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, 126 insertions, 0 deletions

diff --git a/third_party/llvm-project/include/llvm/Support/Debug.h b/third_party/llvm-project/include/llvm/Support/Debug.h
new file mode 100644
index 000000000..64b730951
--- /dev/null
+++ b/third_party/llvm-project/include/llvm/Support/Debug.h
@@ -0,0 +1,126 @@
+//===- llvm/Support/Debug.h - Easy way to add debug output ------*- 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 handy way of adding debugging information to your
+// code, without it being enabled all of the time, and without having to add
+// command line options to enable it.
+//
+// In particular, just wrap your code with the LLVM_DEBUG() macro, and it will
+// be enabled automatically if you specify '-debug' on the command-line.
+// LLVM_DEBUG() requires the DEBUG_TYPE macro to be defined. Set it to "foo"
+// specify that your debug code belongs to class "foo". Be careful that you only
+// do this after including Debug.h and not around any #include of headers.
+// Headers should define and undef the macro acround the code that needs to use
+// the LLVM_DEBUG() macro. Then, on the command line, you can specify
+// '-debug-only=foo' to enable JUST the debug information for the foo class.
+//
+// When compiling without assertions, the -debug-* options and all code in
+// LLVM_DEBUG() statements disappears, so it does not affect the runtime of the
+// code.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_DEBUG_H
+#define LLVM_SUPPORT_DEBUG_H
+
+namespace llvm {
+
+class raw_ostream;
+
+#ifndef NDEBUG
+
+/// isCurrentDebugType - Return true if the specified string is the debug type
+/// specified on the command line, or if none was specified on the command line
+/// with the -debug-only=X option.
+///
+bool isCurrentDebugType(const char *Type);
+
+/// setCurrentDebugType - Set the current debug type, as if the -debug-only=X
+/// option were specified.  Note that DebugFlag also needs to be set to true for
+/// debug output to be produced.
+///
+void setCurrentDebugType(const char *Type);
+
+/// setCurrentDebugTypes - Set the current debug type, as if the
+/// -debug-only=X,Y,Z option were specified. Note that DebugFlag
+/// also needs to be set to true for debug output to be produced.
+///
+void setCurrentDebugTypes(const char **Types, unsigned Count);
+
+/// DEBUG_WITH_TYPE macro - This macro should be used by passes to emit debug
+/// information.  In the '-debug' option is specified on the commandline, and if
+/// this is a debug build, then the code specified as the option to the macro
+/// will be executed.  Otherwise it will not be.  Example:
+///
+/// DEBUG_WITH_TYPE("bitset", dbgs() << "Bitset contains: " << Bitset << "\n");
+///
+/// This will emit the debug information if -debug is present, and -debug-only
+/// is not specified, or is specified as "bitset".
+#define DEBUG_WITH_TYPE(TYPE, X)                                        \
+  do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType(TYPE)) { X; } \
+  } while (false)
+
+#else
+#define isCurrentDebugType(X) (false)
+#define setCurrentDebugType(X)
+#define setCurrentDebugTypes(X, N)
+#define DEBUG_WITH_TYPE(TYPE, X) do { } while (false)
+#endif
+
+/// This boolean is set to true if the '-debug' command line option
+/// is specified.  This should probably not be referenced directly, instead, use
+/// the DEBUG macro below.
+///
+extern bool DebugFlag;
+
+/// \name Verification flags.
+///
+/// These flags turns on/off that are expensive and are turned off by default,
+/// unless macro EXPENSIVE_CHECKS is defined. The flags allow selectively
+/// turning the checks on without need to recompile.
+/// \{
+
+/// Enables verification of dominator trees.
+///
+extern bool VerifyDomInfo;
+
+/// Enables verification of loop info.
+///
+extern bool VerifyLoopInfo;
+
+/// Enables verification of MemorySSA.
+///
+extern bool VerifyMemorySSA;
+
+///\}
+
+/// EnableDebugBuffering - This defaults to false.  If true, the debug
+/// stream will install signal handlers to dump any buffered debug
+/// output.  It allows clients to selectively allow the debug stream
+/// to install signal handlers if they are certain there will be no
+/// conflict.
+///
+extern bool EnableDebugBuffering;
+
+/// dbgs() - This returns a reference to a raw_ostream for debugging
+/// messages.  If debugging is disabled it returns errs().  Use it
+/// like: dbgs() << "foo" << "bar";
+raw_ostream &dbgs();
+
+// DEBUG macro - This macro should be used by passes to emit debug information.
+// In the '-debug' option is specified on the commandline, and if this is a
+// debug build, then the code specified as the option to the macro will be
+// executed.  Otherwise it will not be.  Example:
+//
+// LLVM_DEBUG(dbgs() << "Bitset contains: " << Bitset << "\n");
+//
+#define LLVM_DEBUG(X) DEBUG_WITH_TYPE(DEBUG_TYPE, X)
+
+} // end namespace llvm
+
+#endif // LLVM_SUPPORT_DEBUG_H