Cache binding pointer in GlobalRef

On certain workloads, profiling shows a surprisingly high fraction of
inference time spent looking up bindings in modules. Bindings use
a hash table, so they're expected to be quite fast, but certainly
not zero. A big contributor to the problem is that we do basically
treat it as zero, looking up bindings for GlobalRefs multiple times
for each statement (e.g. in `isconst`, `isdefined`, to get the types,
etc). This PR attempts to improve the situation by adding an extra
field to GlobalRef that caches this lookup. This field is not serialized
and if not set, we fallback to the previous behavior. I would expect
the memory overhead to be relatively small, since we do intern GlobalRefs
in memory to only have one per binding (rather than one per use).

 # Benchmarks

The benchmarks look quite promising. Consider this artifical example
(though it's actually not all that far fetched, given some of the
generated code we see):

```
using Core.Intrinsics: add_int
const ONE = 1
@eval function f(x, y)
	z = 0
	$([:(z = add_int(x, add_int(z, ONE))) for _ = 1:10000]...)
	return add_int(z, y)
end
g(y) = f(ONE, y)
```

On master:
```
julia> @time @code_typed g(1)
  1.427227 seconds (1.31 M allocations: 58.809 MiB, 5.73% gc time, 99.96% compilation time)
CodeInfo(
1 ─ %1 = invoke Main.f(Main.ONE::Int64, y::Int64)::Int64
└──      return %1
) => Int64
```

On this PR:
```
julia> @time @code_typed g(1)
  0.503151 seconds (1.19 M allocations: 53.641 MiB, 5.10% gc time, 33.59% compilation time)
CodeInfo(
1 ─ %1 = invoke Main.f(Main.ONE::Int64, y::Int64)::Int64
└──      return %1
) => Int64
```

I don't expect the same speedup on other workloads, but there should be
a few % speedup on most workloads still.

 # Future extensions

The other motivation for this is that with a view towards #40399,
we will want to more clearly define when bindings get resolved. The
idea here would then be that binding resolution replaces generic
`GlobalRefs` by GlobalRefs with a set binding cache, and any
unresolved bindings would be treated conservatively by inference
and optimization.

base/boot.jl

@@ -412,7 +412,7 @@ eval(Core, quote
     end
     LineInfoNode(mod::Module, @nospecialize(method), file::Symbol, line::Int32, inlined_at::Int32) =
         $(Expr(:new, :LineInfoNode, :mod, :method, :file, :line, :inlined_at))
-    GlobalRef(m::Module, s::Symbol) = $(Expr(:new, :GlobalRef, :m, :s))
+    GlobalRef(m::Module, s::Symbol, binding::Ptr{Nothing}) = $(Expr(:new, :GlobalRef, :m, :s, :binding))
     SlotNumber(n::Int) = $(Expr(:new, :SlotNumber, :n))
     TypedSlot(n::Int, @nospecialize(t)) = $(Expr(:new, :TypedSlot, :n, :t))
     PhiNode(edges::Array{Int32, 1}, values::Array{Any, 1}) = $(Expr(:new, :PhiNode, :edges, :values))
@@ -812,6 +812,8 @@ Unsigned(x::Union{Float16, Float32, Float64, Bool}) = UInt(x)
 Integer(x::Integer) = x
 Integer(x::Union{Float16, Float32, Float64}) = Int(x)
 
+GlobalRef(m::Module, s::Symbol) = GlobalRef(m, s, bitcast(Ptr{Nothing}, 0))
+
 # Binding for the julia parser, called as
 #
 #    Core._parse(text, filename, lineno, offset, options)

base/compiler/abstractinterpretation.jl

@@ -1982,7 +1982,7 @@ function abstract_eval_special_value(interp::AbstractInterpreter, @nospecialize(
             return sv.argtypes[e.n]
         end
     elseif isa(e, GlobalRef)
-        return abstract_eval_global(interp, e.mod, e.name, sv)
+        return abstract_eval_globalref(interp, e, sv)
     end
 
     return Const(e)
@@ -2256,17 +2256,24 @@ function abstract_eval_statement(interp::AbstractInterpreter, @nospecialize(e),
     return rt
 end
 
