[PDB] Don't emit debug info associated with dead chunks

Summary:
Previously we didn't add debug info chunks to the SparseChunks array, so
they didn't participate in section GC. Now we do.

Reviewers: ruiu

Subscribers: aprantl, llvm-commits

Differential Revision: https://reviews.llvm.org/D34356

llvm-svn: 305811

lld/COFF/Chunks.h

@@ -177,6 +177,12 @@ public:
   // redundant when GC is enabled, as all comdat sections will start out dead.
   void markDiscarded() { Discarded = true; }
 
+  // True if this is a codeview debug info chunk. These will not be laid out in
+  // the image. Instead they will end up in the PDB, if one is requested.
+  bool isCodeView() const {
+    return SectionName == ".debug" || SectionName.startswith(".debug$");
+  }
+
   // Allow iteration over the bodies of this chunk's relocated symbols.
   llvm::iterator_range<symbol_iterator> symbols() const {
     return llvm::make_range(symbol_iterator(File, Relocs.begin()),

lld/COFF/InputFiles.cpp

@@ -132,17 +132,17 @@ void ObjectFile::initializeChunks() {
     if (!Config->Debug && Name.startswith(".debug"))
       continue;
 
-    // CodeView sections are stored to a different vector because they are
-    // not linked in the regular manner.
-    if (Name == ".debug" || Name.startswith(".debug$")) {
-      DebugChunks.push_back(make<SectionChunk>(this, Sec));
-      continue;
-    }
-
     if (Sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_REMOVE)
       continue;
     auto *C = make<SectionChunk>(this, Sec);
-    Chunks.push_back(C);
+
+    // CodeView sections are stored to a different vector because they are not
+    // linked in the regular manner.
+    if (C->isCodeView())
+      DebugChunks.push_back(C);
+    else
+      Chunks.push_back(C);
+
     SparseChunks[I] = C;
   }
 }

lld/COFF/PDB.cpp

@@ -164,10 +164,7 @@ static void addObjectsToPDB(BumpPtrAllocator &Alloc, SymbolTable *Symtab,
 
     // Now do all line info.
     for (SectionChunk *DebugChunk : File->getDebugChunks()) {
-      // FIXME: Debug chunks do not have a correct isLive() bit.
+      if (!DebugChunk->isLive() || DebugChunk->getSectionName() != ".debug$S")
-      // FIXME: When linker GC is off we need to ignore debug info whose
-      // associated symbol was discarded.
-      if (DebugChunk->getSectionName() != ".debug$S")
         continue;
 
       ArrayRef<uint8_t> RelocatedDebugContents =

lld/COFF/Writer.cpp

@@ -445,9 +445,12 @@ Optional<coff_symbol16> Writer::createSymbol(Defined *Def) {
   if (isa<DefinedRelative>(Def))
     return None;
 
-  if (auto *D = dyn_cast<DefinedRegular>(Def))
+  if (auto *D = dyn_cast<DefinedRegular>(Def)) {
-    if (!D->getChunk()->isLive())
+    // Don't write dead symbols or symbols in codeview sections to the symbol
+    // table.
+    if (!D->getChunk()->isLive() || D->getChunk()->isCodeView())
       return None;
+  }
 
   if (auto *Sym = dyn_cast<DefinedImportData>(Def))
     if (!Sym->File->Live)

lld/test/COFF/Inputs/pdb_comdat_bar.yaml

@@ -0,0 +1,440 @@
+--- !COFF
+header:          
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:        
+  - Name:            .drectve
+    Characteristics: [ IMAGE_SCN_LNK_INFO, IMAGE_SCN_LNK_REMOVE ]
+    Alignment:       1
+    SectionData:     2020202F44454641554C544C49423A224C4942434D5422202F44454641554C544C49423A224F4C444E414D45532220
+  - Name:            '.debug$S'
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
+    Alignment:       1
+    Subsections:     
+      - !Symbols
+        Records:         
+          - Kind:            S_OBJNAME
+            ObjNameSym:      
+              Signature:       0
+              ObjectName:      'C:\src\llvm-project\build\pdb_comdat_bar.obj'
+          - Kind:            S_COMPILE3
+            Compile3Sym:     
+              Flags:           [ SecurityChecks, HotPatch ]
+              Machine:         X64
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+              FrontendMinor:   0
+              FrontendBuild:   24215
+              FrontendQFE:     1
+              BackendMajor:    19
+              BackendMinor:    0
+              BackendBuild:    24215
+              BackendQFE:      1
+              Version:         'Microsoft (R) Optimizing Compiler'
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+          - 'c:\src\llvm-project\build\foo.h'
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+        Type:            IMAGE_REL_AMD64_REL32
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+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
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+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+...

