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, 261 insertions, 0 deletions

diff --git a/third_party/llvm-project/StringMap.cpp b/third_party/llvm-project/StringMap.cpp
new file mode 100644
index 000000000..6b5ea020d
--- /dev/null
+++ b/third_party/llvm-project/StringMap.cpp
@@ -0,0 +1,261 @@
+//===--- StringMap.cpp - String Hash table map implementation -------------===//
+//
+// 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 the StringMap class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/DJB.h"
+#include "llvm/Support/MathExtras.h"
+#include <cassert>
+
+using namespace llvm;
+
+/// Returns the number of buckets to allocate to ensure that the DenseMap can
+/// accommodate \p NumEntries without need to grow().
+static unsigned getMinBucketToReserveForEntries(unsigned NumEntries) {
+  // Ensure that "NumEntries * 4 < NumBuckets * 3"
+  if (NumEntries == 0)
+    return 0;
+  // +1 is required because of the strict equality.
+  // For example if NumEntries is 48, we need to return 401.
+  return NextPowerOf2(NumEntries * 4 / 3 + 1);
+}
+
+StringMapImpl::StringMapImpl(unsigned InitSize, unsigned itemSize) {
+  ItemSize = itemSize;
+
+  // If a size is specified, initialize the table with that many buckets.
+  if (InitSize) {
+    // The table will grow when the number of entries reach 3/4 of the number of
+    // buckets. To guarantee that "InitSize" number of entries can be inserted
+    // in the table without growing, we allocate just what is needed here.
+    init(getMinBucketToReserveForEntries(InitSize));
+    return;
+  }
+
+  // Otherwise, initialize it with zero buckets to avoid the allocation.
+  TheTable = nullptr;
+  NumBuckets = 0;
+  NumItems = 0;
+  NumTombstones = 0;
+}
+
+void StringMapImpl::init(unsigned InitSize) {
+  assert((InitSize & (InitSize-1)) == 0 &&
+         "Init Size must be a power of 2 or zero!");
+
+  unsigned NewNumBuckets = InitSize ? InitSize : 16;
+  NumItems = 0;
+  NumTombstones = 0;
+
+  TheTable = static_cast<StringMapEntryBase **>(
+      safe_calloc(NewNumBuckets+1,
+                  sizeof(StringMapEntryBase **) + sizeof(unsigned)));
+
+  // Set the member only if TheTable was successfully allocated
+  NumBuckets = NewNumBuckets;
+
+  // Allocate one extra bucket, set it to look filled so the iterators stop at
+  // end.
+  TheTable[NumBuckets] = (StringMapEntryBase*)2;
+}
+
+/// LookupBucketFor - Look up the bucket that the specified string should end
+/// up in.  If it already exists as a key in the map, the Item pointer for the
+/// specified bucket will be non-null.  Otherwise, it will be null.  In either
+/// case, the FullHashValue field of the bucket will be set to the hash value
+/// of the string.
+unsigned StringMapImpl::LookupBucketFor(StringRef Name) {
+  unsigned HTSize = NumBuckets;
+  if (HTSize == 0) {  // Hash table unallocated so far?
+    init(16);
+    HTSize = NumBuckets;
+  }
+  unsigned FullHashValue = djbHash(Name, 0);
+  unsigned BucketNo = FullHashValue & (HTSize-1);
+  unsigned *HashTable = (unsigned *)(TheTable + NumBuckets + 1);
+
+  unsigned ProbeAmt = 1;
+  int FirstTombstone = -1;
+  while (true) {
+    StringMapEntryBase *BucketItem = TheTable[BucketNo];
+    // If we found an empty bucket, this key isn't in the table yet, return it.
+    if (LLVM_LIKELY(!BucketItem)) {
+      // If we found a tombstone, we want to reuse the tombstone instead of an
+      // empty bucket.  This reduces probing.
+      if (FirstTombstone != -1) {
+        HashTable[FirstTombstone] = FullHashValue;
+        return FirstTombstone;
+      }
+
+      HashTable[BucketNo] = FullHashValue;
+      return BucketNo;
+    }
+
+    if (BucketItem == getTombstoneVal()) {
+      // Skip over tombstones.  However, remember the first one we see.
+      if (FirstTombstone == -1) FirstTombstone = BucketNo;
+    } else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
+      // If the full hash value matches, check deeply for a match.  The common
+      // case here is that we are only looking at the buckets (for item info
+      // being non-null and for the full hash value) not at the items.  This
+      // is important for cache locality.
+
+      // Do the comparison like this because Name isn't necessarily
+      // null-terminated!
+      char *ItemStr = (char*)BucketItem+ItemSize;
+      if (Name == StringRef(ItemStr, BucketItem->getKeyLength())) {
+        // We found a match!
+        return BucketNo;
+      }
+    }
+
+    // Okay, we didn't find the item.  Probe to the next bucket.
+    BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
+
+    // Use quadratic probing, it has fewer clumping artifacts than linear
+    // probing and has good cache behavior in the common case.
+    ++ProbeAmt;
+  }
+}
+
+/// FindKey - Look up the bucket that contains the specified key. If it exists
+/// in the map, return the bucket number of the key.  Otherwise return -1.
+/// This does not modify the map.
+int StringMapImpl::FindKey(StringRef Key) const {
+  unsigned HTSize = NumBuckets;
+  if (HTSize == 0) return -1;  // Really empty table?
