[clang] [llvm] [CodeGen][COFF] Always emit CodeView compiler info on Windows targets (PR #142970)

[Daniel Paoliello via llvm-commits]

================
@@ -613,19 +613,30 @@ static SourceLanguage MapDWLangToCVLang(unsigned DWLang) {
 void CodeViewDebug::beginModule(Module *M) {
   // If module doesn't have named metadata anchors or COFF debug section
   // is not available, skip any debug info related stuff.
-  if (!Asm->hasDebugInfo() ||
-      !Asm->getObjFileLowering().getCOFFDebugSymbolsSection()) {
+  if (!Asm->getObjFileLowering().getCOFFDebugSymbolsSection()) {
     Asm = nullptr;
     return;
   }
 
   TheCPU = mapArchToCVCPUType(M->getTargetTriple().getArch());
 
   // Get the current source language.
-  const MDNode *Node = *M->debug_compile_units_begin();
+  const MDNode *Node;
+  if (Asm->hasDebugInfo()) {
+    Node = *M->debug_compile_units_begin();
+  } else {
+    // 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();
+  }
   const auto *CU = cast<DICompileUnit>(Node);
 
   CurrentSourceLanguage = MapDWLangToCVLang(CU->getSourceLanguage());
+  NoDebug =
----------------
dpaoliello wrote:

Would it be possible to lift this and the early return into the `else` above? Or is there a case where `hasDebugInfo` is true, but we have NoDebug CUs?

https://github.com/llvm/llvm-project/pull/142970