[NFC][DebugInfo] Factor out CodeView code into its own function

CodeView has its own needs / limitations for representing line 0.
However, this is adding control flow complexities that make changing the
underlying logic complicated for both cases. Furthermore, the
limitations above may be temporary if we change LLVM's backend; by
having a separate function, we can, in the future, easily unify the code
paths in the future by deleting the function.

(cherry picked from commit 9758099)

Author: felipepiovezan

lib/IRGen/IRGenDebugInfo.cpp

@@ -347,6 +347,12 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
   /// Convert a SILLocation into the corresponding LLVM Loc.
   FileAndLocation computeLLVMLoc(const SILDebugScope *DS, SILLocation Loc);
 
+  /// Compute the LLVM DebugLoc when targeting CodeView. In CodeView, zero is
+  /// not an artificial line location; attempt to avoid those line locations near
+  /// user code to reduce the number of breaks in the linetables.
+  FileAndLocation computeLLVMLocCodeView(const SILDebugScope *DS,
+                                         SILLocation Loc);
+
   static StringRef getFilenameFromDC(const DeclContext *DC) {
     if (auto *LF = dyn_cast<LoadedFile>(DC))
       return LF->getFilename();
@@ -2617,11 +2623,21 @@ bool IRGenDebugInfoImpl::lineEntryIsSane(FileAndLocation DL,
 }
 #endif
 
+IRGenDebugInfoImpl::FileAndLocation
+IRGenDebugInfoImpl::computeLLVMLocCodeView(const SILDebugScope *DS,
+                                           SILLocation Loc) {
+  // If the scope has not changed and the line number is either zero or
+  // artificial, we want to keep the most recent debug location.
+  if (DS == LastScope &&
+      (Loc.is<ArtificialUnreachableLocation>() || Loc.isLineZero(SM)))
+    return LastFileAndLocation;
+
+  // Decode the location.
+  return decodeFileAndLocation(Loc);
+}
+
 IRGenDebugInfoImpl::FileAndLocation
 IRGenDebugInfoImpl::computeLLVMLoc(const SILDebugScope *DS, SILLocation Loc) {
-  // NOTE: In CodeView, zero is not an artificial line location. We try to
-  //       avoid those line locations near user code to reduce the number
-  //       of breaks in the linetables.
   SILFunction *Fn = DS->getInlinedFunction();
   if (Fn && (Fn->isThunk() || Fn->isTransparent()))
     return {0, 0, CompilerGeneratedFile};
@@ -2631,24 +2647,14 @@ IRGenDebugInfoImpl::computeLLVMLoc(const SILDebugScope *DS, SILLocation Loc) {
   if (DS == LastScope && Loc.isHiddenFromDebugInfo())
     return LastFileAndLocation;
 
-  // If the scope has not changed and the line number is either zero or
-  // artificial, we want to keep the most recent debug location.
-  if (DS == LastScope &&
-      (Loc.is<ArtificialUnreachableLocation>() || Loc.isLineZero(SM)) &&
-      Opts.DebugInfoFormat == IRGenDebugInfoFormat::CodeView)
-    return LastFileAndLocation;
+  if (Opts.DebugInfoFormat == IRGenDebugInfoFormat::CodeView)
+    return computeLLVMLocCodeView(DS, Loc);
 
-  FileAndLocation L;
-  // Decode the location.
-  if (!Loc.isInPrologue() ||
-      Opts.DebugInfoFormat == IRGenDebugInfoFormat::CodeView)
-    L = decodeFileAndLocation(Loc);
-
-  // Otherwise use a line 0 artificial location, but the file from the
-  // location. If we are emitting CodeView, we do not want to use line zero
-  // since it does not represent an artificial line location.
-  if (Loc.isHiddenFromDebugInfo() &&
-      Opts.DebugInfoFormat != IRGenDebugInfoFormat::CodeView) {
+  FileAndLocation L =
+      Loc.isInPrologue() ? FileAndLocation() : decodeFileAndLocation(Loc);
+
+  // Otherwise use a line 0 artificial location, but the file from the location.
+  if (Loc.isHiddenFromDebugInfo()) {
     L.Line = 0;
     L.Column = 0;
   }