DWARF parsing and writing support using LLVM (#2520)

This imports LLVM code for DWARF handling. That code has the
Apache 2 license like us. It's also the same code used to
emit DWARF in the common toolchain, so it seems like a safe choice.

This adds two passes: --dwarfdump which runs the same code LLVM
runs for llvm-dwarfdump. This shows we can parse it ok, and will
be useful for debugging. And --dwarfupdate writes out the DWARF
sections (unchanged from what we read, so it just roundtrips - for
updating we need #2515).

This puts LLVM in thirdparty which is added here.

All the LLVM code is behind USE_LLVM_DWARF, which is on
by default, but off in JS for now, as it increases code size by 20%.

This current approach imports the LLVM files directly. This is not
how they are intended to be used, so it required a bunch of
local changes - more than I expected actually, for the platform-specific
stuff. For now this seems to work, so it may be good enough, but
in the long term we may want to switch to linking against libllvm.
A downside to doing that is that binaryen users would need to
have an LLVM build, and even in the waterfall builds we'd have a
problem - while we ship LLVM there anyhow, we constantly update
it, which means that binaryen would need to be on latest llvm all
the time too (which otherwise, given DWARF is quite stable, we
might not need to constantly update).

An even larger issue is that as I did this work I learned about how
DWARF works in LLVM, and while the reading code is easy to
reuse, the writing code is trickier. The main code path is heavily
integrated with the MC layer, which we don't have - we might want
to create a "fake MC layer" for that, but it sounds hard. Instead,
there is the YAML path which is used mostly for testing, and which
can convert DWARF to and from YAML and from binary. Using
the non-YAML parts there, we can convert binary DWARF to
the YAML layer's nice Info data, then convert that to binary. This
works, however, this is not the path LLVM uses normally, and it
supports only some basic DWARF sections - I had to add ranges
support, in fact. So if we need more complex things, we may end
up needing to use the MC layer approach, or consider some other
DWARF library. However, hopefully that should not affect the core
binaryen code which just calls a library for DWARF stuff.

