Shadow copies: Use the function's debug scope for the artificial location

instead of the variable's potentially incorrectly not inlined scope.

rdar://problem/27206870

Author: adrian-prantl

lib/IRGen/IRGenSIL.cpp

@@ -656,7 +656,7 @@ class IRGenSILFunction :
     if (!Alloca.isValid())
       Alloca = createAlloca(Ty, Align, Name+".addr");
 
-    ArtificialLocation AutoRestore(Scope, IGM.DebugInfo, Builder);
+    ArtificialLocation AutoRestore(getDebugScope(), IGM.DebugInfo, Builder);
     Builder.CreateStore(Storage, Alloca.getAddress(), Align);
     return Alloca.getAddress();
   }

test/DebugInfo/guard-let.swift

@@ -8,7 +8,8 @@ public func f(_ i : Int?)
   // The shadow copy store should not have a location.
   // CHECK: store {{(i32|i64)}} %[[PHI]], {{(i32|i64)}}* %val.addr, align {{(4|8)}}, !dbg ![[DBG0:.*]]
   // CHECK: @llvm.dbg.declare(metadata {{(i32|i64)}}* %val.addr, {{.*}}, !dbg ![[DBG1:.*]]
-  // CHECK: ![[DBG0]] = !DILocation(line: 0,
+  // CHECK: ![[F:.*]] = distinct !DISubprogram(name: "f",
+  // CHECK: ![[DBG0]] = !DILocation(line: 0, scope: ![[F]])
   // CHECK: ![[DBG1]] = !DILocation(line: [[@LINE+1]],
   guard let val = i else { return }
   use(val)