Index: COFF/PDB.cpp
===================================================================
--- COFF/PDB.cpp
+++ COFF/PDB.cpp
@@ -85,7 +85,12 @@
 public:
   PDBLinker(SymbolTable *Symtab)
       : Alloc(), Symtab(Symtab), Builder(Alloc), TypeTable(Alloc),
-        IDTable(Alloc), GlobalTypeTable(Alloc), GlobalIDTable(Alloc) {}
+        IDTable(Alloc), GlobalTypeTable(Alloc), GlobalIDTable(Alloc) {
+    // This isn't strictly necessary, but link.exe usually puts an empty string
+    // as the first "valid" string in the string table, so we do the same in
+    // order to maintain as much byte-for-byte compatibility as possible.
+    PDBStrTab.insert("");
+  }
 
   /// Emit the basic PDB structure: initial streams, headers, etc.
   void initialize(const llvm::codeview::DebugInfo &BuildId);
@@ -1066,7 +1071,6 @@
   pdb::DbiStreamBuilder &DbiBuilder = Builder.getDbiBuilder();
   DbiBuilder.setAge(BuildId.PDB70.Age);
   DbiBuilder.setVersionHeader(pdb::PdbDbiV70);
-  ExitOnErr(DbiBuilder.addDbgStream(pdb::DbgHeaderType::NewFPO, {}));
 }
 
