Fix a logic error that would cause shadow copies to be emitted at -O.

<rdar://problem/27206870>

Author: adrian-prantl

lib/IRGen/IRGenSIL.cpp

@@ -626,10 +626,12 @@ class IRGenSILFunction :
                               StringRef Name, unsigned ArgNo,
                               Alignment Align = Alignment(0)) {
     auto Ty = Storage->getType();
-    if (IGM.IRGen.Opts.Optimize || (ArgNo == 0) ||
+    if (IGM.IRGen.Opts.Optimize ||
         isa<llvm::AllocaInst>(Storage) ||
         isa<llvm::UndefValue>(Storage) ||
-        Ty == IGM.RefCountedPtrTy) { // No debug info is emitted for refcounts.
+        Ty == IGM.RefCountedPtrTy) // No debug info is emitted for refcounts.
+      return Storage;
+    if (ArgNo == 0) {
       // Account for bugs in LLVM.
       //
       // - The LLVM type legalizer currently doesn't update debug

test/DebugInfo/local-vars.swift.gyb

@@ -7,6 +7,10 @@
 // RUN: %target-swift-frontend %t.swift -g -c -o %t.o
 // RUN: llvm-dwarfdump --debug-dump=info %t.o \
 // RUN:   | FileCheck %t.swift --check-prefix=DWARF
+// RUN: %target-swift-frontend %t.swift -O -g -emit-ir -o - \
+// RUN:   | FileCheck %t.swift --check-prefix=OPTZNS
+
+// OPTZNS-NOT: alloca{{.*}}.addr
 
 public class C {
   let member : Int