LargeTypesReg2Mem: Fix copy_addr optimization

Make sure that the value we store is the loaded value ...
rdar://123340151

Author: aschwaighofer

lib/IRGen/LoadableByAddress.cpp

@@ -3306,7 +3306,7 @@ bool Peepholes::optimizeLoad(SILBasicBlock &BB, SILInstruction *I) {
     if (next2It == BB.end())
       return false;
     auto *store = dyn_cast<StoreInst>(&*next2It);
-    if (!store)
+    if (!store || store->getSrc() != LI)
       return false;
     if (ignore(store))
       return false;

test/IRGen/loadable_by_address_reg2mem.sil

@@ -29,6 +29,16 @@ struct Y {
   var y2: X
 }
 
+class C1 {
+}
+
+sil_vtable C1 {
+}
+
+struct Small {
+  var x1 : Int
+}
+
 // CHECK: sil @test1 : $@convention(thin) () -> () {
 // CHECK: bb0:
 // CHECK:   %0 = alloc_stack $Optional<X>
@@ -248,3 +258,14 @@ bb0:
   %t = tuple ()
   return %t : $()
 }
+
+sil @test10 : $@convention(thin) (@in_guaranteed C1, @in Small) -> () {
+bb0(%0 : $*C1, %1 : $*Small):
+  %2 = load %1 : $*Small
+  %3 = load %0 : $*C1
+  retain_value %3 : $C1
+  store %2 to %1 : $*Small
+  retain_value %3 : $C1
+  %t = tuple ()
+  return %t : $()
+}