Emit global variables as S_CONSTANT records for codeview debug info.

Summary:
This emits S_CONSTANT records for global variables.
Currently this emits records for the global variables already being tracked in the
LLVM IR metadata, which are just constant global variables; we'll also want S_CONSTANTs
for static data members and enums.

Related to https://bugs.llvm.org/show_bug.cgi?id=41615

Reviewers: rnk

Subscribers: aprantl, hiraditya, llvm-commits, thakis

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61926

llvm-svn: 360948

lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

@@ -41,6 +41,7 @@
 #include "llvm/Config/llvm-config.h"
 #include "llvm/DebugInfo/CodeView/CVTypeVisitor.h"
 #include "llvm/DebugInfo/CodeView/CodeView.h"
+#include "llvm/DebugInfo/CodeView/CodeViewRecordIO.h"
 #include "llvm/DebugInfo/CodeView/ContinuationRecordBuilder.h"
 #include "llvm/DebugInfo/CodeView/DebugInlineeLinesSubsection.h"
 #include "llvm/DebugInfo/CodeView/EnumTables.h"
@@ -66,6 +67,7 @@
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/BinaryByteStream.h"
 #include "llvm/Support/BinaryStreamReader.h"
+#include "llvm/Support/BinaryStreamWriter.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
@@ -2940,10 +2942,19 @@ void CodeViewDebug::collectGlobalVariableInfo() {
   for (const MDNode *Node : CUs->operands()) {
     const auto *CU = cast<DICompileUnit>(Node);
     for (const auto *GVE : CU->getGlobalVariables()) {
+      const DIGlobalVariable *DIGV = GVE->getVariable();
+      const DIExpression *DIE = GVE->getExpression();
+
+      // Emit constant global variables in a global symbol section.
+      if (GlobalMap.count(GVE) == 0 && DIE->isConstant()) {
+        CVGlobalVariable CVGV = {DIGV, DIE};
+        GlobalVariables.emplace_back(std::move(CVGV));
+      }
+
       const auto *GV = GlobalMap.lookup(GVE);
       if (!GV || GV->isDeclarationForLinker())
         continue;
-      const DIGlobalVariable *DIGV = GVE->getVariable();
+
       DIScope *Scope = DIGV->getScope();
       SmallVector<CVGlobalVariable, 1> *VariableList;
       if (Scope && isa<DILocalScope>(Scope)) {
@@ -2958,7 +2969,7 @@ void CodeViewDebug::collectGlobalVariableInfo() {
         // Emit this global variable into a COMDAT section.
         VariableList = &ComdatVariables;
       else
-        // Emit this globla variable in a single global symbol section.
+        // Emit this global variable in a single global symbol section.
         VariableList = &GlobalVariables;
       CVGlobalVariable CVGV = {DIGV, GV};
       VariableList->emplace_back(std::move(CVGV));
@@ -2981,13 +2992,14 @@ void CodeViewDebug::emitDebugInfoForGlobals() {
   // Second, emit each global that is in a comdat into its own .debug$S
   // section along with its own symbol substream.
   for (const CVGlobalVariable &CVGV : ComdatVariables) {
-    MCSymbol *GVSym = Asm->getSymbol(CVGV.GV);
+    const GlobalVariable *GV = CVGV.GVInfo.get<const GlobalVariable *>();
+    MCSymbol *GVSym = Asm->getSymbol(GV);
     OS.AddComment("Symbol subsection for " +
-            Twine(GlobalValue::dropLLVMManglingEscape(CVGV.GV->getName())));
+                  Twine(GlobalValue::dropLLVMManglingEscape(GV->getName())));
     switchToDebugSectionForSymbol(GVSym);
     MCSymbol *EndLabel = beginCVSubsection(DebugSubsectionKind::Symbols);
     // FIXME: emitDebugInfoForGlobal() doesn't handle DIExpressions.
-    emitDebugInfoForGlobal(CVGV.DIGV, CVGV.GV, GVSym);
+    emitDebugInfoForGlobal(CVGV);
     endCVSubsection(EndLabel);
   }
 }
@@ -3007,31 +3019,57 @@ void CodeViewDebug::emitDebugInfoForRetainedTypes() {
 // Emit each global variable in the specified array.
 void CodeViewDebug::emitGlobalVariableList(ArrayRef<CVGlobalVariable> Globals) {
   for (const CVGlobalVariable &CVGV : Globals) {
-    MCSymbol *GVSym = Asm->getSymbol(CVGV.GV);
     // FIXME: emitDebugInfoForGlobal() doesn't handle DIExpressions.
-    emitDebugInfoForGlobal(CVGV.DIGV, CVGV.GV, GVSym);
+    emitDebugInfoForGlobal(CVGV);
   }
 }
 
