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, 171 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/Support/Chrono.h b/third_party/llvm-project/include/llvm/Support/Chrono.h
new file mode 100644
index 000000000..334ab6083
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/Support/Chrono.h
@@ -0,0 +1,171 @@
+//===- llvm/Support/Chrono.h - Utilities for Timing Manipulation-*- 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_SUPPORT_CHRONO_H
+#define LLVM_SUPPORT_CHRONO_H
+
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/FormatProviders.h"
+
+#include <chrono>
+#include <ctime>
+
+namespace llvm {
+
+class raw_ostream;
+
+namespace sys {
+
+/// A time point on the system clock. This is provided for two reasons:
+/// - to insulate us agains subtle differences in behavoir to differences in
+///   system clock precision (which is implementation-defined and differs between
+///   platforms).
+/// - to shorten the type name
+/// The default precision is nanoseconds. If need a specific precision specify
+/// it explicitly. If unsure, use the default. If you need a time point on a
+/// clock other than the system_clock, use std::chrono directly.
+template <typename D = std::chrono::nanoseconds>
+using TimePoint = std::chrono::time_point<std::chrono::system_clock, D>;
+
+/// Convert a TimePoint to std::time_t
+inline std::time_t toTimeT(TimePoint<> TP) {
+  using namespace std::chrono;
+  return system_clock::to_time_t(
+      time_point_cast<system_clock::time_point::duration>(TP));
+}
+
+/// Convert a std::time_t to a TimePoint
+inline TimePoint<std::chrono::seconds>
+toTimePoint(std::time_t T) {
+  using namespace std::chrono;
+  return time_point_cast<seconds>(system_clock::from_time_t(T));
+}
+
+/// Convert a std::time_t + nanoseconds to a TimePoint
+inline TimePoint<>
+toTimePoint(std::time_t T, uint32_t nsec) {
+  using namespace std::chrono;
+  return time_point_cast<nanoseconds>(system_clock::from_time_t(T))
+    + nanoseconds(nsec);
+}
+
+} // namespace sys
+
+raw_ostream &operator<<(raw_ostream &OS, sys::TimePoint<> TP);
+
+/// Format provider for TimePoint<>
+///
+/// The options string is a strftime format string, with extensions:
+///   - %L is millis: 000-999
+///   - %f is micros: 000000-999999
+///   - %N is nanos: 000000000 - 999999999
+///
+/// If no options are given, the default format is "%Y-%m-%d %H:%M:%S.%N".
+template <>
+struct format_provider<sys::TimePoint<>> {
+  static void format(const sys::TimePoint<> &TP, llvm::raw_ostream &OS,
+                     StringRef Style);
+};
+
+/// Implementation of format_provider<T> for duration types.
+///
+/// The options string of a duration  type has the grammar:
+///
+///   duration_options  ::= [unit][show_unit [number_options]]
+///   unit              ::= `h`|`m`|`s`|`ms|`us`|`ns`
+///   show_unit         ::= `+` | `-`
+///   number_options    ::= options string for a integral or floating point type
+///
+///   Examples
+///   =================================
+///   |  options  | Input | Output    |
+///   =================================
+///   | ""        | 1s    | 1 s       |
+///   | "ms"      | 1s    | 1000 ms   |
+///   | "ms-"     | 1s    | 1000      |
+///   | "ms-n"    | 1s    | 1,000     |
+///   | ""        | 1.0s  | 1.00 s    |
+///   =================================
+///
+///  If the unit of the duration type is not one of the units specified above,
+///  it is still possible to format it, provided you explicitly request a
+///  display unit or you request that the unit is not displayed.
+
+namespace detail {
+template <typename Period> struct unit { static const char value[]; };
+template <typename Period> const char unit<Period>::value[] = "";
+
+template <> struct unit<std::ratio<3600>> { static const char value[]; };
+template <> struct unit<std::ratio<60>> { static const char value[]; };
+template <> struct unit<std::ratio<1>> { static const char value[]; };
+template <> struct unit<std::milli> { static const char value[]; };
+template <> struct unit<std::micro> { static const char value[]; };
+template <> struct unit<std::nano> { static const char value[]; };
+} // namespace detail
+
+template <typename Rep, typename Period>
+struct format_provider<std::chrono::duration<Rep, Period>> {
+private:
+  typedef std::chrono::duration<Rep, Period> Dur;
+  typedef typename std::conditional<
+      std::chrono::treat_as_floating_point<Rep>::value, double, intmax_t>::type
+      InternalRep;
+
+  template <typename AsPeriod> static InternalRep getAs(const Dur &D) {
+    using namespace std::chrono;
+    return duration_cast<duration<InternalRep, AsPeriod>>(D).count();
+  }
+
+  static std::pair<InternalRep, StringRef> consumeUnit(StringRef &Style,
+                                                        const Dur &D) {
+    using namespace std::chrono;
+    if (Style.consume_front("ns"))
+      return {getAs<std::nano>(D), "ns"};
+    if (Style.consume_front("us"))
+      return {getAs<std::micro>(D), "us"};
+    if (Style.consume_front("ms"))
+      return {getAs<std::milli>(D), "ms"};
+    if (Style.consume_front("s"))
+      return {getAs<std::ratio<1>>(D), "s"};
+    if (Style.consume_front("m"))
+      return {getAs<std::ratio<60>>(D), "m"};
+    if (Style.consume_front("h"))
+      return {getAs<std::ratio<3600>>(D), "h"};
+    return {D.count(), detail::unit<Period>::value};
+  }
+
+  static bool consumeShowUnit(StringRef &Style) {
+    if (Style.empty())
+      return true;
+    if (Style.consume_front("-"))
+      return false;
+    if (Style.consume_front("+"))
+      return true;
+    assert(0 && "Unrecognised duration format");
+    return true;
+  }
+
+public:
+  static void format(const Dur &D, llvm::raw_ostream &Stream, StringRef Style) {
+    InternalRep count;
+    StringRef unit;
+    std::tie(count, unit) = consumeUnit(Style, D);
+    bool show_unit = consumeShowUnit(Style);
+
+    format_provider<InternalRep>::format(count, Stream, Style);
+
+    if (show_unit) {
+      assert(!unit.empty());
+      Stream << " " << unit;
+    }
+  }
+};
+
+} // namespace llvm
+
+#endif // LLVM_SUPPORT_CHRONO_H