Add support for open_existential_box_value in Address Lowering

Author: meg-gupta

lib/SILOptimizer/Mandatory/AddressLowering.cpp

@@ -37,7 +37,7 @@
 ///
 /// 1. Reused-storage: Some operations are guaranteed to reuse their operand's
 /// storage. This includes extracting an enum payload and opening an existential
-/// value. This is required avoid introducing new copies or moves.
+/// value. This is required to avoid introducing new copies or moves.
 ///
 ///   // %data's storage must reuse storage allocated for %enum
 ///   %data = unchecked_enum_data %enum : $Optional<T>, #Optional.some!enumelt
@@ -2503,12 +2503,6 @@ class UseRewriter : SILInstructionVisitor<UseRewriter> {
   // types.
   void visitOpenExistentialValueInst(OpenExistentialValueInst *openExistential);
 
-  void visitOpenExistentialBoxValueInst(
-      OpenExistentialBoxValueInst *openExistentialBox) {
-    // FIXME: Unimplemented
-    llvm::report_fatal_error("Unimplemented OpenExistentialBox use.");
-  }
-
   void visitReturnInst(ReturnInst *returnInst) {
     // Returns are rewritten for any function with indirect results after
     // opaque value rewriting.
@@ -2931,11 +2925,18 @@ class DefRewriter : SILInstructionVisitor<DefRewriter> {
     addrMat.initializeComposingUse(&initExistentialValue->getOperandRef());
   }
 
-  // Project an opaque value out of a box-type existential.
   void visitOpenExistentialBoxValueInst(
-      OpenExistentialBoxValueInst *openExistentialBox) {
-    // FIXME: Unimplemented
-    llvm::report_fatal_error("Unimplemented OpenExistentialBoxValue def.");
+      OpenExistentialBoxValueInst *openExistentialBoxValue) {
+    // Replace the module's openedArchetypesDef
+    pass.getModule()->willDeleteInstruction(openExistentialBoxValue);
+
+    auto *openAddr = builder.createOpenExistentialBox(
+        openExistentialBoxValue->getLoc(),
+        openExistentialBoxValue->getOperand(),
+        openExistentialBoxValue->getType().getAddressType());
+
+    openExistentialBoxValue->replaceAllTypeDependentUsesWith(openAddr);
+    markRewritten(openExistentialBoxValue, openAddr);
   }
 
   // Load an opaque value.
@@ -2970,6 +2971,14 @@ class DefRewriter : SILInstructionVisitor<DefRewriter> {
     for (Operand &operand : tupleInst->getAllOperands())
       addrMat.initializeComposingUse(&operand);
   }
+
+  void markRewritten(SILValue oldValue, SILValue addr) {
+    auto &storage = pass.valueStorageMap.getStorage(oldValue);
+    // getReusedStorageOperand() ensures that oldValue does not already have
+    // separate storage. So there's no need to delete its alloc_stack.
+    assert(!storage.storageAddress || storage.storageAddress == addr);
+    storage.storageAddress = addr;
+  }
 };
 } // end anonymous namespace
 
@@ -3124,7 +3133,8 @@ static void deleteRewrittenInstructions(AddressLoweringState &pass) {
       }
     }
     LLVM_DEBUG(llvm::dbgs() << "DEAD "; deadInst->dump());
-    if (!isa<OpenExistentialValueInst>(deadInst)) {
+    if (!isa<OpenExistentialValueInst>(deadInst) &&
+        !isa<OpenExistentialBoxValueInst>(deadInst)) {
       pass.deleter.forceDeleteWithUsers(deadInst);
       continue;
     }