Helps #2400

1 files changed, 278 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/ADT/SmallSet.h b/third_party/llvm-project/include/llvm/ADT/SmallSet.h
new file mode 100644
index 000000000..a03fa7dd8
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/ADT/SmallSet.h
@@ -0,0 +1,278 @@
+//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the SmallSet class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_SMALLSET_H
+#define LLVM_ADT_SMALLSET_H
+
+#include "llvm/ADT/None.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/iterator.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/type_traits.h"
+#include <cstddef>
+#include <functional>
+#include <set>
+#include <type_traits>
+#include <utility>
+
+namespace llvm {
+
+/// SmallSetIterator - This class implements a const_iterator for SmallSet by
+/// delegating to the underlying SmallVector or Set iterators.
+template <typename T, unsigned N, typename C>
+class SmallSetIterator
+    : public iterator_facade_base<SmallSetIterator<T, N, C>,
+                                  std::forward_iterator_tag, T> {
+private:
+  using SetIterTy = typename std::set<T, C>::const_iterator;
+  using VecIterTy = typename SmallVector<T, N>::const_iterator;
+  using SelfTy = SmallSetIterator<T, N, C>;
+
+  /// Iterators to the parts of the SmallSet containing the data. They are set
+  /// depending on isSmall.
+  union {
+    SetIterTy SetIter;
+    VecIterTy VecIter;
+  };
+
+  bool isSmall;
+
+public:
+  SmallSetIterator(SetIterTy SetIter) : SetIter(SetIter), isSmall(false) {}
+
+  SmallSetIterator(VecIterTy VecIter) : VecIter(VecIter), isSmall(true) {}
+
+  // Spell out destructor, copy/move constructor and assignment operators for
+  // MSVC STL, where set<T>::const_iterator is not trivially copy constructible.
+  ~SmallSetIterator() {
+    if (isSmall)
+      VecIter.~VecIterTy();
+    else
+      SetIter.~SetIterTy();
+  }
+
+  SmallSetIterator(const SmallSetIterator &Other) : isSmall(Other.isSmall) {
+    if (isSmall)
+      VecIter = Other.VecIter;
+    else
+      // Use placement new, to make sure SetIter is properly constructed, even
+      // if it is not trivially copy-able (e.g. in MSVC).
+      new (&SetIter) SetIterTy(Other.SetIter);
+  }
+
+  SmallSetIterator(SmallSetIterator &&Other) : isSmall(Other.isSmall) {
+    if (isSmall)
+      VecIter = std::move(Other.VecIter);
+    else
+      // Use placement new, to make sure SetIter is properly constructed, even
+      // if it is not trivially copy-able (e.g. in MSVC).
+      new (&SetIter) SetIterTy(std::move(Other.SetIter));
+  }
+
+  SmallSetIterator& operator=(const SmallSetIterator& Other) {
+    // Call destructor for SetIter, so it gets properly destroyed if it is
+    // not trivially destructible in case we are setting VecIter.
+    if (!isSmall)
+      SetIter.~SetIterTy();
+
+    isSmall = Other.isSmall;
+    if (isSmall)
+      VecIter = Other.VecIter;
+    else
+      new (&SetIter) SetIterTy(Other.SetIter);
+    return *this;
+  }
+
+  SmallSetIterator& operator=(SmallSetIterator&& Other) {
+    // Call destructor for SetIter, so it gets properly destroyed if it is
+    // not trivially destructible in case we are setting VecIter.
+    if (!isSmall)
+      SetIter.~SetIterTy();
+
+    isSmall = Other.isSmall;
+    if (isSmall)
+      VecIter = std::move(Other.VecIter);
+    else
+      new (&SetIter) SetIterTy(std::move(Other.SetIter));
+    return *this;
+  }
+
+  bool operator==(const SmallSetIterator &RHS) const {
+    if (isSmall != RHS.isSmall)
+      return false;
+    if (isSmall)
+      return VecIter == RHS.VecIter;
+    return SetIter == RHS.SetIter;
+  }
+
+  SmallSetIterator &operator++() { // Preincrement
+    if (isSmall)
+      VecIter++;
+    else
+      SetIter++;
+    return *this;
+  }
+
+  const T &operator*() const { return isSmall ? *VecIter : *SetIter; }
+};
+
+/// SmallSet - This maintains a set of unique values, optimizing for the case
+/// when the set is small (less than N).  In this case, the set can be
+/// maintained with no mallocs.  If the set gets large, we expand to using an
+/// std::set to maintain reasonable lookup times.
+template <typename T, unsigned N, typename C = std::less<T>>
+class SmallSet {
+  /// Use a SmallVector to hold the elements here (even though it will never
+  /// reach its 'large' stage) to avoid calling the default ctors of elements
+  /// we will never use.
+  SmallVector<T, N> Vector;
+  std::set<T, C> Set;
+
+  using VIterator = typename SmallVector<T, N>::const_iterator;
+  using mutable_iterator = typename SmallVector<T, N>::iterator;
+
+  // In small mode SmallPtrSet uses linear search for the elements, so it is
+  // not a good idea to choose this value too high. You may consider using a
+  // DenseSet<> instead if you expect many elements in the set.
+  static_assert(N <= 32, "N should be small");
+
+public:
+  using size_type = size_t;
+  using const_iterator = SmallSetIterator<T, N, C>;
+
+  SmallSet() = default;
+
+  LLVM_NODISCARD bool empty() const {
+    return Vector.empty() && Set.empty();
+  }
+
+  size_type size() const {
+    return isSmall() ? Vector.size() : Set.size();
+  }
+
+  /// count - Return 1 if the element is in the set, 0 otherwise.
+  size_type count(const T &V) const {
+    if (isSmall()) {
+      // Since the collection is small, just do a linear search.
+      return vfind(V) == Vector.end() ? 0 : 1;
+    } else {
+      return Set.count(V);
+    }
+  }
+
+  /// insert - Insert an element into the set if it isn't already there.
+  /// Returns true if the element is inserted (it was not in the set before).
+  /// The first value of the returned pair is unused and provided for
+  /// partial compatibility with the standard library self-associative container
+  /// concept.
+  // FIXME: Add iterators that abstract over the small and large form, and then
+  // return those here.
+  std::pair<NoneType, bool> insert(const T &V) {
+    if (!isSmall())
+      return std::make_pair(None, Set.insert(V).second);
+
+    VIterator I = vfind(V);
+    if (I != Vector.end())    // Don't reinsert if it already exists.
+      return std::make_pair(None, false);
+    if (Vector.size() < N) {
+      Vector.push_back(V);
+      return std::make_pair(None, true);
+    }
+
+    // Otherwise, grow from vector to set.
+    while (!Vector.empty()) {
+      Set.insert(Vector.back());
+      Vector.pop_back();
+    }
+    Set.insert(V);
+    return std::make_pair(None, true);
+  }
+
+  template <typename IterT>
+  void insert(IterT I, IterT E) {
+    for (; I != E; ++I)
+      insert(*I);
+  }
+
+  bool erase(const T &V) {
+    if (!isSmall())
+      return Set.erase(V);
+    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
+      if (*I == V) {
+        Vector.erase(I);
+        return true;
+      }
+    return false;
+  }
+
+  void clear() {
+    Vector.clear();
+    Set.clear();
+  }
+
+  const_iterator begin() const {
+    if (isSmall())
+      return {Vector.begin()};
+    return {Set.begin()};
+  }
+
+  const_iterator end() const {
+    if (isSmall())
+      return {Vector.end()};
+    return {Set.end()};
+  }
+
+private:
+  bool isSmall() const { return Set.empty(); }
+
+  VIterator vfind(const T &V) const {
+    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
+      if (*I == V)
+        return I;
+    return Vector.end();
+  }
+};
+
+/// If this set is of pointer values, transparently switch over to using
+/// SmallPtrSet for performance.
+template <typename PointeeType, unsigned N>
+class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
+
+/// Equality comparison for SmallSet.
+///
+/// Iterates over elements of LHS confirming that each element is also a member
+/// of RHS, and that RHS contains no additional values.
+/// Equivalent to N calls to RHS.count.
+/// For small-set mode amortized complexity is O(N^2)
+/// For large-set mode amortized complexity is linear, worst case is O(N^2) (if
+/// every hash collides).
+template <typename T, unsigned LN, unsigned RN, typename C>
+bool operator==(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) {
+  if (LHS.size() != RHS.size())
+    return false;
+
+  // All elements in LHS must also be in RHS
+  return all_of(LHS, [&RHS](const T &E) { return RHS.count(E); });
+}
+
+/// Inequality comparison for SmallSet.
+///
+/// Equivalent to !(LHS == RHS). See operator== for performance notes.
+template <typename T, unsigned LN, unsigned RN, typename C>
+bool operator!=(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) {
+  return !(LHS == RHS);
+}
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_SMALLSET_H