lld/test/COFF/Inputs/pdb_comdat_main.yaml

@@ -0,0 +1,446 @@
+--- !COFF
+header:          
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:        
+  - Name:            .drectve
+    Characteristics: [ IMAGE_SCN_LNK_INFO, IMAGE_SCN_LNK_REMOVE ]
+    Alignment:       1
+    SectionData:     2020202F44454641554C544C49423A224C4942434D5422202F44454641554C544C49423A224F4C444E414D45532220
+  - Name:            '.debug$S'
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
+    Alignment:       1
+    Subsections:     
+      - !Symbols
+        Records:         
+          - Kind:            S_OBJNAME
+            ObjNameSym:      
+              Signature:       0
+              ObjectName:      'C:\src\llvm-project\build\pdb_comdat_main.obj'
+          - Kind:            S_COMPILE3
+            Compile3Sym:     
+              Flags:           [ SecurityChecks, HotPatch ]
+              Machine:         X64
+              FrontendMajor:   19
+              FrontendMinor:   0
+              FrontendBuild:   24215
+              FrontendQFE:     1
+              BackendMajor:    19
+              BackendMinor:    0
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lld/test/COFF/pdb-comdat.test

@@ -0,0 +1,52 @@
+Consider this example program with an inline function "foo":
+
+==> foo.h <==
+extern int global;
+__inline void foo() {
+  ++global;
+}
+void bar();
+==> pdb_comdat_main.c <==
+#include "foo.h"
+int main(void) {
+  foo();
+  bar();
+  return 42;
+}
+==> pdb_comdat_bar.c <==
+#include "foo.h"
+void bar(void) {
+  foo();
+}
+
+Both object files will contain debug info for foo, but only the debug info from
+pdb_comdat_main.obj should be included in the PDB.
+
+RUN: rm -rf %t && mkdir -p %t && cd %t
+RUN: yaml2obj %S/Inputs/pdb_comdat_main.yaml -o pdb_comdat_main.obj
+RUN: yaml2obj %S/Inputs/pdb_comdat_bar.yaml -o pdb_comdat_bar.obj
+RUN: lld-link pdb_comdat_main.obj pdb_comdat_bar.obj -out:t.exe -debug -pdb:t.pdb -nodefaultlib -entry:main
+RUN: llvm-pdbutil raw -l t.pdb | FileCheck %s
+
+CHECK:                            Lines
+CHECK: ============================================================
+CHECK-LABEL:   Mod 0000 | `{{.*}}pdb_comdat_main.obj`:
+CHECK:       c:\src\llvm-project\build\pdb_comdat_main.c (MD5: F969E51BBE373436D81492EB61387F36)
+CHECK:       c:\src\llvm-project\build\foo.h (MD5: D74D834EFAC3AE2B45E606A8320B1D5C)
+CHECK-LABEL:   Mod 0001 | `{{.*}}pdb_comdat_bar.obj`:
+CHECK:       c:\src\llvm-project\build\pdb_comdat_bar.c (MD5: 365279DB4FCBEDD721BBFC3B14A953C2)
+CHECK-NOT:       c:\src\llvm-project\build\foo.h
+CHECK-LABEL:   Mod 0002 | `* Linker *`:
+
+Reorder the object files and verify that the other table is selected.
+
+RUN: lld-link pdb_comdat_bar.obj pdb_comdat_main.obj -out:t.exe -debug -pdb:t.pdb -nodefaultlib -entry:main
+RUN: llvm-pdbutil raw -l t.pdb | FileCheck %s --check-prefix=REORDER
+
+REORDER-LABEL:   Mod 0000 | `{{.*}}pdb_comdat_bar.obj`:
+REORDER:       c:\src\llvm-project\build\pdb_comdat_bar.c (MD5: 365279DB4FCBEDD721BBFC3B14A953C2)
+REORDER:       c:\src\llvm-project\build\foo.h (MD5: D74D834EFAC3AE2B45E606A8320B1D5C)
+REORDER-LABEL:   Mod 0001 | `{{.*}}pdb_comdat_main.obj`:
+REORDER:       c:\src\llvm-project\build\pdb_comdat_main.c
+REORDER-NOT:       c:\src\llvm-project\build\foo.h
+REORDER-LABEL:   Mod 0002 | `* Linker *`: