT_SIL_BASICBLOCKBITS_H
 
 #include "swift/SIL/SILFunction.h"
 #include "llvm/ADT/SmallVector.h"
@@ -173,101 +173,6 @@ class BasicBlockSet {
   void erase(SILBasicBlock *block) { flag.reset(block); }
 };
 
-/// An implementation of `llvm::SetVector<SILBasicBlock *,
-///                                       SmallVector<SILBasicBlock *, N>,
-///                                       BasicBlockSet>`.
-///
-/// Unfortunately it's not possible to use `llvm::SetVector` directly because
-/// the BasicBlockSet constructor needs a `SILFunction` argument.
-///
-/// Note: This class does not provide a `remove` method intentinally, because
-/// it would have a O(n) complexity.
-template <unsigned N> class BasicBlockSetVector {
-  using Vector = llvm::SmallVector<SILBasicBlock *, N>;
-
-  Vector vector;
-  BasicBlockSet set;
-  
-public:
-  using iterator = typename Vector::const_iterator;
-
-  BasicBlockSetVector(SILFunction *function) : set(function) {}
-
-  iterator begin() const { return vector.begin(); }
-  iterator end() const { return vector.end(); }
-
-  unsigned size() const { return vector.size(); }
-  bool empty() const { return vector.empty(); }
-
-  bool contains(SILBasicBlock *block) const { return set.contains(block); }
-
-  /// Returns true if \p block was not contained in the set before inserting.
-  bool insert(SILBasicBlock *block) {
-    if (set.insert(block)) {
-      vector.push_back(block);
-      return true;
-    }
-    return false;
-  }
-};
-
-/// A utility for processing basic blocks in a worklist.
-///
-/// It is basically a combination of a block vector and a block set. It can be
-/// used for typical worklist-processing algorithms.
-template <unsigned N> class BasicBlockWorklist {
-  llvm::SmallVector<SILBasicBlock *, N> worklist;
-  BasicBlockSet visited;
-  
-public:
-  /// Construct an empty worklist.
-  BasicBlockWorklist(SILFunction *function) : visited(function) {}
-
-  /// Initialize the worklist with \p initialBlock.
-  BasicBlockWorklist(SILBasicBlock *initialBlock)
-      : visited(initialBlock->getParent()) {
-    push(initialBlock);
-  }
-
-  /// Pops the last added element from the worklist or returns null, if the
-  /// worklist is empty.
-  SILBasicBlock *pop() {
-    if (worklist.empty())
-      return nullptr;
-    return worklist.pop_back_val();
-  }
-
-  /// Pushes \p block onto the worklist if \p block has never been push before.
-  bool pushIfNotVisited(SILBasicBlock *block) {
-    if (visited.insert(block)) {
-      worklist.push_back(block);
-      return true;
-    }
-    return false;
-  }
-
-  /// Like `pushIfNotVisited`, but requires that \p block has never been on the
-  /// worklist before.
-  void push(SILBasicBlock *block) {
-    assert(!visited.contains(block));
-    visited.insert(block);
-    worklist.push_back(block);
-  }
-
-  /// Like `pop`, but marks the returned block as "unvisited". This means, that
-  /// the block can be pushed onto the worklist again.
-  SILBasicBlock *popAndForget() {
-    if (worklist.empty())
-      return nullptr;
-    SILBasicBlock *block = worklist.pop_back_val();
-    visited.erase(block);
-    return block;
-  }
-
-  /// Returns true if \p block was visited, i.e. has been added to the worklist.
-  bool isVisited(SILBasicBlock *block) const { return visited.contains(block); }
-};
-
 } // namespace swift
 
