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, 152 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/ADT/BitmaskEnum.h b/third_party/llvm-project/include/llvm/ADT/BitmaskEnum.h
new file mode 100644
index 000000000..1a18bc721
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/ADT/BitmaskEnum.h
@@ -0,0 +1,152 @@
+//===-- llvm/ADT/BitmaskEnum.h ----------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_BITMASKENUM_H
+#define LLVM_ADT_BITMASKENUM_H
+
+#include <cassert>
+#include <type_traits>
+#include <utility>
+
+#include "llvm/Support/MathExtras.h"
+
+/// LLVM_MARK_AS_BITMASK_ENUM lets you opt in an individual enum type so you can
+/// perform bitwise operations on it without putting static_cast everywhere.
+///
+/// \code
+///   enum MyEnum {
+///     E1 = 1, E2 = 2, E3 = 4, E4 = 8,
+///     LLVM_MARK_AS_BITMASK_ENUM(/* LargestValue = */ E4)
+///   };
+///
+///   void Foo() {
+///     MyEnum A = (E1 | E2) & E3 ^ ~E4; // Look, ma: No static_cast!
+///   }
+/// \endcode
+///
+/// Normally when you do a bitwise operation on an enum value, you get back an
+/// instance of the underlying type (e.g. int).  But using this macro, bitwise
+/// ops on your enum will return you back instances of the enum.  This is
+/// particularly useful for enums which represent a combination of flags.
+///
+/// The parameter to LLVM_MARK_AS_BITMASK_ENUM should be the largest individual
+/// value in your enum.
+///
+/// All of the enum's values must be non-negative.
+#define LLVM_MARK_AS_BITMASK_ENUM(LargestValue)                                \
+  LLVM_BITMASK_LARGEST_ENUMERATOR = LargestValue
+
+/// LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE() pulls the operator overloads used
+/// by LLVM_MARK_AS_BITMASK_ENUM into the current namespace.
+///
+/// Suppose you have an enum foo::bar::MyEnum.  Before using
+/// LLVM_MARK_AS_BITMASK_ENUM on MyEnum, you must put
+/// LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE() somewhere inside namespace foo or
+/// namespace foo::bar.  This allows the relevant operator overloads to be found
+/// by ADL.
+///
+/// You don't need to use this macro in namespace llvm; it's done at the bottom
+/// of this file.
+#define LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE()                               \
+  using ::llvm::BitmaskEnumDetail::operator~;                                  \
+  using ::llvm::BitmaskEnumDetail::operator|;                                  \
+  using ::llvm::BitmaskEnumDetail::operator&;                                  \
+  using ::llvm::BitmaskEnumDetail::operator^;                                  \
+  using ::llvm::BitmaskEnumDetail::operator|=;                                 \
+  using ::llvm::BitmaskEnumDetail::operator&=;                                 \
+  /* Force a semicolon at the end of this macro. */                            \
+  using ::llvm::BitmaskEnumDetail::operator^=
+
+namespace llvm {
+
+/// Traits class to determine whether an enum has a
+/// LLVM_BITMASK_LARGEST_ENUMERATOR enumerator.
+template <typename E, typename Enable = void>
+struct is_bitmask_enum : std::false_type {};
+
+template <typename E>
+struct is_bitmask_enum<
+    E, typename std::enable_if<sizeof(E::LLVM_BITMASK_LARGEST_ENUMERATOR) >=
+                               0>::type> : std::true_type {};
+namespace BitmaskEnumDetail {
+
+/// Get a bitmask with 1s in all places up to the high-order bit of E's largest
+/// value.
+template <typename E> typename std::underlying_type<E>::type Mask() {
+  // On overflow, NextPowerOf2 returns zero with the type uint64_t, so
+  // subtracting 1 gives us the mask with all bits set, like we want.
+  return NextPowerOf2(static_cast<typename std::underlying_type<E>::type>(
+             E::LLVM_BITMASK_LARGEST_ENUMERATOR)) -
+         1;
+}
+
+/// Check that Val is in range for E, and return Val cast to E's underlying
+/// type.
+template <typename E> typename std::underlying_type<E>::type Underlying(E Val) {
+  auto U = static_cast<typename std::underlying_type<E>::type>(Val);
+  assert(U >= 0 && "Negative enum values are not allowed.");
+  assert(U <= Mask<E>() && "Enum value too large (or largest val too small?)");
+  return U;
+}
+
+template <typename E,
+          typename = typename std::enable_if<is_bitmask_enum<E>::value>::type>
+E operator~(E Val) {
+  return static_cast<E>(~Underlying(Val) & Mask<E>());
+}
+
+template <typename E,
+          typename = typename std::enable_if<is_bitmask_enum<E>::value>::type>
+E operator|(E LHS, E RHS) {
+  return static_cast<E>(Underlying(LHS) | Underlying(RHS));
+}
+
+template <typename E,
+          typename = typename std::enable_if<is_bitmask_enum<E>::value>::type>
+E operator&(E LHS, E RHS) {
+  return static_cast<E>(Underlying(LHS) & Underlying(RHS));
+}
+
+template <typename E,
+          typename = typename std::enable_if<is_bitmask_enum<E>::value>::type>
+E operator^(E LHS, E RHS) {
+  return static_cast<E>(Underlying(LHS) ^ Underlying(RHS));
+}
+
+// |=, &=, and ^= return a reference to LHS, to match the behavior of the
+// operators on builtin types.
+
+template <typename E,
+          typename = typename std::enable_if<is_bitmask_enum<E>::value>::type>
+E &operator|=(E &LHS, E RHS) {
+  LHS = LHS | RHS;
+  return LHS;
+}
+
+template <typename E,
+          typename = typename std::enable_if<is_bitmask_enum<E>::value>::type>
+E &operator&=(E &LHS, E RHS) {
+  LHS = LHS & RHS;
+  return LHS;
+}
+
+template <typename E,
+          typename = typename std::enable_if<is_bitmask_enum<E>::value>::type>
+E &operator^=(E &LHS, E RHS) {
+  LHS = LHS ^ RHS;
+  return LHS;
+}
+
+} // namespace BitmaskEnumDetail
+
+// Enable bitmask enums in namespace ::llvm and all nested namespaces.
+LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE();
+
+} // namespace llvm
+
+#endif