Index: lib/DebugInfo/MSF/MSFBuilder.cpp
===================================================================
--- lib/DebugInfo/MSF/MSFBuilder.cpp
+++ lib/DebugInfo/MSF/MSFBuilder.cpp
@@ -253,6 +253,22 @@
   // grow.
   SB->NumBlocks = FreeBlocks.size();
 
+  // Allocate discontiguous free page map blocks. If one page is too
+  // small to store the entire FPM, two or more pages are allocated
+  // for the FPM.
+  uint32_t NumFPMs = alignTo(FreeBlocks.size(), BlockSize) / BlockSize;
+  for (uint32_t I = 0; I != NumFPMs; ++I) {
+    FreeBlocks[I * BlockSize + kFreePageMap0Block] = false;
+    FreeBlocks[I * BlockSize + kFreePageMap1Block] = false;
+  }
+
+  // Copy free page map. Note that on-disk FPM is slightly different from
+  // in-memory FPM since the pages for stream 0 are marked unused on-disk.
+  // We need to do that for compatibility.
+  L.FreePageMap = FreeBlocks;
+  for (uint32_t BlockNumber : StreamData[0].second)
+    L.FreePageMap[BlockNumber] = false;
+
   ulittle32_t *DirBlocks = Allocator.Allocate<ulittle32_t>(NumDirectoryBlocks);
   std::uninitialized_copy_n(DirectoryBlocks.begin(), NumDirectoryBlocks,
                             DirBlocks);
Index: lib/DebugInfo/PDB/Raw/PDBFileBuilder.cpp
===================================================================
--- lib/DebugInfo/PDB/Raw/PDBFileBuilder.cpp
+++ lib/DebugInfo/PDB/Raw/PDBFileBuilder.cpp
@@ -113,6 +113,25 @@
 
   if (auto EC = Writer.writeObject(*Layout.SB))
     return EC;
+
+  // Write free page map.
+  uint32_t BlockSize = Layout.SB->BlockSize;
+  BitVector FPM = Layout.FreePageMap;
+  FPM.resize(alignTo(FPM.size(), BlockSize), true);
+  uint32_t NumFPMBlocks = FPM.size() / BlockSize;
+  for (uint32_t I = 0; I != NumFPMBlocks; ++I) {
+    std::vector<uint8_t> Buf(Layout.SB->BlockSize);
+    for (uint32_t J = 0; J != BlockSize; ++J)
+      if (FPM[I * BlockSize + J])
+        Buf[J / 8] |= 1 << (J % 8);
+
+    uint32_t PageNum = I * BlockSize + Layout.SB->FreeBlockMapBlock;
+    Writer.setOffset(PageNum * BlockSize);
+    if (auto EC = Writer.writeArray(ArrayRef<uint8_t>(Buf)))
+      return EC;
+  }
+
+  // Write block map.
   uint32_t BlockMapOffset =
       msf::blockToOffset(Layout.SB->BlockMapAddr, Layout.SB->BlockSize);
   Writer.setOffset(BlockMapOffset);
@@ -145,4 +164,4 @@
   }
 
   return Buffer.commit();
-}
\ No newline at end of file
+}
Index: test/DebugInfo/PDB/pdbdump-fpm.test
===================================================================
--- /dev/null
+++ test/DebugInfo/PDB/pdbdump-fpm.test
@@ -0,0 +1,21 @@
+# RUN: llvm-pdbdump yaml2pdb -pdb=%t.pdb %s
+# RUN: llvm-pdbdump raw -page-stats %t.pdb | FileCheck %s
+
+# CHECK: Multiply Used Pages: []
+# CHECK: Use After Free Pages: []
+
+MSF:
+  SuperBlock:
+    BlockSize:       1024
+    FreeBlockMap:    2
+    NumBlocks:       2000
+    NumDirectoryBytes: 136
+    Unknown1:        0
+    BlockMapAddr:    24
+  NumDirectoryBlocks: 1
+  DirectoryBlocks: [ 23 ]
+  NumStreams:      1
+  FileSize:        2048000
+StreamSizes:     [ 40 ]
+StreamMap:
+  - Stream:          [ 8 ]
Index: test/DebugInfo/PDB/pdbdump-readwrite.test
===================================================================
--- test/DebugInfo/PDB/pdbdump-readwrite.test
+++ test/DebugInfo/PDB/pdbdump-readwrite.test
@@ -3,36 +3,51 @@
 RUN:   %p/Inputs/empty.pdb > %t.1
 RUN: llvm-pdbdump yaml2pdb -pdb=%t.2 %t.1
 
