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, 309 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/ADT/PointerUnion.h b/third_party/llvm-project/include/llvm/ADT/PointerUnion.h
new file mode 100644
index 000000000..98c905775
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/ADT/PointerUnion.h
@@ -0,0 +1,309 @@
+//===- llvm/ADT/PointerUnion.h - Discriminated Union of 2 Ptrs --*- 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 PointerUnion class, which is a discriminated union of
+// pointer types.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_POINTERUNION_H
+#define LLVM_ADT_POINTERUNION_H
+
+#include "llvm/ADT/DenseMapInfo.h"
+#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/Support/PointerLikeTypeTraits.h"
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+
+namespace llvm {
+
+template <typename T> struct PointerUnionTypeSelectorReturn {
+  using Return = T;
+};
+
+/// Get a type based on whether two types are the same or not.
+///
+/// For:
+///
+/// \code
+///   using Ret = typename PointerUnionTypeSelector<T1, T2, EQ, NE>::Return;
+/// \endcode
+///
+/// Ret will be EQ type if T1 is same as T2 or NE type otherwise.
+template <typename T1, typename T2, typename RET_EQ, typename RET_NE>
+struct PointerUnionTypeSelector {
+  using Return = typename PointerUnionTypeSelectorReturn<RET_NE>::Return;
+};
+
+template <typename T, typename RET_EQ, typename RET_NE>
+struct PointerUnionTypeSelector<T, T, RET_EQ, RET_NE> {
+  using Return = typename PointerUnionTypeSelectorReturn<RET_EQ>::Return;
+};
+
+template <typename T1, typename T2, typename RET_EQ, typename RET_NE>
+struct PointerUnionTypeSelectorReturn<
+    PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>> {
+  using Return =
+      typename PointerUnionTypeSelector<T1, T2, RET_EQ, RET_NE>::Return;
+};
+
+namespace pointer_union_detail {
+  /// Determine the number of bits required to store integers with values < n.
+  /// This is ceil(log2(n)).
+  constexpr int bitsRequired(unsigned n) {
+    return n > 1 ? 1 + bitsRequired((n + 1) / 2) : 0;
+  }
+
+  template <typename... Ts> constexpr int lowBitsAvailable() {
+    return std::min<int>({PointerLikeTypeTraits<Ts>::NumLowBitsAvailable...});
+  }
+
+  /// Find the index of a type in a list of types. TypeIndex<T, Us...>::Index
+  /// is the index of T in Us, or sizeof...(Us) if T does not appear in the
+  /// list.
+  template <typename T, typename ...Us> struct TypeIndex;
+  template <typename T, typename ...Us> struct TypeIndex<T, T, Us...> {
+    static constexpr int Index = 0;
+  };
+  template <typename T, typename U, typename... Us>
+  struct TypeIndex<T, U, Us...> {
+    static constexpr int Index = 1 + TypeIndex<T, Us...>::Index;
+  };
+  template <typename T> struct TypeIndex<T> {
+    static constexpr int Index = 0;
+  };
+
+  /// Find the first type in a list of types.
+  template <typename T, typename...> struct GetFirstType {
+    using type = T;
+  };
+
+  /// Provide PointerLikeTypeTraits for void* that is used by PointerUnion
+  /// for the template arguments.
+  template <typename ...PTs> class PointerUnionUIntTraits {
+  public:
+    static inline void *getAsVoidPointer(void *P) { return P; }
+    static inline void *getFromVoidPointer(void *P) { return P; }
+    static constexpr int NumLowBitsAvailable = lowBitsAvailable<PTs...>();
+  };
+
+  /// Implement assigment in terms of construction.
