[Debugify] applyDebugify - remove unnecessary defaults arg values and assert dereferencable values (#127186)

The applyDebugify helpers were providing default arguments despite all callers providing them, so strip them for clarity.

The Function variant was asserting that DebugInfoBeforePass was non-null before dereferencing so I've added an equivalent assert to the Method variant as well.

Fixes #97626

Author: RKSimon

llvm/lib/Transforms/Utils/Debugify.cpp

@@ -214,30 +214,27 @@ bool llvm::applyDebugifyMetadata(
   return true;
 }
 
-static bool
-applyDebugify(Function &F,
-              enum DebugifyMode Mode = DebugifyMode::SyntheticDebugInfo,
-              DebugInfoPerPass *DebugInfoBeforePass = nullptr,
-              StringRef NameOfWrappedPass = "") {
+static bool applyDebugify(Function &F, enum DebugifyMode Mode,
+                          DebugInfoPerPass *DebugInfoBeforePass,
+                          StringRef NameOfWrappedPass = "") {
   Module &M = *F.getParent();
   auto FuncIt = F.getIterator();
   if (Mode == DebugifyMode::SyntheticDebugInfo)
     return applyDebugifyMetadata(M, make_range(FuncIt, std::next(FuncIt)),
                                  "FunctionDebugify: ", /*ApplyToMF*/ nullptr);
-  assert(DebugInfoBeforePass);
+  assert(DebugInfoBeforePass && "Missing debug info metadata");
   return collectDebugInfoMetadata(M, M.functions(), *DebugInfoBeforePass,
                                   "FunctionDebugify (original debuginfo)",
                                   NameOfWrappedPass);
 }
 
-static bool
-applyDebugify(Module &M,
-              enum DebugifyMode Mode = DebugifyMode::SyntheticDebugInfo,
-              DebugInfoPerPass *DebugInfoBeforePass = nullptr,
-              StringRef NameOfWrappedPass = "") {
+static bool applyDebugify(Module &M, enum DebugifyMode Mode,
+                          DebugInfoPerPass *DebugInfoBeforePass,
+                          StringRef NameOfWrappedPass = "") {
   if (Mode == DebugifyMode::SyntheticDebugInfo)
     return applyDebugifyMetadata(M, M.functions(),
                                  "ModuleDebugify: ", /*ApplyToMF*/ nullptr);
+  assert(DebugInfoBeforePass && "Missing debug info metadata");
   return collectDebugInfoMetadata(M, M.functions(), *DebugInfoBeforePass,
                                   "ModuleDebugify (original debuginfo)",
                                   NameOfWrappedPass);