Allow materializer callback to devolve responsibility (#319)

Author: vchuravy

src/utils.jl

@@ -6,8 +6,14 @@ export clone_into!, clone
 
 type_mapper_callback(typ, type_mapper) =
     Base.unsafe_convert(API.LLVMTypeRef, type_mapper[](LLVMType(typ)))
-materializer_callback(val, materializer) =
-    Base.unsafe_convert(API.LLVMValueRef, materializer[](Value(val)))
+function materializer_callback(val, materializer)
+    new_val = materializer[](Value(val))
+    if new_val === nothing
+        return Base.unsafe_convert(API.LLVMValueRef, C_NULL)
+    else
+        return Base.unsafe_convert(API.LLVMValueRef, new_val)
+    end
+end
 
 function clone_into!(new::Function, old::Function;
                      value_map::Dict{Value,Value}=Dict{Value,Value}(),

test/utils.jl

@@ -14,9 +14,13 @@
         @dispose builder=Builder(ctx) begin
             entry = BasicBlock(f, "entry"; ctx)
             position!(builder, entry)
-
+            ptr = const_inttoptr(
+                ConstantInt(0xdeadbeef%UInt; ctx),
+                LLVM.PointerType(LLVM.Int32Type(ctx)))
             tmp = add!(builder, parameters(f)[1], parameters(f)[2], "tmp")
-            ret!(builder, tmp)
+            tmp2 = load!(builder, ptr)
+            tmp3 = add!(builder, tmp, tmp2)
+            ret!(builder, tmp3)
 
             verify(mod)
         end
@@ -70,8 +74,12 @@
                 end
             end
             function materializer(val)
+                if val isa Union{LLVM.ConstantExpr, ConstantInt}
+                    # test that we can return nothing
+                    return nothing
+                end
                 # not needed here
-                error()
+                error("")
             end
             clone_into!(new_f, f; value_map, type_mapper, materializer)