[AddressLowering] Handle store_borrow.

Thanks to the invariants of store_borrow, rewriting a store_borrow is a
simple matter of replacing its (non end_borrow) uses with uses of the
underlying address-only value whose use was stored.

Author: nate-chandler

lib/SILOptimizer/Mandatory/AddressLowering.cpp

@@ -3101,6 +3101,18 @@ class UseRewriter : SILInstructionVisitor<UseRewriter> {
     llvm::report_fatal_error("Unimplemented SelectValue use.");
   }
 
+  void visitStoreBorrowInst(StoreBorrowInst *sbi) {
+    auto addr = addrMat.materializeAddress(use->get());
+    SmallVector<Operand *, 4> uses(sbi->getUses());
+    for (auto *use : uses) {
+      if (auto *ebi = dyn_cast<EndBorrowInst>(use->getUser())) {
+        pass.deleter.forceDelete(ebi);
+      }
+    }
+    sbi->replaceAllUsesWith(addr);
+    pass.deleter.forceDelete(sbi);
+  }
+
   void rewriteStore(SILValue srcVal, SILValue destAddr,
                     IsInitialization_t isInit);
 

test/SILOptimizer/address_lowering.sil

@@ -2149,6 +2149,36 @@ bb0:
   return %retval : $()
 }
 
+// CHECK-LABEL: sil [ossa] @test_store_borrow_1_copy_addr : {{.*}} {
+// CHECK:         [[ADDR:%[^,]+]] = alloc_stack
+// CHECK:         apply undef<T>([[ADDR]])
+// CHECK:         [[COPY:%[^,]+]] = alloc_stack
+// CHECK:         copy_addr [[ADDR]] to [init] [[COPY]]
+// CHECK:         apply undef<T>([[COPY]])
+// CHECK:         destroy_addr [[COPY]]
+// CHECK:         dealloc_stack [[COPY]]
+// CHECK-NOT:     end_borrow [[ADDR]]
+// CHECK:         destroy_addr [[ADDR]]
+// CHECK-LABEL: } // end sil function 'test_store_borrow_1_copy_addr'
+sil [ossa] @test_store_borrow_1_copy_addr : $@convention(thin) <T> () -> () {
+entry:
+  %addr = alloc_stack $T
+  %instance = apply undef<T>() : $@convention(thin) <τ> () -> (@out τ)
+  %lifetime = begin_borrow %instance : $T
+  %borrow = store_borrow %lifetime to %addr : $*T
+  %copy = alloc_stack $T
+  copy_addr %borrow to [init] %copy : $*T
+  apply undef<T>(%copy) : $@convention(thin) <τ> (@inout τ) -> ()
+  destroy_addr %copy : $*T
+  dealloc_stack %copy : $*T
+  end_borrow %borrow : $*T
+  end_borrow %lifetime : $T
+  dealloc_stack %addr : $*T
+  destroy_value %instance : $T
+  %retval = tuple ()
+  return %retval : $()
+}
+
 // CHECK-LABEL: sil hidden [ossa] @test_unchecked_bitwise_cast :
 // CHECK: bb0(%0 : $*U, %1 : $*T, %2 : $@thick U.Type):
 // CHECK:   [[STK:%.*]] = alloc_stack $T