+  template <typename Derived, typename T> struct AssignableFrom {
+    Derived &operator=(T t) {
+      return static_cast<Derived &>(*this) = Derived(t);
+    }
+  };
+
+  template <typename Derived, typename ValTy, int I, typename ...Types>
+  class PointerUnionMembers;
+
+  template <typename Derived, typename ValTy, int I>
+  class PointerUnionMembers<Derived, ValTy, I> {
+  protected:
+    ValTy Val;
+    PointerUnionMembers() = default;
+    PointerUnionMembers(ValTy Val) : Val(Val) {}
+
+    friend struct PointerLikeTypeTraits<Derived>;
+  };
+
+  template <typename Derived, typename ValTy, int I, typename Type,
+            typename ...Types>
+  class PointerUnionMembers<Derived, ValTy, I, Type, Types...>
+      : public PointerUnionMembers<Derived, ValTy, I + 1, Types...> {
+    using Base = PointerUnionMembers<Derived, ValTy, I + 1, Types...>;
+  public:
+    using Base::Base;
+    PointerUnionMembers() = default;
+    PointerUnionMembers(Type V)
+        : Base(ValTy(const_cast<void *>(
+                         PointerLikeTypeTraits<Type>::getAsVoidPointer(V)),
+                     I)) {}
+
+    using Base::operator=;
+    Derived &operator=(Type V) {
+      this->Val = ValTy(
+          const_cast<void *>(PointerLikeTypeTraits<Type>::getAsVoidPointer(V)),
+          I);
+      return static_cast<Derived &>(*this);
+    };
+  };
+}
+
+/// A discriminated union of two or more pointer types, with the discriminator
+/// in the low bit of the pointer.
+///
+/// This implementation is extremely efficient in space due to leveraging the
+/// low bits of the pointer, while exposing a natural and type-safe API.
+///
+/// Common use patterns would be something like this:
+///    PointerUnion<int*, float*> P;
+///    P = (int*)0;
+///    printf("%d %d", P.is<int*>(), P.is<float*>());  // prints "1 0"
+///    X = P.get<int*>();     // ok.
+///    Y = P.get<float*>();   // runtime assertion failure.
+///    Z = P.get<double*>();  // compile time failure.
+///    P = (float*)0;
+///    Y = P.get<float*>();   // ok.
+///    X = P.get<int*>();     // runtime assertion failure.
+template <typename... PTs>
+class PointerUnion
+    : public pointer_union_detail::PointerUnionMembers<
+          PointerUnion<PTs...>,
+          PointerIntPair<
+              void *, pointer_union_detail::bitsRequired(sizeof...(PTs)), int,
+              pointer_union_detail::PointerUnionUIntTraits<PTs...>>,
+          0, PTs...> {
+  // The first type is special because we want to directly cast a pointer to a
+  // default-initialized union to a pointer to the first type. But we don't
+  // want PointerUnion to be a 'template <typename First, typename ...Rest>'
+  // because it's much more convenient to have a name for the whole pack. So
+  // split off the first type here.
+  using First = typename pointer_union_detail::GetFirstType<PTs...>::type;
+  using Base = typename PointerUnion::PointerUnionMembers;
+
+public:
+  PointerUnion() = default;
+
+  PointerUnion(std::nullptr_t) : PointerUnion() {}
+  using Base::Base;
+
+  /// Test if the pointer held in the union is null, regardless of
+  /// which type it is.
+  bool isNull() const { return !this->Val.getPointer(); }
+
+  explicit operator bool() const { return !isNull(); }
+
+  /// Test if the Union currently holds the type matching T.
+  template <typename T> int is() const {
+    constexpr int Index = pointer_union_detail::TypeIndex<T, PTs...>::Index;
+    static_assert(Index < sizeof...(PTs),
+                  "PointerUnion::is<T> given type not in the union");
+    return this->Val.getInt() == Index;
+  }
+
+  /// Returns the value of the specified pointer type.
+  ///
+  /// If the specified pointer type is incorrect, assert.
+  template <typename T> T get() const {
+    assert(is<T>() && "Invalid accessor called");
+    return PointerLikeTypeTraits<T>::getFromVoidPointer(this->Val.getPointer());
+  }
+
+  /// Returns the current pointer if it is of the specified pointer type,
+  /// otherwises returns null.
+  template <typename T> T dyn_cast() const {
+    if (is<T>())
+      return get<T>();
+    return T();
+  }
+
+  /// If the union is set to the first pointer type get an address pointing to
+  /// it.
