DwarfDebug: Avoid creating new DebugLocs in the backend

Don't use `DebugLoc::getFnDebugLoc()`, which creates new `MDLocation`s,
in the backend.  We just want to grab the subprogram here anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233601 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/DebugInfoMetadata.h

@@ -889,6 +889,12 @@ protected:
   ~MDLocalScope() {}
 
 public:
+  /// \brief Get the subprogram for this scope.
+  ///
+  /// Return this if it's an \a MDSubprogram; otherwise, look up the scope
+  /// chain.
+  MDSubprogram *getSubprogram() const;
+
   static bool classof(const Metadata *MD) {
     return MD->getMetadataID() == MDSubprogramKind ||
            MD->getMetadataID() == MDLexicalBlockKind ||

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -1168,13 +1168,11 @@ void DwarfDebug::beginFunction(const MachineFunction *MF) {
 
   // Record beginning of function.
   PrologEndLoc = findPrologueEndLoc(MF);
-  if (PrologEndLoc) {
-    DebugLoc FnStartDL = PrologEndLoc.getFnDebugLoc();
-
+  if (MDLocation *L = PrologEndLoc) {
     // We'd like to list the prologue as "not statements" but GDB behaves
     // poorly if we do that. Revisit this with caution/GDB (7.5+) testing.
-    recordSourceLine(FnStartDL.getLine(), FnStartDL.getCol(),
-                     FnStartDL.getScope(), DWARF2_FLAG_IS_STMT);
+    auto *SP = L->getInlinedAtScope()->getSubprogram();
+    recordSourceLine(SP->getScopeLine(), 0, SP, DWARF2_FLAG_IS_STMT);
   }
 }
 

lib/IR/DebugInfoMetadata.cpp

@@ -238,6 +238,12 @@ MDCompileUnit *MDCompileUnit::getImpl(
       (SourceLanguage, IsOptimized, RuntimeVersion, EmissionKind), Ops);
 }
 
+MDSubprogram *MDLocalScope::getSubprogram() const {
+  if (auto *Block = dyn_cast<MDLexicalBlockBase>(this))
+    return Block->getScope()->getSubprogram();
+  return const_cast<MDSubprogram *>(cast<MDSubprogram>(this));
+}
+
 MDSubprogram *MDSubprogram::getImpl(
     LLVMContext &Context, Metadata *Scope, MDString *Name,
     MDString *LinkageName, Metadata *File, unsigned Line, Metadata *Type,