-function abstract_eval_global(M::Module, s::Symbol)
-    if isdefined(M, s) && isconst(M, s)
-        return Const(getglobal(M, s))
+function isdefined_globalref(g::GlobalRef)
+    g.binding != C_NULL && return ccall(:jl_binding_boundp, Cint, (Ptr{Cvoid},), g.binding) != 0
+    return isdefined(g.mod, g.name)
+end
+
+function abstract_eval_globalref(g::GlobalRef)
+    if isdefined_globalref(g) && isconst(g)
+        g.binding != C_NULL && return Const(ccall(:jl_binding_value, Any, (Ptr{Cvoid},), g.binding))
+        return Const(getglobal(g.mod, g.name))
     end
-    ty = ccall(:jl_binding_type, Any, (Any, Any), M, s)
+    ty = ccall(:jl_binding_type, Any, (Any, Any), g.mod, g.name)
     ty === nothing && return Any
     return ty
 end
+abstract_eval_global(M::Module, s::Symbol) = abstract_eval_globalref(GlobalRef(M, s))
 
-function abstract_eval_global(interp::AbstractInterpreter, M::Module, s::Symbol, frame::Union{InferenceState, IRCode})
-    rt = abstract_eval_global(M, s)
+function abstract_eval_globalref(interp::AbstractInterpreter, g::GlobalRef, frame::Union{InferenceState, IRCode})
+    rt = abstract_eval_globalref(g)
     consistent = inaccessiblememonly = ALWAYS_FALSE
     nothrow = false
     if isa(rt, Const)
@@ -2277,7 +2284,7 @@ function abstract_eval_global(interp::AbstractInterpreter, M::Module, s::Symbol,
         else
             nothrow = true
         end
-    elseif isdefined(M,s)
+    elseif isdefined_globalref(g)
         nothrow = true
     end
     merge_effects!(interp, frame, Effects(EFFECTS_TOTAL; consistent, nothrow, inaccessiblememonly))

base/compiler/optimize.jl

@@ -335,7 +335,7 @@ function argextype(
     elseif isa(x, QuoteNode)
         return Const(x.value)
     elseif isa(x, GlobalRef)
-        return abstract_eval_global(x.mod, x.name)
+        return abstract_eval_globalref(x)
     elseif isa(x, PhiNode)
         return Any
     elseif isa(x, PiNode)

base/compiler/ssair/slot2ssa.jl

@@ -216,7 +216,7 @@ function typ_for_val(@nospecialize(x), ci::CodeInfo, sptypes::Vector{Any}, idx::
         end
         return (ci.ssavaluetypes::Vector{Any})[idx]
     end
-    isa(x, GlobalRef) && return abstract_eval_global(x.mod, x.name)
+    isa(x, GlobalRef) && return abstract_eval_globalref(x)
     isa(x, SSAValue) && return (ci.ssavaluetypes::Vector{Any})[x.id]
     isa(x, Argument) && return slottypes[x.n]
     isa(x, NewSSAValue) && return DelayedTyp(x)

base/compiler/utilities.jl

@@ -378,7 +378,7 @@ function is_throw_call(e::Expr)
     if e.head === :call
         f = e.args[1]
         if isa(f, GlobalRef)
-            ff = abstract_eval_global(f.mod, f.name)
+            ff = abstract_eval_globalref(f)
             if isa(ff, Const) && ff.val === Core.throw
                 return true
             end

base/reflection.jl

@@ -265,6 +265,11 @@ Determine whether a global is declared `const` in a given module `m`.
 isconst(m::Module, s::Symbol) =
     ccall(:jl_is_const, Cint, (Any, Any), m, s) != 0
 