-RUN: llvm-pdbdump raw -headers %p/Inputs/empty.pdb | FileCheck %s
-RUN: llvm-pdbdump raw -headers %t.2 | FileCheck %s
+RUN: llvm-pdbdump raw -headers %p/Inputs/empty.pdb | FileCheck -check-prefix=HDR %s
+RUN: llvm-pdbdump raw -headers %t.2 | FileCheck -check-prefix=HDR %s
 
-CHECK:      FileHeaders {
-CHECK-NEXT:   BlockSize: 4096
-CHECK-NEXT:   FreeBlockMap: 2
-CHECK-NEXT:   NumBlocks: 25
-CHECK-NEXT:   NumDirectoryBytes: 136
-CHECK-NEXT:   Unknown1: 0
-CHECK-NEXT:   BlockMapAddr: 24
-CHECK-NEXT:   NumDirectoryBlocks: 1
-CHECK-NEXT:   DirectoryBlocks: [23]
-CHECK-NEXT:   NumStreams: 17
-CHECK-NEXT: }
-CHECK-NEXT: PDB Stream {
-CHECK-NEXT:   Version: 20000404
-CHECK-NEXT:   Signature: 0x54E507E2
-CHECK-NEXT:   Age: 1
-CHECK-NEXT:   Guid: {0B355641-86A0-A249-896F-9988FAE52FF0}
-CHECK-NEXT: }
-CHECK-NEXT: DBI Stream {
-CHECK-NEXT:   Dbi Version: 19990903
-CHECK-NEXT:   Age: 1
-CHECK-NEXT:   Incremental Linking: Yes
-CHECK-NEXT:   Has CTypes: No
-CHECK-NEXT:   Is Stripped: No
-CHECK-NEXT:   Machine Type: x86
-CHECK-NEXT:   Symbol Record Stream Index:
-CHECK-NEXT:   Public Symbol Stream Index:
-CHECK-NEXT:   Global Symbol Stream Index:
-CHECK-NEXT:   Toolchain Version: 12.0
-CHECK-NEXT:   mspdb120.dll version: 12.0.31101
-CHECK-NEXT: }
+HDR:      FileHeaders {
+HDR-NEXT:   BlockSize: 4096
+HDR-NEXT:   FreeBlockMap: 2
+HDR-NEXT:   NumBlocks: 25
+HDR-NEXT:   NumDirectoryBytes: 136
+HDR-NEXT:   Unknown1: 0
+HDR-NEXT:   BlockMapAddr: 24
+HDR-NEXT:   NumDirectoryBlocks: 1
+HDR-NEXT:   DirectoryBlocks: [23]
+HDR-NEXT:   NumStreams: 17
+HDR-NEXT: }
+HDR-NEXT: PDB Stream {
+HDR-NEXT:   Version: 20000404
+HDR-NEXT:   Signature: 0x54E507E2
+HDR-NEXT:   Age: 1
+HDR-NEXT:   Guid: {0B355641-86A0-A249-896F-9988FAE52FF0}
+HDR-NEXT: }
+HDR-NEXT: DBI Stream {
+HDR-NEXT:   Dbi Version: 19990903
+HDR-NEXT:   Age: 1
+HDR-NEXT:   Incremental Linking: Yes
+HDR-NEXT:   Has CTypes: No
+HDR-NEXT:   Is Stripped: No
+HDR-NEXT:   Machine Type: x86
+HDR-NEXT:   Symbol Record Stream Index:
+HDR-NEXT:   Public Symbol Stream Index:
+HDR-NEXT:   Global Symbol Stream Index:
+HDR-NEXT:   Toolchain Version: 12.0
+HDR-NEXT:   mspdb120.dll version: 12.0.31101
+HDR-NEXT: }
+
+RUN: llvm-pdbdump raw -page-stats %p/Inputs/empty.pdb | FileCheck -check-prefix=FPM1 %s
+RUN: llvm-pdbdump raw -page-stats %t.2 | FileCheck -check-prefix=FPM2 %s
+
+FPM1:      Msf Free Pages: [3, 4, 5, 8, 9]
+FPM1-NEXT: Orphaned Pages: []
+FPM1-NEXT: Multiply Used Pages: []
+FPM1-NEXT: Use After Free Pages: []
+
+;; We are not able to correctly restore stream 0.
+;; That's why we get a different result.
+FPM2:      Msf Free Pages: [3, 4, 5, 9]
+FPM2-NEXT: Orphaned Pages: [8]
+FPM2-NEXT: Multiply Used Pages: []
+FPM2-NEXT: Use After Free Pages: []