[PDB] Hash types up front when merging types instead of using StringMap

Summary:
First, StringMap uses llvm::HashString, which is only good for short
identifiers and really bad for large blobs of binary data like type
records. Moving to `DenseMap<StringRef, TypeIndex>` with some tricks for
memory allocation fixes that.

Unfortunately, that didn't buy very much performance. Profiling showed
that we spend a long time during DenseMap growth rehashing existing
entries. Also, in general, DenseMap is faster when the keys are small.
This change takes that to the logical conclusion by introducing a small
wrapper value type around a pointer to key data. The key data contains a
precomputed hash, the original record data (pointer and size), and the
type index, which is the "value" of our original map.

This reduces the time to produce llvm-as.exe and llvm-as.pdb from ~15s
on my machine to 3.5s, which is about a 4x improvement.

Reviewers: zturner, inglorion, ruiu

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33428

llvm-svn: 303665

1 files changed, 6 insertions, 8 deletions

diff --git a/llvm/tools/llvm-pdbdump/llvm-pdbdump.cpp b/llvm/tools/llvm-pdbdump/llvm-pdbdump.cpp
index 6b6a0ef046a..64688559323 100644
--- a/llvm/tools/llvm-pdbdump/llvm-pdbdump.cpp
+++ b/llvm/tools/llvm-pdbdump/llvm-pdbdump.cpp
@@ -877,14 +877,12 @@ static void mergePdbs() {
 
   auto &DestTpi = Builder.getTpiBuilder();
   auto &DestIpi = Builder.getIpiBuilder();
-  MergedTpi.ForEachRecord(
-      [&DestTpi](TypeIndex TI, MutableArrayRef<uint8_t> Data) {
-        DestTpi.addTypeRecord(Data, None);
-      });
-  MergedIpi.ForEachRecord(
-      [&DestIpi](TypeIndex TI, MutableArrayRef<uint8_t> Data) {
-        DestIpi.addTypeRecord(Data, None);
-      });
+  MergedTpi.ForEachRecord([&DestTpi](TypeIndex TI, ArrayRef<uint8_t> Data) {
+    DestTpi.addTypeRecord(Data, None);
+  });
+  MergedIpi.ForEachRecord([&DestIpi](TypeIndex TI, ArrayRef<uint8_t> Data) {
+    DestIpi.addTypeRecord(Data, None);
+  });
 
   SmallString<64> OutFile(opts::merge::PdbOutputFile);
   if (OutFile.empty()) {