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, 109 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/Support/Regex.h b/third_party/llvm-project/include/llvm/Support/Regex.h
new file mode 100644
index 000000000..b2620ab4c
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/Support/Regex.h
@@ -0,0 +1,109 @@
+//===-- Regex.h - Regular Expression matcher implementation -*- 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 implements a POSIX regular expression matcher.  Both Basic and
+// Extended POSIX regular expressions (ERE) are supported.  EREs were extended
+// to support backreferences in matches.
+// This implementation also supports matching strings with embedded NUL chars.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_REGEX_H
+#define LLVM_SUPPORT_REGEX_H
+
+#include <string>
+
+struct llvm_regex;
+
+namespace llvm {
+  class StringRef;
+  template<typename T> class SmallVectorImpl;
+
+  class Regex {
+  public:
+    enum {
+      NoFlags=0,
+      /// Compile for matching that ignores upper/lower case distinctions.
+      IgnoreCase=1,
+      /// Compile for newline-sensitive matching. With this flag '[^' bracket
+      /// expressions and '.' never match newline. A ^ anchor matches the
+      /// null string after any newline in the string in addition to its normal
+      /// function, and the $ anchor matches the null string before any
+      /// newline in the string in addition to its normal function.
+      Newline=2,
+      /// By default, the POSIX extended regular expression (ERE) syntax is
+      /// assumed. Pass this flag to turn on basic regular expressions (BRE)
+      /// instead.
+      BasicRegex=4
+    };
+
+    Regex();
+    /// Compiles the given regular expression \p Regex.
+    ///
+    /// \param Regex - referenced string is no longer needed after this
+    /// constructor does finish.  Only its compiled form is kept stored.
+    Regex(StringRef Regex, unsigned Flags = NoFlags);
+    Regex(const Regex &) = delete;
+    Regex &operator=(Regex regex) {
+      std::swap(preg, regex.preg);
+      std::swap(error, regex.error);
+      return *this;
+    }
+    Regex(Regex &&regex);
+    ~Regex();
+
+    /// isValid - returns the error encountered during regex compilation, if
+    /// any.
+    bool isValid(std::string &Error) const;
+    bool isValid() const { return !error; }
+
+    /// getNumMatches - In a valid regex, return the number of parenthesized
+    /// matches it contains.  The number filled in by match will include this
+    /// many entries plus one for the whole regex (as element 0).
+    unsigned getNumMatches() const;
+
+    /// matches - Match the regex against a given \p String.
+    ///
+    /// \param Matches - If given, on a successful match this will be filled in
+    /// with references to the matched group expressions (inside \p String),
+    /// the first group is always the entire pattern.
+    ///
+    /// \param Error - If non-null, any errors in the matching will be recorded
+    /// as a non-empty string. If there is no error, it will be an empty string.
+    ///
+    /// This returns true on a successful match.
+    bool match(StringRef String, SmallVectorImpl<StringRef> *Matches = nullptr,
+               std::string *Error = nullptr) const;
+
+    /// sub - Return the result of replacing the first match of the regex in
+    /// \p String with the \p Repl string. Backreferences like "\0" in the
+    /// replacement string are replaced with the appropriate match substring.
+    ///
+    /// Note that the replacement string has backslash escaping performed on
+    /// it. Invalid backreferences are ignored (replaced by empty strings).
+    ///
+    /// \param Error If non-null, any errors in the substitution (invalid
+    /// backreferences, trailing backslashes) will be recorded as a non-empty
+    /// string. If there is no error, it will be an empty string.
+    std::string sub(StringRef Repl, StringRef String,
+                    std::string *Error = nullptr) const;
+
+    /// If this function returns true, ^Str$ is an extended regular
+    /// expression that matches Str and only Str.
+    static bool isLiteralERE(StringRef Str);
+
+    /// Turn String into a regex by escaping its special characters.
+    static std::string escape(StringRef String);
+
+  private:
+    struct llvm_regex *preg;
+    int error;
+  };
+}
+
+#endif // LLVM_SUPPORT_REGEX_H