handle scope correctly for @isdefined

this allows testing whether a variable is defined,
and may be especially useful for emitting from a macro
(which may want to conditionally initialize a variable)

Author: vtjnash

NEWS.md

@@ -4,6 +4,9 @@ Julia v0.7.0 Release Notes
 New language features
 ---------------------
 
+  * Local variables can be tested for being defined
+    using the new `@isdefined variable` macro ([#TBD]).
+
 Language changes
 ----------------
 

base/inference.jl

@@ -542,7 +542,7 @@ add_tfunc(===, 2, 2,
         end
         return Bool
     end)
-add_tfunc(isdefined, 1, IInf, (args...)->Bool)
+add_tfunc(isdefined, 1, 2, (args...)->Bool)
 add_tfunc(Core.sizeof, 1, 1, x->Int)
 add_tfunc(nfields, 1, 1,
     function (x::ANY)
@@ -2064,6 +2064,8 @@ function abstract_eval(e::ANY, vtypes::VarTable, sv::InferenceState)
         return abstract_eval_constant(e.args[1])
     elseif e.head === :invoke
         error("type inference data-flow error: tried to double infer a function")
+    elseif e.head === :isdefined
+        return Bool
     else
         t = Any
     end

base/reflection.jl

@@ -171,10 +171,10 @@ isconst(m::Module, s::Symbol) =
 """
     @isdefined s -> Bool
 
-Tests whether symbol `s` is defined in the current scope.
+Tests whether variable `s` is defined in the current scope.
 """
 macro isdefined(s::Symbol)
-    return :(isdefined($__module__, $(QuoteNode(s))))
+    return Expr(:isdefined, esc(s))
 end
 
 # return an integer such that object_id(x)==object_id(y) if x===y

src/ast.c

@@ -56,6 +56,7 @@ jl_sym_t *inert_sym; jl_sym_t *vararg_sym;
 jl_sym_t *unused_sym; jl_sym_t *static_parameter_sym;
 jl_sym_t *polly_sym; jl_sym_t *inline_sym;
 jl_sym_t *propagate_inbounds_sym;
+jl_sym_t *isdefined_sym;
 
 static uint8_t flisp_system_image[] = {
 #include <julia_flisp.boot.inc>
@@ -431,6 +432,7 @@ void jl_init_frontend(void)
     polly_sym = jl_symbol("polly");
     inline_sym = jl_symbol("inline");
     propagate_inbounds_sym = jl_symbol("propagate_inbounds");
+    isdefined_sym = jl_symbol("isdefined");
 }
 
 JL_DLLEXPORT void jl_lisp_prompt(void)

src/ccall.cpp

@@ -95,7 +95,7 @@ static bool runtime_sym_gvs(const char *f_lib, const char *f_name, MT &&M,
         }
     }
     if (libsym == NULL) {
-        libsym = *(void**)jl_get_global(libptrgv);
+        libsym = *(void**)jl_get_globalvar(libptrgv);
     }
     assert(libsym != NULL);
 

src/codegen.cpp

@@ -357,6 +357,7 @@ static Function *jlboundserrorv_func;
 static Function *jlcheckassign_func;
 static Function *jldeclareconst_func;
 static Function *jlgetbindingorerror_func;
+static Function *jlboundp_func;
 static Function *jltopeval_func;
 static Function *jlcopyast_func;
 static Function *jltuple_func;
@@ -2325,7 +2326,6 @@ static void simple_escape_analysis(jl_value_t *expr, bool esc, jl_codectx_t *ctx
             }
         }
         else if (e->head == foreigncall_sym) {
-            esc = true;
             simple_escape_analysis(jl_exprarg(e, 0), esc, ctx);
             // 2nd and 3d arguments are static
             size_t alen = jl_array_dim0(e->args);
@@ -2334,20 +2334,22 @@ static void simple_escape_analysis(jl_value_t *expr, bool esc, jl_codectx_t *ctx
             }
         }
         else if (e->head == method_sym) {
-            simple_escape_analysis(jl_exprarg(e,0), esc, ctx);
+            simple_escape_analysis(jl_exprarg(e, 0), esc, ctx);
             if (jl_expr_nargs(e) > 1) {
-                simple_escape_analysis(jl_exprarg(e,1), esc, ctx);
-                simple_escape_analysis(jl_exprarg(e,2), esc, ctx);
+                simple_escape_analysis(jl_exprarg(e, 1), esc, ctx);
+                simple_escape_analysis(jl_exprarg(e, 2), esc, ctx);
             }
         }
         else if (e->head == assign_sym) {
             // don't consider assignment LHS as a variable "use"
-            simple_escape_analysis(jl_exprarg(e,1), esc, ctx);
+            simple_escape_analysis(jl_exprarg(e, 1), esc, ctx);
         }
         else if (e->head != line_sym) {
+            if (e->head == isdefined_sym)
+                esc = false;
             size_t elen = jl_array_dim0(e->args);
-            for(i=0; i < elen; i++) {
-                simple_escape_analysis(jl_exprarg(e,i), esc, ctx);
+            for (i = 0; i < elen; i++) {
+                simple_escape_analysis(jl_exprarg(e, i), esc, ctx);
             }
         }
         return;
@@ -3603,6 +3605,67 @@ static jl_cgval_t emit_global(jl_sym_t *sym, jl_codectx_t *ctx)
     return emit_checked_var(bp, sym, ctx, false, tbaa_binding);
 }
 
