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, 103 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/Support/UnicodeCharRanges.h b/third_party/llvm-project/include/llvm/Support/UnicodeCharRanges.h
new file mode 100644
index 000000000..73d3603b7
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/Support/UnicodeCharRanges.h
@@ -0,0 +1,103 @@
+//===--- UnicodeCharRanges.h - Types and functions for character ranges ---===//
+//
+// 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_SUPPORT_UNICODECHARRANGES_H
+#define LLVM_SUPPORT_UNICODECHARRANGES_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+
+#define DEBUG_TYPE "unicode"
+
+namespace llvm {
+namespace sys {
+
+/// Represents a closed range of Unicode code points [Lower, Upper].
+struct UnicodeCharRange {
+  uint32_t Lower;
+  uint32_t Upper;
+};
+
+inline bool operator<(uint32_t Value, UnicodeCharRange Range) {
+  return Value < Range.Lower;
+}
+inline bool operator<(UnicodeCharRange Range, uint32_t Value) {
+  return Range.Upper < Value;
+}
+
+/// Holds a reference to an ordered array of UnicodeCharRange and allows
+/// to quickly check if a code point is contained in the set represented by this
+/// array.
+class UnicodeCharSet {
+public:
+  typedef ArrayRef<UnicodeCharRange> CharRanges;
+
+  /// Constructs a UnicodeCharSet instance from an array of
+  /// UnicodeCharRanges.
+  ///
+  /// Array pointed by \p Ranges should have the lifetime at least as long as
+  /// the UnicodeCharSet instance, and should not change. Array is validated by
+  /// the constructor, so it makes sense to create as few UnicodeCharSet
+  /// instances per each array of ranges, as possible.
+#ifdef NDEBUG
+
+  // FIXME: This could use constexpr + static_assert. This way we
+  // may get rid of NDEBUG in this header. Unfortunately there are some
+  // problems to get this working with MSVC 2013. Change this when
+  // the support for MSVC 2013 is dropped.
+  constexpr UnicodeCharSet(CharRanges Ranges) : Ranges(Ranges) {}
+#else
+  UnicodeCharSet(CharRanges Ranges) : Ranges(Ranges) {
+    assert(rangesAreValid());
+  }
+#endif
+
+  /// Returns true if the character set contains the Unicode code point
+  /// \p C.
+  bool contains(uint32_t C) const {
+    return std::binary_search(Ranges.begin(), Ranges.end(), C);
+  }
+
+private:
+  /// Returns true if each of the ranges is a proper closed range
+  /// [min, max], and if the ranges themselves are ordered and non-overlapping.
+  bool rangesAreValid() const {
+    uint32_t Prev = 0;
+    for (CharRanges::const_iterator I = Ranges.begin(), E = Ranges.end();
+         I != E; ++I) {
+      if (I != Ranges.begin() && Prev >= I->Lower) {
+        LLVM_DEBUG(dbgs() << "Upper bound 0x");
+        LLVM_DEBUG(dbgs().write_hex(Prev));
+        LLVM_DEBUG(dbgs() << " should be less than succeeding lower bound 0x");
+        LLVM_DEBUG(dbgs().write_hex(I->Lower) << "\n");
+        return false;
+      }
+      if (I->Upper < I->Lower) {
+        LLVM_DEBUG(dbgs() << "Upper bound 0x");
+        LLVM_DEBUG(dbgs().write_hex(I->Lower));
+        LLVM_DEBUG(dbgs() << " should not be less than lower bound 0x");
+        LLVM_DEBUG(dbgs().write_hex(I->Upper) << "\n");
+        return false;
+      }
+      Prev = I->Upper;
+    }
+
+    return true;
+  }
+
+  const CharRanges Ranges;
+};
+
+} // namespace sys
+} // namespace llvm
+
+#undef DEBUG_TYPE // "unicode"
+
+#endif // LLVM_SUPPORT_UNICODECHARRANGES_H