+function isconst(g::GlobalRef)
+    g.binding != C_NULL && return ccall(:jl_binding_is_const, Cint, (Ptr{Cvoid},), g.binding) != 0
+    return isconst(g.mod, g.name)
+end
+
 """
     isconst(t::DataType, s::Union{Int,Symbol}) -> Bool
 

src/dump.c

@@ -2084,6 +2084,9 @@ static void jl_deserialize_struct(jl_serializer_state *s, jl_value_t *v) JL_GC_D
             entry->min_world = 1;
             entry->max_world = 0;
         }
+    } else if (dt == jl_globalref_type) {
+        jl_globalref_t *r = (jl_globalref_t*)v;
+        r->bnd_cache = jl_get_binding(r->mod, r->name);
     }
 }
 

src/jltypes.c

@@ -2392,12 +2392,6 @@ void jl_init_types(void) JL_GC_DISABLED
                         jl_svec(1, jl_slotnumber_type),
                         jl_emptysvec, 0, 0, 1);
 
-    jl_globalref_type =
-        jl_new_datatype(jl_symbol("GlobalRef"), core, jl_any_type, jl_emptysvec,
-                        jl_perm_symsvec(2, "mod", "name"),
-                        jl_svec(2, jl_module_type, jl_symbol_type),
-                        jl_emptysvec, 0, 0, 2);
-
     jl_code_info_type =
         jl_new_datatype(jl_symbol("CodeInfo"), core,
                         jl_any_type, jl_emptysvec,
@@ -2694,6 +2688,12 @@ void jl_init_types(void) JL_GC_DISABLED
 
     jl_value_t *pointer_void = jl_apply_type1((jl_value_t*)jl_pointer_type, (jl_value_t*)jl_nothing_type);
 
+    jl_globalref_type =
+        jl_new_datatype(jl_symbol("GlobalRef"), core, jl_any_type, jl_emptysvec,
+                        jl_perm_symsvec(3, "mod", "name", "binding"),
+                        jl_svec(3, jl_module_type, jl_symbol_type, pointer_void),
+                        jl_emptysvec, 0, 0, 3);
+
     tv = jl_svec2(tvar("A"), tvar("R"));
     jl_opaque_closure_type = (jl_unionall_t*)jl_new_datatype(jl_symbol("OpaqueClosure"), core, jl_function_type, tv,
         jl_perm_symsvec(5, "captures", "world", "source", "invoke", "specptr"),

src/julia.h

@@ -603,6 +603,13 @@ typedef struct _jl_module_t {
     jl_mutex_t lock;
 } jl_module_t;
 
+typedef struct {
+    jl_module_t *mod;
+    jl_sym_t *name;
+    // Not serialized. Caches the value of jl_get_binding(mod, name).
+    jl_binding_t *bnd_cache;
+} jl_globalref_t;
+
 // one Type-to-Value entry
 typedef struct _jl_typemap_entry_t {
     JL_DATA_TYPE
@@ -1626,6 +1633,8 @@ JL_DLLEXPORT int jl_boundp(jl_module_t *m, jl_sym_t *var);
 JL_DLLEXPORT int jl_defines_or_exports_p(jl_module_t *m, jl_sym_t *var);
 JL_DLLEXPORT int jl_binding_resolved_p(jl_module_t *m, jl_sym_t *var);
 JL_DLLEXPORT int jl_is_const(jl_module_t *m, jl_sym_t *var);
+JL_DLLEXPORT int jl_binding_is_const(jl_binding_t *b);
+JL_DLLEXPORT int jl_binding_boundp(jl_binding_t *b);
 JL_DLLEXPORT jl_value_t *jl_get_global(jl_module_t *m JL_PROPAGATES_ROOT, jl_sym_t *var);
 JL_DLLEXPORT void jl_set_global(jl_module_t *m JL_ROOTING_ARGUMENT, jl_sym_t *var, jl_value_t *val JL_ROOTED_ARGUMENT);
 JL_DLLEXPORT void jl_set_const(jl_module_t *m JL_ROOTING_ARGUMENT, jl_sym_t *var, jl_value_t *val JL_ROOTED_ARGUMENT);