-void CodeViewDebug::emitDebugInfoForGlobal(const DIGlobalVariable *DIGV,
+void CodeViewDebug::emitDebugInfoForGlobal(const CVGlobalVariable &CVGV) {
-                                           const GlobalVariable *GV,
+  const DIGlobalVariable *DIGV = CVGV.DIGV;
-                                           MCSymbol *GVSym) {
+  if (const GlobalVariable *GV =
-  // DataSym record, see SymbolRecord.h for more info. Thread local data
+          CVGV.GVInfo.dyn_cast<const GlobalVariable *>()) {
-  // happens to have the same format as global data.
+    // DataSym record, see SymbolRecord.h for more info. Thread local data
-  SymbolKind DataSym = GV->isThreadLocal()
+    // happens to have the same format as global data.
-                           ? (DIGV->isLocalToUnit() ? SymbolKind::S_LTHREAD32
+    MCSymbol *GVSym = Asm->getSymbol(GV);
-                                                    : SymbolKind::S_GTHREAD32)
+    SymbolKind DataSym = GV->isThreadLocal()
-                           : (DIGV->isLocalToUnit() ? SymbolKind::S_LDATA32
+                             ? (DIGV->isLocalToUnit() ? SymbolKind::S_LTHREAD32
-                                                    : SymbolKind::S_GDATA32);
+                                                      : SymbolKind::S_GTHREAD32)
-  MCSymbol *DataEnd = beginSymbolRecord(DataSym);
+                             : (DIGV->isLocalToUnit() ? SymbolKind::S_LDATA32
-  OS.AddComment("Type");
+                                                      : SymbolKind::S_GDATA32);
-  OS.EmitIntValue(getCompleteTypeIndex(DIGV->getType()).getIndex(), 4);
+    MCSymbol *DataEnd = beginSymbolRecord(DataSym);
-  OS.AddComment("DataOffset");
+    OS.AddComment("Type");
-  OS.EmitCOFFSecRel32(GVSym, /*Offset=*/0);
+    OS.EmitIntValue(getCompleteTypeIndex(DIGV->getType()).getIndex(), 4);
-  OS.AddComment("Segment");
+    OS.AddComment("DataOffset");
-  OS.EmitCOFFSectionIndex(GVSym);
+    OS.EmitCOFFSecRel32(GVSym, /*Offset=*/0);
-  OS.AddComment("Name");
+    OS.AddComment("Segment");
-  const unsigned LengthOfDataRecord = 12;
+    OS.EmitCOFFSectionIndex(GVSym);
-  emitNullTerminatedSymbolName(OS, DIGV->getName(), LengthOfDataRecord);
+    OS.AddComment("Name");
-  endSymbolRecord(DataEnd);
+    const unsigned LengthOfDataRecord = 12;
+    emitNullTerminatedSymbolName(OS, DIGV->getName(), LengthOfDataRecord);
+    endSymbolRecord(DataEnd);
+  } else {
+    // FIXME: Currently this only emits the global variables in the IR metadata.
+    // This should also emit enums and static data members.
+    const DIExpression *DIE = CVGV.GVInfo.get<const DIExpression *>();
+    assert(DIE->isConstant() &&
+           "Global constant variables must contain a constant expression.");
+    uint64_t Val = DIE->getElement(1);
+
+    MCSymbol *SConstantEnd = beginSymbolRecord(SymbolKind::S_CONSTANT);
+    OS.AddComment("Type");
+    OS.EmitIntValue(getTypeIndex(DIGV->getType()).getIndex(), 4);
+    OS.AddComment("Value");
+
+    // Encoded integers shouldn't need more than 10 bytes.
+    uint8_t data[10];
+    BinaryStreamWriter Writer(data, llvm::support::endianness::little);
+    CodeViewRecordIO IO(Writer);
+    cantFail(IO.mapEncodedInteger(Val));
+    StringRef SRef((char *)data, Writer.getOffset());
+    OS.EmitBinaryData(SRef);
+
+    OS.AddComment("Name");
+    emitNullTerminatedSymbolName(OS, DIGV->getDisplayName());
+    endSymbolRecord(SConstantEnd);
+  }
 }