+static jl_cgval_t emit_isdefined(jl_value_t *sym, jl_codectx_t *ctx)
+{
+    Value *isnull;
+    if (jl_is_slot(sym)) {
+        size_t sl = jl_slot_number(sym) - 1;
+        jl_varinfo_t &vi = ctx->slots[sl];
+        if (!vi.usedUndef)
+            return mark_julia_const(jl_true);
+        if (vi.boxroot == NULL || vi.pTIndex != NULL) {
+            assert(vi.defFlag);
+            isnull = builder.CreateLoad(vi.defFlag, vi.isVolatile);
+        }
+        if (vi.boxroot != NULL) {
+            Value *boxed = builder.CreateLoad(vi.boxroot, vi.isVolatile);
+            Value *box_isnull = builder.CreateICmpNE(boxed, V_null);
+            if (vi.pTIndex) {
+                // value is either boxed in the stack slot, or unboxed in value
+                // as indicated by testing (pTIndex & 0x80)
+                Value *tindex = builder.CreateLoad(vi.pTIndex, vi.isVolatile);
+                Value *load_unbox = builder.CreateICmpEQ(
+                            builder.CreateAnd(tindex, ConstantInt::get(T_int8, 0x80)),
+                            ConstantInt::get(T_int8, 0));
+                isnull = builder.CreateSelect(load_unbox, isnull, box_isnull);
+            }
+            else {
+                isnull = box_isnull;
+            }
+        }
+    }
+    else {
+        jl_module_t *modu;
+        jl_sym_t *name;
+        if (jl_is_globalref(sym)) {
+            modu = jl_globalref_mod(sym);
+            name = jl_globalref_name(sym);
+        }
+        else {
+            assert(jl_is_symbol(sym) && "malformed isdefined expression");
+            modu = ctx->module;
+            name = (jl_sym_t*)sym;
+        }
+        jl_binding_t *bnd = jl_get_binding(modu, name);
+        if (bnd) {
+            if (bnd->value != NULL)
+                return mark_julia_const(jl_true);
+            Value *bp = julia_binding_gv(bnd);
+            Instruction *v = builder.CreateLoad(bp);
+            tbaa_decorate(tbaa_binding, v);
+            isnull = builder.CreateICmpNE(v, V_null);
+        }
+        else {
+            Value *v = builder.CreateCall(prepare_call(jlboundp_func), {
+                    literal_pointer_val((jl_value_t*)modu),
+                    literal_pointer_val((jl_value_t*)name)
+                });
+            isnull = builder.CreateICmpNE(v, V_null);
+        }
+    }
+    return mark_julia_type(isnull, false, jl_bool_type, ctx);
+}
+
 static jl_cgval_t emit_local(jl_value_t *slotload, jl_codectx_t *ctx)
 {
     size_t sl = jl_slot_number(slotload) - 1;
@@ -4131,7 +4194,10 @@ static jl_cgval_t emit_expr(jl_value_t *expr, jl_codectx_t *ctx)
     // this is object-disoriented.
     // however, this is a good way to do it because it should *not* be easy
     // to add new node types.
-    if (head == invoke_sym) {
+    if (head == isdefined_sym) {
+        return emit_isdefined(args[0], ctx);
+    }
+    else if (head == invoke_sym) {
         return emit_invoke(ex, ctx);
     }
     else if (head == call_sym) {
@@ -6774,6 +6840,12 @@ static void init_julia_llvm_env(Module *m)
                          "jl_get_binding_or_error", m);
     add_named_global(jlgetbindingorerror_func, &jl_get_binding_or_error);
 
