Fix a bug that prevented setting a DebugLoc if the first SILInstruction

in the function is setup code for a closure and re-enable the assertions
that caught this on the bots.

rdar://problem/26955467

Author: adrian-prantl

lib/IRGen/IRBuilder.h

@@ -262,6 +262,7 @@ class IRBuilder : public IRBuilderBase {
   llvm::CallInst *CreateCall(llvm::Value *Callee, ArrayRef<llvm::Value *> Args,
                              const Twine &Name = "",
                              llvm::MDNode *FPMathTag = nullptr) {
+    assert((!DebugInfo || getCurrentDebugLocation()) && "no debugloc on call");
     auto Call = IRBuilderBase::CreateCall(Callee, Args, Name, FPMathTag);
     setCallingConvUsingCallee(Call);
     return Call;
@@ -271,6 +272,7 @@ class IRBuilder : public IRBuilderBase {
                              ArrayRef<llvm::Value *> Args,
                              const Twine &Name = "",
                              llvm::MDNode *FPMathTag = nullptr) {
+    assert((!DebugInfo || getCurrentDebugLocation()) && "no debugloc on call");
     auto Call = IRBuilderBase::CreateCall(FTy, Callee, Args, Name, FPMathTag);
     setCallingConvUsingCallee(Call);
     return Call;
@@ -280,6 +282,7 @@ class IRBuilder : public IRBuilderBase {
                              ArrayRef<llvm::Value *> Args,
                              const Twine &Name = "",
                              llvm::MDNode *FPMathTag = nullptr) {
+    assert((!DebugInfo || getCurrentDebugLocation()) && "no debugloc on call");
     auto Call = IRBuilderBase::CreateCall(Callee, Args, Name, FPMathTag);
     setCallingConvUsingCallee(Call);
     return Call;

lib/IRGen/IRGenDebugInfo.cpp

@@ -313,8 +313,9 @@ void IRGenDebugInfo::setCurrentLoc(IRBuilder &Builder, const SILDebugScope *DS,
   //
   // The actual closure has a closure expression as scope.
   if (Loc && isAbstractClosure(*Loc) && DS && !isAbstractClosure(DS->Loc)
-      && !Loc->is<ImplicitReturnLocation>())
-    return;
+      && !Loc->is<ImplicitReturnLocation>()) {
+    L.Line = L.Column = 0;
+  }
 
   if (L.Line == 0 && DS == LastScope) {
     // Reuse the last source location if we are still in the same