Add a @compile directive to disable interpreter (JuliaLang#42128)

We currently use a `while false; end` hack to disable to interpreter,
and this is getting more widely used outside of base. Unfortunately,
improvements to the interpreter that would allow us to interpret loops
would defeat the intention. This allows developers to annotate blocks
with `@compile` to specify that they want to force the compiler to run
on this block.

base/expr.jl

@@ -374,6 +374,13 @@ macro propagate_inbounds(ex)
  esc(ex)
 end
 
+"""
+ @compile
+
+Force compilation of the block or function (Julia's built-in interpreter is blocked from executing it).
+"""
+macro compile() Expr(:meta, :compile) end
+
 """
  @polly
 

base/timing.jl

@@ -203,7 +203,7 @@ julia> @time begin
 """
 macro time(ex)
  quote
- while false; end # compiler heuristic: compile this block (alter this if the heuristic changes)
+ @compile
  local stats = gc_num()
  local elapsedtime = time_ns()
  local compile_elapsedtime = cumulative_compile_time_ns_before()
@@ -249,7 +249,7 @@ pool allocs: 1
 """
 macro timev(ex)
  quote
- while false; end # compiler heuristic: compile this block (alter this if the heuristic changes)
+ @compile
  local stats = gc_num()
  local elapsedtime = time_ns()
  local compile_elapsedtime = cumulative_compile_time_ns_before()
@@ -282,7 +282,7 @@ julia> @elapsed sleep(0.3)
 """
 macro elapsed(ex)
  quote
- while false; end # compiler heuristic: compile this block (alter this if the heuristic changes)
+ @compile
  local t0 = time_ns()
  $(esc(ex))
  (time_ns() - t0) / 1e9
@@ -314,7 +314,7 @@ julia> @allocated rand(10^6)
 """
 macro allocated(ex)
  quote
- while false; end # compiler heuristic: compile this block (alter this if the heuristic changes)
+ @compile
  local b0 = Ref{Int64}(0)
  local b1 = Ref{Int64}(0)
  gc_bytes(b0)
@@ -362,7 +362,7 @@ julia> stats.gcstats.total_time
 """
 macro timed(ex)
  quote
- while false; end # compiler heuristic: compile this block (alter this if the heuristic changes)
+ @compile
  local stats = gc_num()
  local elapsedtime = time_ns()
  local val = $(esc(ex))

src/toplevel.c

@@ -378,6 +378,8 @@ int jl_code_requires_compiler(jl_code_info_t *src)
  assert(jl_typeis(body, jl_array_any_type));
  size_t i;
  int has_intrinsics = 0, has_defs = 0, has_opaque = 0;
+ if (jl_has_meta(body, compile_sym))
+ return 1;
  for(i=0; i < jl_array_len(body); i++) {
  jl_value_t *stmt = jl_array_ptr_ref(body,i);
  expr_attributes(stmt, &has_intrinsics, &has_defs, &has_opaque);
@@ -387,7 +389,7 @@ int jl_code_requires_compiler(jl_code_info_t *src)
  return 0;
 }
 
-static void body_attributes(jl_array_t *body, int *has_intrinsics, int *has_defs, int *has_loops, int *has_opaque)
+static void body_attributes(jl_array_t *body, int *has_intrinsics, int *has_defs, int *has_loops, int *has_opaque, int *has_compile)
 {
  size_t i;
  *has_loops = 0;
@@ -405,6 +407,7 @@ static void body_attributes(jl_array_t *body, int *has_intrinsics, int *has_defs
  }
  expr_attributes(stmt, has_intrinsics, has_defs, has_opaque);
  }
+ *has_compile = jl_has_meta(body, compile_sym);
 }
 
 static jl_module_t *call_require(jl_module_t *mod, jl_sym_t *var) JL_GLOBALLY_ROOTED
@@ -848,19 +851,20 @@ jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int
  return (jl_value_t*)ex;
  }
 
- int has_intrinsics = 0, has_defs = 0, has_loops = 0, has_opaque = 0;
+ int has_intrinsics = 0, has_defs = 0, has_loops = 0, has_opaque = 0, has_compile = 0;
  assert(head == thunk_sym);
  thk = (jl_code_info_t*)jl_exprarg(ex, 0);
  assert(jl_is_code_info(thk));
  assert(jl_typeis(thk->code, jl_array_any_type));
- body_attributes((jl_array_t*)thk->code, &has_intrinsics, &has_defs, &has_loops, &has_opaque);
+ body_attributes((jl_array_t*)thk->code, &has_intrinsics, &has_defs, &has_loops, &has_opaque, &has_compile);
 
  jl_value_t *result;
  if (has_intrinsics || (!has_defs && fast && has_loops &&
  jl_options.compile_enabled != JL_OPTIONS_COMPILE_OFF &&
  jl_options.compile_enabled != JL_OPTIONS_COMPILE_MIN &&
  jl_get_module_compile(m) != JL_OPTIONS_COMPILE_OFF &&
- jl_get_module_compile(m) != JL_OPTIONS_COMPILE_MIN)) {
+ jl_get_module_compile(m) != JL_OPTIONS_COMPILE_MIN) ||
+ has_compile) {
  // use codegen
  mfunc = method_instance_for_thunk(thk, m);
  jl_resolve_globals_in_ir((jl_array_t*)thk->code, m, NULL, 0);