[msf] Make FPM reader use MappedBlockStream.

MappedBlockSTream can work with any sequence of block data where
the ordering is specified by a list of block numbers.  So rather
than manually stitch them together in the case of the FPM, reuse
this functionality so that we can treat the FPM as if it were
contiguous.

Reviewed By: ruiu
Differential Revision: https://reviews.llvm.org/D23066

llvm-svn: 277609

1 files changed, 13 insertions, 17 deletions

diff --git a/llvm/lib/DebugInfo/PDB/Raw/PDBFile.cpp b/llvm/lib/DebugInfo/PDB/Raw/PDBFile.cpp
index 8520408ebd3..75840b0e776 100644
--- a/llvm/lib/DebugInfo/PDB/Raw/PDBFile.cpp
+++ b/llvm/lib/DebugInfo/PDB/Raw/PDBFile.cpp
@@ -122,7 +122,6 @@ Error PDBFile::parseFileHeaders() {
 
   // Initialize Free Page Map.
   ContainerLayout.FreePageMap.resize(SB->NumBlocks);
-  ArrayRef<uint8_t> FpmBytes;
   // The Fpm exists either at block 1 or block 2 of the MSF.  However, this
   // allows for a maximum of getBlockSize() * 8 blocks bits in the Fpm, and
   // thusly an equal number of total blocks in the file.  For a block size
@@ -136,25 +135,22 @@ Error PDBFile::parseFileHeaders() {
   // at getBlockSize() intervals, so we have to be compatible.
   // See the function fpmPn() for more information:
   // https://github.com/Microsoft/microsoft-pdb/blob/master/PDB/msf/msf.cpp#L489
-
-  uint32_t BlocksPerSection = getBlockSize();
-  uint64_t FpmBlockOffset = SB->FreeBlockMapBlock;
+  auto FpmStream = MappedBlockStream::createFpmStream(ContainerLayout, *Buffer);
+  StreamReader FpmReader(*FpmStream);
+  ArrayRef<uint8_t> FpmBytes;
+  if (auto EC = FpmReader.readBytes(FpmBytes,
+                                    msf::getFullFpmByteSize(ContainerLayout)))
+    return EC;
   uint32_t BlocksRemaining = getBlockCount();
-  for (uint32_t SI = 0; BlocksRemaining > 0; ++SI) {
-    uint32_t FpmFileOffset = FpmBlockOffset * getBlockSize();
-
-    if (auto EC = Buffer->readBytes(FpmFileOffset, getBlockSize(), FpmBytes))
-      return EC;
-
-    uint32_t BlocksThisSection = std::min(BlocksRemaining, BlocksPerSection);
-    for (uint32_t I = 0; I < BlocksThisSection; ++I) {
-      uint32_t BI = I + BlocksPerSection * SI;
-
-      if (FpmBytes[I / 8] & (1 << (I % 8)))
+  uint32_t BI = 0;
+  for (auto Byte : FpmBytes) {
+    uint32_t BlocksThisByte = std::min(BlocksRemaining, 8U);
+    for (uint32_t I = 0; I < BlocksThisByte; ++I) {
+      if (Byte & (1 << I))
         ContainerLayout.FreePageMap[BI] = true;
+      --BlocksRemaining;
+      ++BI;
     }
-    BlocksRemaining -= BlocksThisSection;
-    FpmBlockOffset += BlocksPerSection;
   }
 
   Reader.setOffset(getBlockMapOffset());