AliasAnalysis: look through begin_cow_mutation and end_cow_mutation when getting the root of a reference

Author: eeckstein

lib/SIL/Utils/InstructionUtils.cpp

@@ -81,6 +81,12 @@ SILValue swift::getUnderlyingObject(SILValue v) {
     v2 = stripAddressProjections(v2);
     v2 = stripIndexingInsts(v2);
     v2 = lookThroughOwnershipInsts(v2);
+    if (auto *ecm = dyn_cast<EndCOWMutationInst>(v2)) {
+      v2 = ecm->getOperand();
+    } else if (auto *mvr = dyn_cast<MultipleValueInstructionResult>(v2)) {
+      if (auto *bci = dyn_cast<BeginCOWMutationInst>(mvr->getParent()))
+        v2 = bci->getOperand();
+    }
     if (v2 == v)
       return v2;
     v = v2;

lib/SIL/Utils/Projection.cpp

@@ -380,6 +380,15 @@ llvm::Optional<ProjectionPath> ProjectionPath::getProjectionPath(SILValue Start,
 
   auto Iter = End;
   while (Start != Iter) {
+
+    if (auto *mvr = dyn_cast<MultipleValueInstructionResult>(Iter)) {
+      if (auto *bci = dyn_cast<BeginCOWMutationInst>(mvr->getParent())) {
+        Iter = bci->getOperand();
+        continue;
+      }
+      break;
+    }
+
     // end_cow_mutation and begin_access are not projections, but we need to be
     // able to form valid ProjectionPaths across them, otherwise optimization
     // passes like RLE/DSE cannot recognize their locations.

test/SILOptimizer/basic-aa.sil

@@ -628,3 +628,21 @@ bb0(%0 : $P):
   return %6 : $()
 }
 
+// CHECK-LABEL: @testCowMutation
+// CHECK:       PAIR #23.
+// CHECK-NEXT:    %4 = ref_tail_addr %0 : $X, $Int32
+// CHECK-NEXT:    %5 = ref_tail_addr %3 : $X, $Int32
+// CHECK-NEXT:  MustAlias
+sil @testCowMutation : $@convention(thin) () -> () {
+bb0:
+  %0 = alloc_ref $X
+  (%1, %2) = begin_cow_mutation %0 : $X
+  %3 = end_cow_mutation %2 : $X
+  %4 = ref_tail_addr %0 : $X, $Int32
+  %5 = ref_tail_addr %3 : $X, $Int32
+  fix_lifetime %4 : $*Int32
+  fix_lifetime %5 : $*Int32
+  %99 = tuple ()
+  return %99 : $()
+}
+