 void PDBLinker::addSectionContrib(pdb::DbiModuleDescriptorBuilder &LinkerModule,
Index: test/COFF/pdb-diff.test
===================================================================
--- test/COFF/pdb-diff.test
+++ test/COFF/pdb-diff.test
@@ -1,215 +0,0 @@
-This test verifies that we produce PDBs compatible with MSVC in various ways.
-We check in a cl-generated object file, PDB, and original source which serve
-as the "baseline" for us to measure against.  Then we link the same object
-file with LLD and compare the two PDBs.  Since the baseline object file and
-PDB are already checked in, we just run LLD on the object file.
-
-RUN: rm -f %T/pdb-diff-lld.pdb %T/pdb-diff-lld.exe
-RUN: lld-link /debug /pdb:%T/pdb-diff-lld.pdb /out:%T/pdb-diff-lld.exe /nodefaultlib \
-RUN:   /entry:main %S/Inputs/pdb-diff.obj
-RUN: llvm-pdbutil diff -result -values=false -left-bin-root=%S -right-bin-root=D:/src/llvm-mono/lld/test/COFF/ \
-RUN:   %T/pdb-diff-lld.pdb %S/Inputs/pdb-diff-cl.pdb | FileCheck %s
-
-CHECK:        ----------------------
-CHECK-NEXT:   |  MSF Super Block   |
-CHECK-NEXT:   |----------------+---|
-CHECK-NEXT:   |           File |   |
-CHECK-NEXT:   |----------------+---|
-CHECK-NEXT:   |     Block Size | I |
-CHECK-NEXT:   |----------------+---|
-CHECK-NEXT:   |    Block Count |
-CHECK-NEXT:   |----------------+---|
-CHECK-NEXT:   |      Unknown 1 | I |
-CHECK-NEXT:   |----------------+---|
-CHECK-NEXT:   | Directory Size |
-CHECK-NEXT:   |----------------+---|
-CHECK-NEXT:   ------------------------------------
-CHECK-NEXT:   |         Stream Directory         |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                         File |   |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                 Stream Count | I |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |            Old MSF Directory | I |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                   PDB Stream | I |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                   TPI Stream | I |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                   DBI Stream | I |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                   IPI Stream | I |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                 New FPO Data | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |          Section Header Data | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |        Named Stream "/names" | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |     Named Stream "/LinkInfo" | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   | Module "Inputs\pdb-diff.obj" | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |          Module "* Linker *" | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                     TPI Hash | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                     IPI Hash | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |           Public Symbol Hash | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |           Global Symbol Hash | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |               Symbol Records | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   ------------------------------------
-CHECK-NEXT:   |           String Table           |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                         File |   |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |            Number of Strings | D |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                 Hash Version | I |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                    Byte Size |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                    Signature | I |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |                Empty Strings |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |  {{.*}}pdb-diff.cpp | {{[EI]}} |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |  $T0 $ebp = $...p $T0 8 + =  | D |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   |  d:\src\llvm-...er internal) | D |
-CHECK-NEXT:   |------------------------------+---|
-CHECK-NEXT:   ----------------------------
-CHECK-NEXT:   |        PDB Stream        |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |                 File |   |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |          Stream Size |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |                  Age | I |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |                 Guid | D |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |            Signature | D |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |              Version | I |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |       Features (set) | I |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |              Feature | I |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |    Named Stream Size |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |  Named Streams (map) | {{[EI]}} |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |               /names | {{[EI]}} |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   |            /LinkInfo | {{[EI]}} |
-CHECK-NEXT:   |----------------------+---|
-CHECK-NEXT:   ----------------------------------------------
-CHECK-NEXT:   |                 DBI Stream                 |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                                   File |   |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                            Dbi Version | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                                    Age | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                                Machine | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                                  Flags | D |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                            Build Major | D |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                            Build Minor | D |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                           Build Number | D |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                        PDB DLL Version | D |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                           PDB DLL RBLD | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                              DBG (FPO) | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                        DBG (Exception) | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                            DBG (Fixup) | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                        DBG (OmapToSrc) | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                      DBG (OmapFromSrc) | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                       DBG (SectionHdr) | {{[EI]}} |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                      DBG (TokenRidMap) | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                            DBG (Xdata) | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                            DBG (Pdata) | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                           DBG (NewFPO) | {{[EI]}} |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                   DBG (SectionHdrOrig) | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                         Globals Stream | {{[EI]}} |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                         Publics Stream | {{[EI]}} |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                         Symbol Records | {{[EI]}} |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                             Has CTypes | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                Is Incrementally Linked | D |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                            Is Stripped | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                           Module Count | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                      Source File Count | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   | Module "Inputs\pdb-diff.obj" |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                                 - Modi | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                        - Obj File Name | {{[EI]}} |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                         - Debug Stream | {{[EI]}} |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                        - C11 Byte Size | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                        - C13 Byte Size | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                           - # of files | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                  - Pdb File Path Index | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |               - Source File Name Index | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                     - Symbol Byte Size |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |            Module "* Linker *"             |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                                 - Modi | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                        - Obj File Name | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                         - Debug Stream | {{[EI]}} |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                        - C11 Byte Size | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                        - C13 Byte Size | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                           - # of files | I |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                  - Pdb File Path Index | {{[EI]}} |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |               - Source File Name Index | {{[EI]}} |
-CHECK-NEXT:   |----------------------------------------+---|
-CHECK-NEXT:   |                     - Symbol Byte Size |
-CHECK-NEXT:   |----------------------------------------+---|
-
-
Index: test/COFF/pdb-file-static.test
===================================================================
--- test/COFF/pdb-file-static.test
+++ test/COFF/pdb-file-static.test
@@ -43,9 +43,9 @@
 # CHECK: ============================================================
 # CHECK-LABEL:   Mod 0000 | `{{.*}}a.obj`:
 # CHECK:              232 | S_FILESTATIC [size = 16] `x`
-# CHECK-NEXT:               type = 0x0074 (int), file name = 1 (D:\src\llvmbuild\cl\Debug\x64\a.obj), flags = enreg global | enreg static
+# CHECK-NEXT:               type = 0x0074 (int), file name = 2 (D:\src\llvmbuild\cl\Debug\x64\a.obj), flags = enreg global | enreg static
 # CHECK:         Mod 0001 | `{{.*}}b.obj`:
 # CHECK:              232 | S_FILESTATIC [size = 16] `y`
-# CHECK-NEXT:               type = 0x0074 (int), file name = 73 (D:\src\llvmbuild\cl\Debug\x64\b.obj), flags = enreg global | enreg static
+# CHECK-NEXT:               type = 0x0074 (int), file name = 74 (D:\src\llvmbuild\cl\Debug\x64\b.obj), flags = enreg global | enreg static
 # CHECK-LABEL:   Mod 0002 | `* Linker *`:
 
