CodeGen: Fix CodeView crashes with empty llvm.dbg.cu

Author: arsenm

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

@@ -625,10 +625,13 @@ void CodeViewDebug::beginModule(Module *M) {
   if (Asm->hasDebugInfo()) {
     Node = *M->debug_compile_units_begin();
   } else {
+    auto DebugCompileUnits = MMI->getModule()->debug_compile_units();
+    if (DebugCompileUnits.empty())
+      return;
+
     // When emitting only compiler information, we may have only NoDebug CUs,
     // which would be skipped by debug_compile_units_begin.
-    NamedMDNode *CUs = MMI->getModule()->getNamedMetadata("llvm.dbg.cu");
-    Node = *CUs->operands().begin();
+    Node = *DebugCompileUnits.begin();
   }
   const auto *CU = cast<DICompileUnit>(Node);
   DISourceLanguageName Lang = CU->getSourceLanguage();
@@ -900,8 +903,11 @@ void CodeViewDebug::emitCompilerInformation() {
   OS.AddComment("CPUType");
   OS.emitInt16(static_cast<uint64_t>(TheCPU));
 
-  NamedMDNode *CUs = MMI->getModule()->getNamedMetadata("llvm.dbg.cu");
-  const MDNode *Node = *CUs->operands().begin();
+  auto CUs = MMI->getModule()->debug_compile_units();
+  if (CUs.empty())
+    return;
+
+  const MDNode *Node = *CUs.begin();
   const auto *CU = cast<DICompileUnit>(Node);
 
   StringRef CompilerVersion = CU->getProducer();
@@ -948,8 +954,11 @@ void CodeViewDebug::emitBuildInfo() {
   // not clear if the compiler path should refer to the executable for the
   // frontend or the backend. Leave it blank for now.
   TypeIndex BuildInfoArgs[BuildInfoRecord::MaxArgs] = {};
-  NamedMDNode *CUs = MMI->getModule()->getNamedMetadata("llvm.dbg.cu");
-  const MDNode *Node = *CUs->operands().begin(); // FIXME: Multiple CUs.
+  auto CUs = MMI->getModule()->debug_compile_units();
+  if (CUs.empty())
+    return;
+
+  const MDNode *Node = *CUs.begin(); // FIXME: Multiple CUs.
   const auto *CU = cast<DICompileUnit>(Node);
   const DIFile *MainSourceFile = CU->getFile();
   BuildInfoArgs[BuildInfoRecord::CurrentDirectory] =

llvm/test/DebugInfo/X86/codeview-empty-dbg-cu-crash.ll

@@ -0,0 +1,30 @@
+; RUN: llc -mtriple=x86_64-pc-windows-msvc < %s | FileCheck %s
+
+; CHECK: .file	"<stdin>"
+; CHECK-NEXT: .section	.debug$S,"dr"
+; CHECK-NEXT: .p2align	2, 0x0
+; CHECK-NEXT: .long	4                               # Debug section magic
+; CHECK-NEXT: .long	241
+; CHECK-NEXT: .long	.Ltmp1-.Ltmp0                   # Subsection size
+; CHECK-NEXT: .Ltmp0:
+; CHECK-NEXT: .short	.Ltmp3-.Ltmp2                   # Record length
+; CHECK-NEXT: .Ltmp2:
+; CHECK-NEXT: .short	4353                            # Record kind: S_OBJNAME
+; CHECK-NEXT: .long	0                               # Signature
+; CHECK-NEXT: .byte	0                               # Object name
+; CHECK-NEXT: .p2align	2, 0x0
+; CHECK-NEXT: .Ltmp3:
+; CHECK-NEXT: .short	.Ltmp5-.Ltmp4                   # Record length
+; CHECK-NEXT: .Ltmp4:
+; CHECK-NEXT: .short	4412                            # Record kind: S_COMPILE3
+; CHECK-NEXT: .long	3                               # Flags and language
+; CHECK-NEXT: .short	208                             # CPUType
+; CHECK-NEXT: .Ltmp1:
+; CHECK-NEXT: .p2align	2, 0x0
+; CHECK-NEXT: .cv_filechecksums                       # File index to string table offset subsection
+; CHECK-NEXT: .cv_stringtable                         # String table
+
+!llvm.dbg.cu = !{}
+!llvm.module.flags = !{!0}
+
+!0 = !{i32 2, !"Debug Info Version", i32 3}