 #endif

include/swift/SIL/BasicBlockDatastructures.h

@@ -0,0 +1,120 @@
+//===--- BasicBlockDatastructures.h -----------------------------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines efficient data structures for working with BasicBlocks.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_SIL_BASICBLOCKDATASTRUCTURES_H
+#define SWIFT_SIL_BASICBLOCKDATASTRUCTURES_H
+
+#include "swift/SIL/StackList.h"
+#include "swift/SIL/BasicBlockBits.h"
+
+namespace swift {
+
+/// An implementation of `llvm::SetVector<SILBasicBlock *,
+///                                       StackList<SILBasicBlock *>,
+///                                       BasicBlockSet>`.
+///
+/// Unfortunately it's not possible to use `llvm::SetVector` directly because
+/// the BasicBlockSet and StackList constructors needs a `SILFunction` argument.
+///
+/// Note: This class does not provide a `remove` method intentinally, because
+/// it would have a O(n) complexity.
+class BasicBlockSetVector {
+  StackList<SILBasicBlock *> vector;
+  BasicBlockSet set;
+  
+public:
+  using iterator = typename StackList<SILBasicBlock *>::iterator;
+
+  BasicBlockSetVector(SILFunction *function) : vector(function), set(function) {}
+
+  iterator begin() const { return vector.begin(); }
+  iterator end() const { return vector.end(); }
+
+  bool empty() const { return vector.empty(); }
+
+  bool contains(SILBasicBlock *block) const { return set.contains(block); }
+
+  /// Returns true if \p block was not contained in the set before inserting.
+  bool insert(SILBasicBlock *block) {
+    if (set.insert(block)) {
+      vector.push_back(block);
+      return true;
+    }
+    return false;
+  }
+};
+
+/// A utility for processing basic blocks in a worklist.
+///
+/// It is basically a combination of a block vector and a block set. It can be
+/// used for typical worklist-processing algorithms.
+class BasicBlockWorklist {
+  StackList<SILBasicBlock *> worklist;
+  BasicBlockSet visited;
+  
+public:
+  /// Construct an empty worklist.
+  BasicBlockWorklist(SILFunction *function)
+    : worklist(function), visited(function) {}
+
+  /// Initialize the worklist with \p initialBlock.
+  BasicBlockWorklist(SILBasicBlock *initialBlock)
+      : BasicBlockWorklist(initialBlock->getParent()) {
+    push(initialBlock);
+  }
+
+  /// Pops the last added element from the worklist or returns null, if the
+  /// worklist is empty.
+  SILBasicBlock *pop() {
+    if (worklist.empty())
+      return nullptr;
+    return worklist.pop_back_val();
+  }
+
+  /// Pushes \p block onto the worklist if \p block has never been push before.
+  bool pushIfNotVisited(SILBasicBlock *block) {
+    if (visited.insert(block)) {
+      worklist.push_back(block);
+      return true;
+    }
+    return false;
+  }
+
+  /// Like `pushIfNotVisited`, but requires that \p block has never been on the
+  /// worklist before.
+  void push(SILBasicBlock *block) {
+    assert(!visited.contains(block));
+    visited.insert(block);
+    worklist.push_back(block);
+  }
+
+  /// Like `pop`, but marks the returned block as "unvisited". This means, that
+  /// the block can be pushed onto the worklist again.
+  SILBasicBlock *popAndForget() {
+    if (worklist.empty())
+      return nullptr;
+    SILBasicBlock *block = worklist.pop_back_val();
+    visited.erase(block);
+    return block;
+  }
+
+  /// Returns true if \p block was visited, i.e. has been added to the worklist.
+  bool isVisited(SILBasicBlock *block) const { return visited.contains(block); }
+};
+
+} // namespace swift
+
+#endif

include/swift/SIL/SILModule.h

@@ -49,10 +49,52 @@
 #include "llvm/Support/raw_ostream.h"
 #include <functional>
 
+namespace swift {
+
+/// A fixed size slab of memory, which can be allocated and freed by the
+/// SILModule at (basically) zero cost.
+class FixedSizeSlab : public llvm::ilist_node<FixedSizeSlab>,
+                       public SILAllocated<FixedSizeSlab> {
+public:
+  /// The capacity of the payload.
+  static constexpr size_t capacity = 64 * sizeof(uintptr_t);
+
+private:
+  friend class SILModule;
+
+  /// The magic number which is stored in overflowGuard.
+  static constexpr uintptr_t magicNumber = (uintptr_t)0xdeadbeafdeadbeafull;
+
+  /// The payload.
+  char data[capacity];
+  
+  /// Used for a cheap buffer overflow check - in the spirit of libgmalloc.
+  uintptr_t overflowGuard = magicNumber;
+
+public:
+  /// Returns the payload pointing to \p T.
+  template<typename T> T *dataFor() { return (T *)(&data[0]); }
+
+  /// Returns the payload pointing to const \p T
+  template<typename T> const T *dataFor() const { return (const T *)(&data[0]); }
+};
+
+} // end swift namespace
+
 namespace llvm {
 namespace yaml {
 class Output;
 } // end namespace yaml
+
+template <>
+struct ilist_traits<::swift::FixedSizeSlab> :
+public ilist_node_traits<::swift::FixedSizeSlab> {
+public:
+  static void deleteNode(::swift::FixedSizeSlab *V) {
+    llvm_unreachable("cannot delete a slab");
+  }
+};
+
 } // end namespace llvm
 
 namespace swift {
@@ -129,6 +171,7 @@ class SILModule {
   };
 
   using ActionCallback = std::function<void()>;
+  using SlabList = llvm::ilist<FixedSizeSlab>;
 
 private:
   friend KeyPathPattern;
@@ -151,6 +194,12 @@ class SILModule {
   /// Allocator that manages the memory of all the pieces of the SILModule.
   mutable llvm::BumpPtrAllocator BPA;
 
+  /// The list of freed slabs, which can be reused.
+  SlabList freeSlabs;
+  
+  /// For consistency checking.
+  size_t numAllocatedSlabs = 0;
+
   /// The swift Module associated with this SILModule.
   ModuleDecl *TheSwiftModule;
 
@@ -733,6 +782,22 @@ class SILModule {
     return static_cast<T *>(allocate(sizeof(T) * Count, alignof(T)));
   }
 
+  /// Allocates a slab of memory.
+  ///
+  /// This has (almost) zero cost, because for the first time, the allocation is
+  /// done with the BPA.
+  /// Subsequent allocations are reusing the already freed slabs.
+  FixedSizeSlab *allocSlab();
+  
+  /// Frees a slab.
+  ///
+  /// This has (almost) zero cost, because the slab is just put into the
+  /// freeSlabs list.
+  void freeSlab(FixedSizeSlab *slab);
+  
+  /// Frees all slabs of a list.
+  void freeAllSlabs(SlabList &slabs);
+
   template <typename T>
   MutableArrayRef<T> allocateCopy(ArrayRef<T> Array) const {
     MutableArrayRef<T> result(allocate<T>(Array.size()), Array.size());