pdbdump: Do not treat stream 0 pages as allocated pages.

[ruiu]

Summary

I examined a few PDBs and all of them treated pages for stream 0
are unused, thus they were unmarked in their free page bitmap.
I think we should do the same thing for compatibility.

[zturner]

tools/llvm-pdbdump/LLVMOutputStyle.cpp

315

This isn't the correct check. S here is a block number, not a stream number (Feel free to rename this to B if you want). The outer loop should be written:

for (auto &SE : File.getStreamMap().drop_front(1))

[ruiu]

• Updated as per Zach's comment.

tools/llvm-pdbdump/LLVMOutputStyle.cpp

for (uint32_t I = 0; I < NumSections; ++I) {
     uint32_t Fpm0 = 1 + BlocksPerSection * I;
     // 2 Fpm blocks spaced at `getBlockSize()` block intervals
     recordKnownUsedPage(PS, Fpm0);
     recordKnownUsedPage(PS, Fpm0 + 1);
   }
 
   recordKnownUsedPage(PS, File.getBlockMapIndex()); // Stream Table
 
-  for (auto DB : File.getDirectoryBlockArray()) {
+  for (auto DB : File.getDirectoryBlockArray())
     recordKnownUsedPage(PS, DB);
-  }
-  for (auto &SE : File.getStreamMap()) {
-    for (auto &S : SE) {
+
+  // Record pages used by streams. Note that pages for stream 0
+  // are considered being unused because that's what MSVC tools do.
+  // Stream 0 doesn't contain actual data, so it makes some sense,
+  // though it's a bit confusing to us.
+  for (auto &SE : File.getStreamMap())
+    for (auto &S : SE)
+      if (S != 0)
         recordKnownUsedPage(PS, S);
-    }
-  }
 
   dumpBitVector("Msf Free Pages", FPM);
   dumpBitVector("Orphaned Pages", PS.OrphanedPages);
   dumpBitVector("Multiply Used Pages", PS.MultiUsePages);
   dumpBitVector("Use After Free Pages", PS.UseAfterFreePages);
   return Error::success();
 }