lib/CodeGen/AsmPrinter/CodeViewDebug.h

@@ -17,6 +17,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/MapVector.h"
+#include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/CodeGen/DbgEntityHistoryCalculator.h"
@@ -100,7 +101,7 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
 
   struct CVGlobalVariable {
     const DIGlobalVariable *DIGV;
-    const GlobalVariable *GV;
+    PointerUnion<const GlobalVariable *, const DIExpression *> GVInfo;
   };
 
   struct InlineSite {
@@ -313,8 +314,7 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
 
   void emitDebugInfoForGlobals();
   void emitGlobalVariableList(ArrayRef<CVGlobalVariable> Globals);
-  void emitDebugInfoForGlobal(const DIGlobalVariable *DIGV,
+  void emitDebugInfoForGlobal(const CVGlobalVariable &CVGV);
-                              const GlobalVariable *GV, MCSymbol *GVSym);
 
   /// Opens a subsection of the given kind in a .debug$S codeview section.
   /// Returns an end label for use with endCVSubsection when the subsection is

test/DebugInfo/COFF/global-constants.ll

@@ -0,0 +1,64 @@
+; RUN: llc < %s | FileCheck %s --check-prefix=ASM
+; RUN: llc < %s -filetype=obj | llvm-readobj - --codeview | FileCheck %s --check-prefix=OBJ
+
+; C++ source to regenerate:
+; const int Test1 = 1;
+; int main() {
+;   return Test1;
+; }
+; $ clang t.cpp -S -emit-llvm -g -gcodeview -o t.ll
+
+; ASM-LABEL:  .long 241              # Symbol subsection for globals
+
+; ASM:        .short {{.*-.*}}       # Record length
+; ASM:        .short 4359            # Record kind: S_CONSTANT
+; ASM-NEXT:   .long 4099             # Type
+; ASM-NEXT:   .byte 0x01, 0x00       # Value
+; ASM-NEXT:   .asciz "Test1"         # Name
+
+; OBJ:        CodeViewDebugInfo [
+; OBJ:          Section: .debug$S
+; OBJ:          Magic: 0x4
+; OBJ:          Subsection [
+; OBJ:            SubSectionType: Symbols (0xF1)
+; OBJ:            ConstantSym {
+; OBJ-NEXT:         Kind: S_CONSTANT (0x1107)
+; OBJ-NEXT:         Type: const int (0x1003)
+; OBJ-NEXT:         Value: 1
+; OBJ-NEXT:         Name: Test1
+; OBJ-NEXT:       }
+
+; ModuleID = 't.cpp'
+source_filename = "t.cpp"
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+; Function Attrs: noinline norecurse nounwind optnone
+define dso_local i32 @main() #0 !dbg !13 {
+entry:
+  %retval = alloca i32, align 4
+  store i32 0, i32* %retval, align 4
+  ret i32 1, !dbg !16
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!9, !10, !11}
+!llvm.ident = !{!12}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 9.0.0 (https://github.com/llvm/llvm-project.git 4a1902b6739e3087a03c0ac7ab85b640764e9335)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3, nameTableKind: None)
+!1 = !DIFile(filename: "<stdin>", directory: "C:\5Csrc\5Ctest", checksumkind: CSK_MD5, checksum: "0d5ef00bdd80bdb409a3deac9938f20d")
+!2 = !{}
+!3 = !{!4}
+!4 = !DIGlobalVariableExpression(var: !5, expr: !DIExpression(DW_OP_constu, 1, DW_OP_stack_value))
+!5 = distinct !DIGlobalVariable(name: "Test1", scope: !0, file: !6, line: 1, type: !7, isLocal: true, isDefinition: true)
+!6 = !DIFile(filename: "t.cpp", directory: "C:\5Csrc\5Ctest", checksumkind: CSK_MD5, checksum: "0d5ef00bdd80bdb409a3deac9938f20d")
+!7 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !8)
+!8 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!9 = !{i32 2, !"CodeView", i32 1}
+!10 = !{i32 2, !"Debug Info Version", i32 3}
+!11 = !{i32 1, !"wchar_size", i32 2}
+!12 = !{!"clang version 9.0.0 (https://github.com/llvm/llvm-project.git 4a1902b6739e3087a03c0ac7ab85b640764e9335)"}
+!13 = distinct !DISubprogram(name: "main", scope: !6, file: !6, line: 3, type: !14, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!14 = !DISubroutineType(types: !15)
+!15 = !{!8}
+!16 = !DILocation(line: 4, scope: !13)