+  First const *getAddrOfPtr1() const {
+    return const_cast<PointerUnion *>(this)->getAddrOfPtr1();
+  }
+
+  /// If the union is set to the first pointer type get an address pointing to
+  /// it.
+  First *getAddrOfPtr1() {
+    assert(is<First>() && "Val is not the first pointer");
+    assert(
+        PointerLikeTypeTraits<First>::getAsVoidPointer(get<First>()) ==
+            this->Val.getPointer() &&
+        "Can't get the address because PointerLikeTypeTraits changes the ptr");
+    return const_cast<First *>(
+        reinterpret_cast<const First *>(this->Val.getAddrOfPointer()));
+  }
+
+  /// Assignment from nullptr which just clears the union.
+  const PointerUnion &operator=(std::nullptr_t) {
+    this->Val.initWithPointer(nullptr);
+    return *this;
+  }
+
+  /// Assignment from elements of the union.
+  using Base::operator=;
+
+  void *getOpaqueValue() const { return this->Val.getOpaqueValue(); }
+  static inline PointerUnion getFromOpaqueValue(void *VP) {
+    PointerUnion V;
+    V.Val = decltype(V.Val)::getFromOpaqueValue(VP);
+    return V;
+  }
+};
+
+template <typename ...PTs>
+bool operator==(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
+  return lhs.getOpaqueValue() == rhs.getOpaqueValue();
+}
+
+template <typename ...PTs>
+bool operator!=(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
+  return lhs.getOpaqueValue() != rhs.getOpaqueValue();
+}
+
+template <typename ...PTs>
+bool operator<(PointerUnion<PTs...> lhs, PointerUnion<PTs...> rhs) {
+  return lhs.getOpaqueValue() < rhs.getOpaqueValue();
+}
+
+// Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
+// # low bits available = min(PT1bits,PT2bits)-1.
+template <typename ...PTs>
+struct PointerLikeTypeTraits<PointerUnion<PTs...>> {
+  static inline void *getAsVoidPointer(const PointerUnion<PTs...> &P) {
+    return P.getOpaqueValue();
+  }
+
+  static inline PointerUnion<PTs...> getFromVoidPointer(void *P) {
+    return PointerUnion<PTs...>::getFromOpaqueValue(P);
+  }
+
+  // The number of bits available are the min of the pointer types minus the
+  // bits needed for the discriminator.
+  static constexpr int NumLowBitsAvailable = PointerLikeTypeTraits<decltype(
+      PointerUnion<PTs...>::Val)>::NumLowBitsAvailable;
+};
+
+/// A pointer union of three pointer types. See documentation for PointerUnion
+/// for usage.
+template <typename PT1, typename PT2, typename PT3>
+using PointerUnion3 = PointerUnion<PT1, PT2, PT3>;
+
+/// A pointer union of four pointer types. See documentation for PointerUnion
+/// for usage.
+template <typename PT1, typename PT2, typename PT3, typename PT4>
+using PointerUnion4 = PointerUnion<PT1, PT2, PT3, PT4>;
+
+// Teach DenseMap how to use PointerUnions as keys.
+template <typename ...PTs> struct DenseMapInfo<PointerUnion<PTs...>> {
+  using Union = PointerUnion<PTs...>;
+  using FirstInfo =
+      DenseMapInfo<typename pointer_union_detail::GetFirstType<PTs...>::type>;
+
+  static inline Union getEmptyKey() { return Union(FirstInfo::getEmptyKey()); }
+
+  static inline Union getTombstoneKey() {
+    return Union(FirstInfo::getTombstoneKey());
+  }
+
+  static unsigned getHashValue(const Union &UnionVal) {
+    intptr_t key = (intptr_t)UnionVal.getOpaqueValue();
+    return DenseMapInfo<intptr_t>::getHashValue(key);
+  }
+
+  static bool isEqual(const Union &LHS, const Union &RHS) {
+    return LHS == RHS;
+  }
+};
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_POINTERUNION_H