+    jlboundp_func =
+        Function::Create(FunctionType::get(T_pjlvalue, args_2ptrs, false),
+                         Function::ExternalLinkage,
+                         "jl_boundp", m);
+    add_named_global(jlboundp_func, &jl_boundp);
+
     builtin_func_map[jl_f_is] = jlcall_func_to_llvm("jl_f_is", &jl_f_is, m);
     builtin_func_map[jl_f_typeof] = jlcall_func_to_llvm("jl_f_typeof", &jl_f_typeof, m);
     builtin_func_map[jl_f_sizeof] = jlcall_func_to_llvm("jl_f_sizeof", &jl_f_sizeof, m);

src/dump.c

@@ -3347,7 +3347,7 @@ void jl_init_serializer(void)
 
                      jl_emptysvec, jl_emptytuple, jl_false, jl_true, jl_nothing, jl_any_type,
                      call_sym, invoke_sym, goto_ifnot_sym, return_sym, body_sym, line_sym,
-                     lambda_sym, jl_symbol("tuple"), assign_sym,
+                     lambda_sym, jl_symbol("tuple"), assign_sym, isdefined_sym,
 
                      // empirical list of very common symbols
                      #include "common_symbols1.inc"

src/interpreter.c

@@ -203,33 +203,46 @@ static jl_value_t *eval(jl_value_t *e, interpreter_state *s)
         ssize_t n = jl_slot_number(e);
         if (src == NULL || n > jl_source_nslots(src) || n < 1 || s->locals == NULL)
             jl_error("access to invalid slot number");
-        jl_value_t *v = s->locals[n-1];
+        jl_value_t *v = s->locals[n - 1];
         if (v == NULL)
             jl_undefined_var_error((jl_sym_t*)jl_array_ptr_ref(src->slotnames, n - 1));
         return v;
     }
     if (jl_is_globalref(e)) {
-        jl_sym_t *s = jl_globalref_name(e);
-        jl_value_t *v = jl_get_global(jl_globalref_mod(e), s);
-        if (v == NULL)
-            jl_undefined_var_error(s);
-        return v;
+        return jl_eval_global_var(jl_globalref_mod(e), jl_globalref_name(e));
     }
     if (jl_is_quotenode(e))
         return jl_fieldref(e,0);
     jl_module_t *modu = s->module;
     if (jl_is_symbol(e)) {  // bare symbols appear in toplevel exprs not wrapped in `thunk`
-        jl_value_t *v = jl_get_global(modu, (jl_sym_t*)e);
-        if (v == NULL)
-            jl_undefined_var_error((jl_sym_t*)e);
-        return v;
+        return jl_eval_global_var(modu, (jl_sym_t*)e);
     }
     if (!jl_is_expr(e))
         return e;
     jl_expr_t *ex = (jl_expr_t*)e;
     jl_value_t **args = (jl_value_t**)jl_array_data(ex->args);
     size_t nargs = jl_array_len(ex->args);
-    if (ex->head == call_sym) {
+    if (ex->head == isdefined_sym) {
+        jl_value_t *sym = args[0];
+        int defined = 0;
+        if (jl_is_slot(sym)) {
+            ssize_t n = jl_slot_number(sym);
+            if (src == NULL || n > jl_source_nslots(src) || n < 1 || s->locals == NULL)
+                jl_error("access to invalid slot number");
+            defined = s->locals[n - 1] != NULL;
+        }
+        else if (jl_is_globalref(sym)) {
+            defined = jl_boundp(jl_globalref_mod(sym), jl_globalref_name(sym));
+        }
+        else if (jl_is_symbol(sym)) {
+            defined = jl_boundp(modu, (jl_sym_t*)sym);
+        }
+        else {
+            assert(0 && "malformed isdefined expression");
+        }
+        return defined ? jl_true : jl_false;
+    }
+    else if (ex->head == call_sym) {
         return do_call(args, nargs, s);
     }
     else if (ex->head == invoke_sym) {

src/jitlayers.cpp

@@ -1048,7 +1048,7 @@ GlobalVariable *jl_emit_sysimg_slot(Module *m, Type *typ, const char *name,
     return gv;
 }
 
