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, 243 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/ADT/PointerIntPair.h b/third_party/llvm-project/include/llvm/ADT/PointerIntPair.h
new file mode 100644
index 000000000..fa6bf1504
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/ADT/PointerIntPair.h
@@ -0,0 +1,243 @@
+//===- llvm/ADT/PointerIntPair.h - Pair for pointer and int -----*- 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 PointerIntPair class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_POINTERINTPAIR_H
+#define LLVM_ADT_POINTERINTPAIR_H
+
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/PointerLikeTypeTraits.h"
+#include "llvm/Support/type_traits.h"
+#include <cassert>
+#include <cstdint>
+#include <limits>
+
+namespace llvm {
+
+template <typename T> struct DenseMapInfo;
+template <typename PointerT, unsigned IntBits, typename PtrTraits>
+struct PointerIntPairInfo;
+
+/// PointerIntPair - This class implements a pair of a pointer and small
+/// integer.  It is designed to represent this in the space required by one
+/// pointer by bitmangling the integer into the low part of the pointer.  This
+/// can only be done for small integers: typically up to 3 bits, but it depends
+/// on the number of bits available according to PointerLikeTypeTraits for the
+/// type.
+///
+/// Note that PointerIntPair always puts the IntVal part in the highest bits
+/// possible.  For example, PointerIntPair<void*, 1, bool> will put the bit for
+/// the bool into bit #2, not bit #0, which allows the low two bits to be used
+/// for something else.  For example, this allows:
+///   PointerIntPair<PointerIntPair<void*, 1, bool>, 1, bool>
+/// ... and the two bools will land in different bits.
+template <typename PointerTy, unsigned IntBits, typename IntType = unsigned,
+          typename PtrTraits = PointerLikeTypeTraits<PointerTy>,
+          typename Info = PointerIntPairInfo<PointerTy, IntBits, PtrTraits>>
+class PointerIntPair {
+  // Used by MSVC visualizer and generally helpful for debugging/visualizing.
+  using InfoTy = Info;
+  intptr_t Value = 0;
+
+public:
+  constexpr PointerIntPair() = default;
+
+  PointerIntPair(PointerTy PtrVal, IntType IntVal) {
+    setPointerAndInt(PtrVal, IntVal);
+  }
+
+  explicit PointerIntPair(PointerTy PtrVal) { initWithPointer(PtrVal); }
+
+  PointerTy getPointer() const { return Info::getPointer(Value); }
+
+  IntType getInt() const { return (IntType)Info::getInt(Value); }
+
+  void setPointer(PointerTy PtrVal) LLVM_LVALUE_FUNCTION {
+    Value = Info::updatePointer(Value, PtrVal);
+  }
+
+  void setInt(IntType IntVal) LLVM_LVALUE_FUNCTION {
+    Value = Info::updateInt(Value, static_cast<intptr_t>(IntVal));
+  }
+
+  void initWithPointer(PointerTy PtrVal) LLVM_LVALUE_FUNCTION {
+    Value = Info::updatePointer(0, PtrVal);
+  }
+
+  void setPointerAndInt(PointerTy PtrVal, IntType IntVal) LLVM_LVALUE_FUNCTION {
+    Value = Info::updateInt(Info::updatePointer(0, PtrVal),
+                            static_cast<intptr_t>(IntVal));
+  }
+
+  PointerTy const *getAddrOfPointer() const {
+    return const_cast<PointerIntPair *>(this)->getAddrOfPointer();
+  }
+
+  PointerTy *getAddrOfPointer() {
+    assert(Value == reinterpret_cast<intptr_t>(getPointer()) &&
+           "Can only return the address if IntBits is cleared and "
+           "PtrTraits doesn't change the pointer");
+    return reinterpret_cast<PointerTy *>(&Value);
+  }
+
+  void *getOpaqueValue() const { return reinterpret_cast<void *>(Value); }
+
+  void setFromOpaqueValue(void *Val) LLVM_LVALUE_FUNCTION {
+    Value = reinterpret_cast<intptr_t>(Val);
+  }
+
+  static PointerIntPair getFromOpaqueValue(void *V) {
+    PointerIntPair P;
+    P.setFromOpaqueValue(V);
+    return P;
+  }
+
+  // Allow PointerIntPairs to be created from const void * if and only if the
+  // pointer type could be created from a const void *.
+  static PointerIntPair getFromOpaqueValue(const void *V) {
+    (void)PtrTraits::getFromVoidPointer(V);
+    return getFromOpaqueValue(const_cast<void *>(V));
+  }
+
+  bool operator==(const PointerIntPair &RHS) const {
+    return Value == RHS.Value;
+  }
+
+  bool operator!=(const PointerIntPair &RHS) const {
+    return Value != RHS.Value;
+  }
+
+  bool operator<(const PointerIntPair &RHS) const { return Value < RHS.Value; }
+  bool operator>(const PointerIntPair &RHS) const { return Value > RHS.Value; }
+
+  bool operator<=(const PointerIntPair &RHS) const {
+    return Value <= RHS.Value;
+  }
+
+  bool operator>=(const PointerIntPair &RHS) const {
+    return Value >= RHS.Value;
+  }
+};
+
+// Specialize is_trivially_copyable to avoid limitation of llvm::is_trivially_copyable
+// when compiled with gcc 4.9.