src/module.c

@@ -413,14 +413,17 @@ JL_DLLEXPORT jl_binding_t *jl_get_binding_or_error(jl_module_t *m, jl_sym_t *var
 JL_DLLEXPORT jl_value_t *jl_module_globalref(jl_module_t *m, jl_sym_t *var)
 {
     JL_LOCK(&m->lock);
-    jl_binding_t *b = (jl_binding_t*)ptrhash_get(&m->bindings, var);
+    jl_binding_t *b = _jl_get_module_binding(m, var);
     if (b == HT_NOTFOUND) {
         JL_UNLOCK(&m->lock);
-        return jl_new_struct(jl_globalref_type, m, var);
+        return jl_new_struct(jl_globalref_type, m, var, jl_box_voidpointer(NULL));
     }
     jl_value_t *globalref = jl_atomic_load_relaxed(&b->globalref);
     if (globalref == NULL) {
-        jl_value_t *newref = jl_new_struct(jl_globalref_type, m, var);
+        jl_value_t *newref = jl_new_struct(jl_globalref_type, m, var, jl_box_voidpointer(NULL));
+        if (b->owner) {
+            ((jl_globalref_t*)newref)->bnd_cache = b->owner == m ? b : _jl_get_module_binding(b->owner, var);
+        }
         if (jl_atomic_cmpswap_relaxed(&b->globalref, &globalref, newref)) {
             JL_GC_PROMISE_ROOTED(newref);
             globalref = newref;
@@ -662,12 +665,18 @@ JL_DLLEXPORT jl_binding_t *jl_get_module_binding(jl_module_t *m JL_PROPAGATES_RO
     return b == HT_NOTFOUND ? NULL : b;
 }
 
+
+JL_DLLEXPORT jl_value_t *jl_binding_value(jl_binding_t *b JL_PROPAGATES_ROOT)
+{
+    return b->value;
+}
+
 JL_DLLEXPORT jl_value_t *jl_get_global(jl_module_t *m, jl_sym_t *var)
 {
     jl_binding_t *b = jl_get_binding(m, var);
     if (b == NULL) return NULL;
     if (b->deprecated) jl_binding_deprecation_warning(m, b);
-    return b->value;
+    return jl_binding_value(b);
 }
 
 JL_DLLEXPORT void jl_set_global(jl_module_t *m JL_ROOTING_ARGUMENT, jl_sym_t *var, jl_value_t *val JL_ROOTED_ARGUMENT)
@@ -696,10 +705,22 @@ JL_DLLEXPORT void jl_set_const(jl_module_t *m JL_ROOTING_ARGUMENT, jl_sym_t *var
               jl_symbol_name(bp->name));
 }
 
+JL_DLLEXPORT int jl_binding_is_const(jl_binding_t *b)
+{
+    assert(b);
+    return b->constp;
+}
+
+JL_DLLEXPORT int jl_binding_boundp(jl_binding_t *b)
+{
+    assert(b);
+    return b->value != 0;
+}
+
 JL_DLLEXPORT int jl_is_const(jl_module_t *m, jl_sym_t *var)
 {
     jl_binding_t *b = jl_get_binding(m, var);
-    return b && b->constp;
+    return b && jl_binding_is_const(b);
 }
 
 // set the deprecated flag for a binding:

src/staticdata.c

@@ -576,6 +576,10 @@ static void jl_serialize_value__(jl_serializer_state *s, jl_value_t *v, int recu
         jl_serialize_value(s, tn->partial);
     }
     else if (t->layout->nfields > 0) {
+        if (jl_typeis(v, jl_globalref_type)) {
+            // Don't save the cached binding reference in staticdata
+            ((jl_globalref_t*)v)->bnd_cache = NULL;
+        }
         char *data = (char*)jl_data_ptr(v);
         size_t i, np = t->layout->npointers;
         for (i = 0; i < np; i++) {