-void* jl_get_global(GlobalVariable *gv)
+void* jl_get_globalvar(GlobalVariable *gv)
 {
 #if defined(USE_MCJIT) || defined(USE_ORCJIT)
     void *p = (void*)(intptr_t)jl_ExecutionEngine->getPointerToGlobalIfAvailable(gv);

src/jitlayers.h

@@ -68,7 +68,7 @@ void addOptimizationPasses(PassManager *PM);
 void* jl_emit_and_add_to_shadow(GlobalVariable *gv, void *gvarinit = NULL);
 GlobalVariable *jl_emit_sysimg_slot(Module *m, Type *typ, const char *name,
                                     uintptr_t init, size_t &idx);
-void* jl_get_global(GlobalVariable *gv);
+void* jl_get_globalvar(GlobalVariable *gv);
 GlobalVariable *jl_get_global_for(const char *cname, void *addr, Module *M);
 void jl_add_to_shadow(Module *m);
 void jl_init_function(Function *f);

src/julia-syntax.scm

@@ -3597,6 +3597,7 @@ f(x) = yt(x)
             ((local) #f)
             ((implicit-global) #f)
             ((const) (emit e))
+            ((isdefined) (if tail (emit-return e) e))
 
             ;; top level expressions returning values
             ((abstract_type bits_type composite_type thunk toplevel module)

src/julia_internal.h

@@ -975,6 +975,7 @@ extern jl_sym_t *meta_sym; extern jl_sym_t *list_sym;
 extern jl_sym_t *inert_sym; extern jl_sym_t *static_parameter_sym;
 extern jl_sym_t *polly_sym; extern jl_sym_t *inline_sym;
 extern jl_sym_t *propagate_inbounds_sym;
+extern jl_sym_t *isdefined_sym;
 
 #ifdef __cplusplus
 }

test/core.jl

@@ -4997,3 +4997,43 @@ end
 end
 @test M22026.foofunction(Int16) === Int16
 @test M22026.foofunction2(3) === 6.0f0
+
+# tests for isdefined behavior and code generation
+global undefined_variable
+@test @isdefined Test
+@test !@isdefined undefined_variable
+@test !@isdefined undefined_variable2
+@test let local_undef, local_def = 1
+    !@isdefined local_undef
+    @isdefined local_def
+end
+f_isdefined_latedef() = @isdefined f_isdefined_def
+@test !f_isdefined_latedef()
+f_isdefined(x) = @isdefined x
+f_isdefined_undef() = @isdefined x_isundef
+f_isdefined_def() = @isdefined f_isdefined_def
+@test f_isdefined(1)
+@test f_isdefined("")
+@test !f_isdefined_undef()
+@test f_isdefined_def()
+@test f_isdefined_latedef()
+f_isdefined_defvarI() = (x = rand(Int); @isdefined x)
+f_isdefined_defvarS() = (x = randstring(1); @isdefined x)
+@test f_isdefined_defvarI()
+@test f_isdefined_defvarS()
+f_isdefined_undefvar() = (local x; @isdefined x)
+@test !f_isdefined_undefvar()
+f_isdefined_unionvar(y, t) = (t > 0 && (x = (t == 1 ? 1 : y)); @isdefined x)
+@test f_isdefined_unionvar(nothing, 1)
+@test f_isdefined_unionvar("", 1)
+@test f_isdefined_unionvar(1.0, 1)
+@test f_isdefined_unionvar(1, 1)
+@test !f_isdefined_unionvar(nothing, 0)
+@test !f_isdefined_unionvar("", 0)
+@test !f_isdefined_unionvar(1.0, 0)
+@test !f_isdefined_unionvar(1, 0)
+f_isdefined_splat(x...) = @isdefined x
+@test f_isdefined_splat(1, 2, 3)
+@test let err = @macroexpand @isdefined :x
+    isa(err, Expr) && err.head === :error && isa(err.args[1], MethodError)
+end