Index: test/COFF/pdb-lib.s
===================================================================
--- test/COFF/pdb-lib.s
+++ test/COFF/pdb-lib.s
@@ -13,15 +13,15 @@
 # CHECK-NEXT: ============================================================
 # CHECK-NEXT:   Mod 0000 | `{{.*pdb-lib.s.tmp[/\\]foo.obj}}`:
 # CHECK-NEXT:              Obj: `{{.*pdb-lib.s.tmp[/\\]foo.obj}}`:
-# CHECK-NEXT:              debug stream: 9, # files: 0, has ec info: false
+# CHECK-NEXT:              debug stream: 10, # files: 0, has ec info: false
 # CHECK-NEXT:              pdb file ni: 0 ``, src file ni: 0 ``
 # CHECK-NEXT:   Mod 0001 | `bar.obj`:
 # CHECK-NEXT:              Obj: `{{.*pdb-lib.s.tmp[/\\]bar.lib}}`:
-# CHECK-NEXT:              debug stream: 10, # files: 0, has ec info: false
+# CHECK-NEXT:              debug stream: 11, # files: 0, has ec info: false
 # CHECK-NEXT:              pdb file ni: 0 ``, src file ni: 0 ``
 # CHECK-NEXT:   Mod 0002 | `* Linker *`:
 # CHECK-NEXT:              Obj: ``:
-# CHECK-NEXT:              debug stream: 11, # files: 0, has ec info: false
+# CHECK-NEXT:              debug stream: 12, # files: 0, has ec info: false
 # CHECK-NEXT:              pdb file ni: 1 `{{.*foo.pdb}}`, src file ni: 0 ``
 
         .def     _main;
Index: test/COFF/pdb-linker-module.test
===================================================================
--- test/COFF/pdb-linker-module.test
+++ test/COFF/pdb-linker-module.test
@@ -4,7 +4,7 @@
 
 MODS:      Mod 0001 | `* Linker *`
 MODS-NEXT:             Obj: ``:
-MODS-NEXT:             debug stream: 10, # files: 0, has ec info: false
+MODS-NEXT:             debug stream: 12, # files: 0, has ec info: false
 MODS-NEXT:             pdb file ni: 1 `{{.*}}pdb-linker-module.test.tmp.pdb`, src file ni: 0 ``
 
 SYMS:      Mod 0001 | `* Linker *`
Index: test/COFF/pdb-same-name.test
===================================================================
--- test/COFF/pdb-same-name.test
+++ test/COFF/pdb-same-name.test
@@ -15,9 +15,9 @@
 RAW-NEXT: ============================================================
 RAW-NEXT:   Mod 0000 | `foo.obj`:
 RAW-NEXT:              Obj: `{{.*}}1\foo.lib`:
-RAW-NEXT:              debug stream: 9, # files: 1, has ec info: false
+RAW-NEXT:              debug stream: 11, # files: 1, has ec info: false
 RAW-NEXT:              pdb file ni: 0 ``, src file ni: 0 ``
 RAW-NEXT:   Mod 0001 | `foo.obj`:
 RAW-NEXT:              Obj: `{{.*}}2\foo.lib`:
-RAW-NEXT:              debug stream: 10, # files: 1, has ec info: false
+RAW-NEXT:              debug stream: 12, # files: 1, has ec info: false
 RAW-NEXT:              pdb file ni: 0 ``, src file ni: 0 ``
Index: test/COFF/pdb.test
===================================================================
--- test/COFF/pdb.test
+++ test/COFF/pdb.test
@@ -121,15 +121,15 @@
 RAW-NEXT: ============================================================
 RAW-NEXT:   Mod 0000 | `{{.*}}pdb.test.tmp1.obj`:
 RAW-NEXT:              Obj: `{{.*}}pdb.test.tmp1.obj`:
-RAW-NEXT:              debug stream: 9, # files: 1, has ec info: false
+RAW-NEXT:              debug stream: 11, # files: 1, has ec info: false
 RAW-NEXT:              pdb file ni: 0 ``, src file ni: 0 ``
 RAW-NEXT:   Mod 0001 | `{{.*}}pdb.test.tmp2.obj`:
 RAW-NEXT:              Obj: `{{.*}}pdb.test.tmp2.obj`:
-RAW-NEXT:              debug stream: 10, # files: 1, has ec info: false
+RAW-NEXT:              debug stream: 12, # files: 1, has ec info: false
 RAW-NEXT:              pdb file ni: 0 ``, src file ni: 0 ``
 RAW-NEXT:   Mod 0002 | `* Linker *`:
 RAW-NEXT:              Obj: ``:
-RAW-NEXT:              debug stream: 11, # files: 0, has ec info: false
+RAW-NEXT:              debug stream: 13, # files: 0, has ec info: false
 RAW-NEXT:              pdb file ni: 1 `{{.*pdb.test.tmp.pdb}}`, src file ni: 0 ``
 RAW:                          Types (TPI Stream)
 RAW-NEXT: ============================================================