+  unsigned FullHashValue = djbHash(Key, 0);
+  unsigned BucketNo = FullHashValue & (HTSize-1);
+  unsigned *HashTable = (unsigned *)(TheTable + NumBuckets + 1);
+
+  unsigned ProbeAmt = 1;
+  while (true) {
+    StringMapEntryBase *BucketItem = TheTable[BucketNo];
+    // If we found an empty bucket, this key isn't in the table yet, return.
+    if (LLVM_LIKELY(!BucketItem))
+      return -1;
+
+    if (BucketItem == getTombstoneVal()) {
+      // Ignore tombstones.
+    } else if (LLVM_LIKELY(HashTable[BucketNo] == FullHashValue)) {
+      // If the full hash value matches, check deeply for a match.  The common
+      // case here is that we are only looking at the buckets (for item info
+      // being non-null and for the full hash value) not at the items.  This
+      // is important for cache locality.
+
+      // Do the comparison like this because NameStart isn't necessarily
+      // null-terminated!
+      char *ItemStr = (char*)BucketItem+ItemSize;
+      if (Key == StringRef(ItemStr, BucketItem->getKeyLength())) {
+        // We found a match!
+        return BucketNo;
+      }
+    }
+
+    // Okay, we didn't find the item.  Probe to the next bucket.
+    BucketNo = (BucketNo+ProbeAmt) & (HTSize-1);
+
+    // Use quadratic probing, it has fewer clumping artifacts than linear
+    // probing and has good cache behavior in the common case.
+    ++ProbeAmt;
+  }
+}
+
+/// RemoveKey - Remove the specified StringMapEntry from the table, but do not
+/// delete it.  This aborts if the value isn't in the table.
+void StringMapImpl::RemoveKey(StringMapEntryBase *V) {
+  const char *VStr = (char*)V + ItemSize;
+  StringMapEntryBase *V2 = RemoveKey(StringRef(VStr, V->getKeyLength()));
+  (void)V2;
+  assert(V == V2 && "Didn't find key?");
+}
+
+/// RemoveKey - Remove the StringMapEntry for the specified key from the
+/// table, returning it.  If the key is not in the table, this returns null.
+StringMapEntryBase *StringMapImpl::RemoveKey(StringRef Key) {
+  int Bucket = FindKey(Key);
+  if (Bucket == -1) return nullptr;
+
+  StringMapEntryBase *Result = TheTable[Bucket];
+  TheTable[Bucket] = getTombstoneVal();
+  --NumItems;
+  ++NumTombstones;
+  assert(NumItems + NumTombstones <= NumBuckets);
+
+  return Result;
+}
+
+/// RehashTable - Grow the table, redistributing values into the buckets with
+/// the appropriate mod-of-hashtable-size.
+unsigned StringMapImpl::RehashTable(unsigned BucketNo) {
+  unsigned NewSize;
+  unsigned *HashTable = (unsigned *)(TheTable + NumBuckets + 1);
+
+  // If the hash table is now more than 3/4 full, or if fewer than 1/8 of
+  // the buckets are empty (meaning that many are filled with tombstones),
+  // grow/rehash the table.
+  if (LLVM_UNLIKELY(NumItems * 4 > NumBuckets * 3)) {
+    NewSize = NumBuckets*2;
+  } else if (LLVM_UNLIKELY(NumBuckets - (NumItems + NumTombstones) <=
+                           NumBuckets / 8)) {
+    NewSize = NumBuckets;
+  } else {
+    return BucketNo;
+  }
+
+  unsigned NewBucketNo = BucketNo;
+  // Allocate one extra bucket which will always be non-empty.  This allows the
+  // iterators to stop at end.
+  auto NewTableArray = static_cast<StringMapEntryBase **>(
+      safe_calloc(NewSize+1, sizeof(StringMapEntryBase *) + sizeof(unsigned)));
+
+  unsigned *NewHashArray = (unsigned *)(NewTableArray + NewSize + 1);
+  NewTableArray[NewSize] = (StringMapEntryBase*)2;
+
+  // Rehash all the items into their new buckets.  Luckily :) we already have
+  // the hash values available, so we don't have to rehash any strings.
+  for (unsigned I = 0, E = NumBuckets; I != E; ++I) {
+    StringMapEntryBase *Bucket = TheTable[I];
+    if (Bucket && Bucket != getTombstoneVal()) {
+      // Fast case, bucket available.
+      unsigned FullHash = HashTable[I];
+      unsigned NewBucket = FullHash & (NewSize-1);
+      if (!NewTableArray[NewBucket]) {
+        NewTableArray[FullHash & (NewSize-1)] = Bucket;
+        NewHashArray[FullHash & (NewSize-1)] = FullHash;
+        if (I == BucketNo)
+          NewBucketNo = NewBucket;
+        continue;
+      }
+
+      // Otherwise probe for a spot.
+      unsigned ProbeSize = 1;
+      do {
+        NewBucket = (NewBucket + ProbeSize++) & (NewSize-1);
+      } while (NewTableArray[NewBucket]);
+
+      // Finally found a slot.  Fill it in.
+      NewTableArray[NewBucket] = Bucket;
+      NewHashArray[NewBucket] = FullHash;
+      if (I == BucketNo)
+        NewBucketNo = NewBucket;
+    }
+  }
+
+  free(TheTable);
+
+  TheTable = NewTableArray;
+  NumBuckets = NewSize;
+  NumTombstones = 0;
+  return NewBucketNo;
+}