CodeGen: Fix missing debug loc due to alloca

Builder save/restores insertion pointer when emitting addr space cast
for alloca, but does not save/restore debug loc, which causes verifier
failure for certain call instructions.

This patch fixes that.

Differential Revision: https://reviews.llvm.org/D39069

llvm-svn: 316484
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 2eb6d0a..6837377 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -74,12 +74,11 @@
   // cast alloca to the default address space when necessary.
   if (CastToDefaultAddrSpace && getASTAllocaAddressSpace() != LangAS::Default) {
     auto DestAddrSpace = getContext().getTargetAddressSpace(LangAS::Default);
-    auto CurIP = Builder.saveIP();
+    llvm::IRBuilderBase::InsertPointGuard IPG(Builder);
     Builder.SetInsertPoint(AllocaInsertPt);
     V = getTargetHooks().performAddrSpaceCast(
         *this, V, getASTAllocaAddressSpace(), LangAS::Default,
         Ty->getPointerTo(DestAddrSpace), /*non-null*/ true);
-    Builder.restoreIP(CurIP);
   }
 
   return Address(V, Align);