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, 110 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/MC/MCRegister.h b/third_party/llvm-project/include/llvm/MC/MCRegister.h
new file mode 100644
index 000000000..8372947a4
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/MC/MCRegister.h
@@ -0,0 +1,110 @@
+//===-- llvm/MC/Register.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_MC_REGISTER_H
+#define LLVM_MC_REGISTER_H
+
+#include "llvm/ADT/DenseMapInfo.h"
+#include <cassert>
+
+namespace llvm {
+
+/// An unsigned integer type large enough to represent all physical registers,
+/// but not necessarily virtual registers.
+using MCPhysReg = uint16_t;
+
+/// Wrapper class representing physical registers. Should be passed by value.
+class MCRegister {
+  unsigned Reg;
+
+public:
+  MCRegister(unsigned Val = 0): Reg(Val) {}
+
+  // Register numbers can represent physical registers, virtual registers, and
+  // sometimes stack slots. The unsigned values are divided into these ranges:
+  //
+  //   0           Not a register, can be used as a sentinel.
+  //   [1;2^30)    Physical registers assigned by TableGen.
+  //   [2^30;2^31) Stack slots. (Rarely used.)
+  //   [2^31;2^32) Virtual registers assigned by MachineRegisterInfo.
+  //
+  // Further sentinels can be allocated from the small negative integers.
+  // DenseMapInfo<unsigned> uses -1u and -2u.
+
+  /// This is the portion of the positive number space that is not a physical
+  /// register. StackSlot values do not exist in the MC layer, see
+  /// Register::isStackSlot() for the more information on them.
+  ///
+  /// Note that isVirtualRegister() and isPhysicalRegister() cannot handle stack
+  /// slots, so if a variable may contains a stack slot, always check
+  /// isStackSlot() first.
+  static bool isStackSlot(unsigned Reg) {
+    return int(Reg) >= (1 << 30);
+  }
+
+  /// Return true if the specified register number is in
+  /// the physical register namespace.
+  static bool isPhysicalRegister(unsigned Reg) {
+    assert(!isStackSlot(Reg) && "Not a register! Check isStackSlot() first.");
+    return int(Reg) > 0;
+  }
+
+  /// Return true if the specified register number is in the physical register
+  /// namespace.
+  bool isPhysical() const {
+    return isPhysicalRegister(Reg);
+  }
+
+  operator unsigned() const {
+    return Reg;
+  }
+
+  unsigned id() const {
+    return Reg;
+  }
+
+  bool isValid() const {
+    return Reg != 0;
+  }
+
+  /// Comparisons between register objects
+  bool operator==(const MCRegister &Other) const { return Reg == Other.Reg; }
+  bool operator!=(const MCRegister &Other) const { return Reg != Other.Reg; }
+
+  /// Comparisons against register constants. E.g.
+  /// * R == AArch64::WZR
+  /// * R == 0
+  /// * R == VirtRegMap::NO_PHYS_REG
+  bool operator==(unsigned Other) const { return Reg == Other; }
+  bool operator!=(unsigned Other) const { return Reg != Other; }
+  bool operator==(int Other) const { return Reg == unsigned(Other); }
+  bool operator!=(int Other) const { return Reg != unsigned(Other); }
+  // MSVC requires that we explicitly declare these two as well.
+  bool operator==(MCPhysReg Other) const { return Reg == unsigned(Other); }
+  bool operator!=(MCPhysReg Other) const { return Reg != unsigned(Other); }
+};
+
+// Provide DenseMapInfo for MCRegister
+template<> struct DenseMapInfo<MCRegister> {
+  static inline unsigned getEmptyKey() {
+    return DenseMapInfo<unsigned>::getEmptyKey();
+  }
+  static inline unsigned getTombstoneKey() {
+    return DenseMapInfo<unsigned>::getTombstoneKey();
+  }
+  static unsigned getHashValue(const MCRegister &Val) {
+    return DenseMapInfo<unsigned>::getHashValue(Val.id());
+  }
+  static bool isEqual(const MCRegister &LHS, const MCRegister &RHS) {
+    return DenseMapInfo<unsigned>::isEqual(LHS.id(), RHS.id());
+  }
+};
+
+}
+
+#endif // ifndef LLVM_MC_REGISTER_H