[Mem2Reg] Only lifetime canonicalize in OSSA.

Bail both on collecting stores and canonicalizing values if the function
being optimized doesn't have ownership.

Author: nate-chandler

lib/SILOptimizer/Transforms/SILMem2Reg.cpp

@@ -2153,6 +2153,8 @@ void MemoryToRegisters::removeSingleBlockAllocation(AllocStackInst *asi) {
 void MemoryToRegisters::collectStoredValues(AllocStackInst *asi,
                                             StackList<SILValue> &owned,
                                             StackList<SILValue> &guaranteed) {
+  if (!f.hasOwnership())
+    return;
   for (auto *use : asi->getUses()) {
     auto *user = use->getUser();
     if (auto *si = dyn_cast<StoreInst>(user)) {
@@ -2166,6 +2168,8 @@ void MemoryToRegisters::collectStoredValues(AllocStackInst *asi,
 void MemoryToRegisters::canonicalizeValueLifetimes(
     StackList<SILValue> &owned, StackList<SILValue> &guaranteed,
     BasicBlockSetVector &livePhiBlocks) {
+  if (!f.hasOwnership())
+    return;
   if (Mem2RegDisableLifetimeCanonicalization)
     return;
 

test/SILOptimizer/mem2reg.sil

@@ -518,3 +518,16 @@ sil @load_from_uninitialized_empty : $@convention(thin) () -> (Pair<Pair<EmptySt
   dealloc_stack %addr : $*(Pair<Pair<EmptyStruct, EmptyStruct>, EmptyStruct>, (EmptyStruct, EmptyStruct), EmptyStruct)
   return %value : $(Pair<Pair<EmptyStruct, EmptyStruct>, EmptyStruct>, (EmptyStruct, EmptyStruct), EmptyStruct)
 }
+
+
+// CHECK-LABEL: sil @dont_canonicalize_undef : {{.*}} {
+// CHECK:         [[RETVAL:%[^,]+]] = tuple
+// CHECK:         return [[RETVAL]]
+// CHECK-LABEL: } // end sil function 'dont_canonicalize_undef'
+sil @dont_canonicalize_undef : $@convention(thin) () -> () {
+  %addr = alloc_stack $()
+  store undef to %addr : $*()
+  dealloc_stack %addr : $*()
+  %retval = tuple ()
+  return %retval : $()
+}