+template <typename PointerTy, unsigned IntBits, typename IntType,
+          typename PtrTraits,
+          typename Info>
+struct is_trivially_copyable<PointerIntPair<PointerTy, IntBits, IntType, PtrTraits, Info>> : std::true_type {
+#ifdef HAVE_STD_IS_TRIVIALLY_COPYABLE
+  static_assert(std::is_trivially_copyable<PointerIntPair<PointerTy, IntBits, IntType, PtrTraits, Info>>::value,
+                "inconsistent behavior between llvm:: and std:: implementation of is_trivially_copyable");
+#endif
+};
+
+
+template <typename PointerT, unsigned IntBits, typename PtrTraits>
+struct PointerIntPairInfo {
+  static_assert(PtrTraits::NumLowBitsAvailable <
+                    std::numeric_limits<uintptr_t>::digits,
+                "cannot use a pointer type that has all bits free");
+  static_assert(IntBits <= PtrTraits::NumLowBitsAvailable,
+                "PointerIntPair with integer size too large for pointer");
+  enum : uintptr_t {
+    /// PointerBitMask - The bits that come from the pointer.
+    PointerBitMask =
+        ~(uintptr_t)(((intptr_t)1 << PtrTraits::NumLowBitsAvailable) - 1),
+
+    /// IntShift - The number of low bits that we reserve for other uses, and
+    /// keep zero.
+    IntShift = (uintptr_t)PtrTraits::NumLowBitsAvailable - IntBits,
+
+    /// IntMask - This is the unshifted mask for valid bits of the int type.
+    IntMask = (uintptr_t)(((intptr_t)1 << IntBits) - 1),
+
+    // ShiftedIntMask - This is the bits for the integer shifted in place.
+    ShiftedIntMask = (uintptr_t)(IntMask << IntShift)
+  };
+
+  static PointerT getPointer(intptr_t Value) {
+    return PtrTraits::getFromVoidPointer(
+        reinterpret_cast<void *>(Value & PointerBitMask));
+  }
+
+  static intptr_t getInt(intptr_t Value) {
+    return (Value >> IntShift) & IntMask;
+  }
+
+  static intptr_t updatePointer(intptr_t OrigValue, PointerT Ptr) {
+    intptr_t PtrWord =
+        reinterpret_cast<intptr_t>(PtrTraits::getAsVoidPointer(Ptr));
+    assert((PtrWord & ~PointerBitMask) == 0 &&
+           "Pointer is not sufficiently aligned");
+    // Preserve all low bits, just update the pointer.
+    return PtrWord | (OrigValue & ~PointerBitMask);
+  }
+
+  static intptr_t updateInt(intptr_t OrigValue, intptr_t Int) {
+    intptr_t IntWord = static_cast<intptr_t>(Int);
+    assert((IntWord & ~IntMask) == 0 && "Integer too large for field");
+
+    // Preserve all bits other than the ones we are updating.
+    return (OrigValue & ~ShiftedIntMask) | IntWord << IntShift;
+  }
+};
+
+// Provide specialization of DenseMapInfo for PointerIntPair.
+template <typename PointerTy, unsigned IntBits, typename IntType>
+struct DenseMapInfo<PointerIntPair<PointerTy, IntBits, IntType>> {
+  using Ty = PointerIntPair<PointerTy, IntBits, IntType>;
+
+  static Ty getEmptyKey() {
+    uintptr_t Val = static_cast<uintptr_t>(-1);
+    Val <<= PointerLikeTypeTraits<Ty>::NumLowBitsAvailable;
+    return Ty::getFromOpaqueValue(reinterpret_cast<void *>(Val));
+  }
+
+  static Ty getTombstoneKey() {
+    uintptr_t Val = static_cast<uintptr_t>(-2);
+    Val <<= PointerLikeTypeTraits<PointerTy>::NumLowBitsAvailable;
+    return Ty::getFromOpaqueValue(reinterpret_cast<void *>(Val));
+  }
+
+  static unsigned getHashValue(Ty V) {
+    uintptr_t IV = reinterpret_cast<uintptr_t>(V.getOpaqueValue());
+    return unsigned(IV) ^ unsigned(IV >> 9);
+  }
+
+  static bool isEqual(const Ty &LHS, const Ty &RHS) { return LHS == RHS; }
+};
+
+// Teach SmallPtrSet that PointerIntPair is "basically a pointer".
+template <typename PointerTy, unsigned IntBits, typename IntType,
+          typename PtrTraits>
+struct PointerLikeTypeTraits<
+    PointerIntPair<PointerTy, IntBits, IntType, PtrTraits>> {
+  static inline void *
+  getAsVoidPointer(const PointerIntPair<PointerTy, IntBits, IntType> &P) {
+    return P.getOpaqueValue();
+  }
+
+  static inline PointerIntPair<PointerTy, IntBits, IntType>
+  getFromVoidPointer(void *P) {
+    return PointerIntPair<PointerTy, IntBits, IntType>::getFromOpaqueValue(P);
+  }
+
+  static inline PointerIntPair<PointerTy, IntBits, IntType>
+  getFromVoidPointer(const void *P) {
+    return PointerIntPair<PointerTy, IntBits, IntType>::getFromOpaqueValue(P);
+  }
+
+  enum { NumLowBitsAvailable = PtrTraits::NumLowBitsAvailable - IntBits };
+};
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_POINTERINTPAIR_H