Allow constant-propagation to be disabled (JuliaLang#42125)

Our heuristics for constant propagation are imperfect (and probably
never will be perfect), and I've now seen many examples of
methods that no developer would ask to have const-propped get
that treatment. In some cases the cost for latency/precompilation
is very large. This renames `@aggressive_constprop` to `@constprop`
and allows two settings, `:aggressive` and `:none`.

Closes JuliaLang#38983

Co-authored-by: Shuhei Kadowaki <[email protected]>
Co-authored-by: Martin Holters <[email protected]>

base/char.jl

@@ -45,10 +45,10 @@ represents a valid Unicode character.
 """
 Char
 
-@aggressive_constprop (::Type{T})(x::Number) where {T<:AbstractChar} = T(UInt32(x))
-@aggressive_constprop AbstractChar(x::Number) = Char(x)
-@aggressive_constprop (::Type{T})(x::AbstractChar) where {T<:Union{Number,AbstractChar}} = T(codepoint(x))
-@aggressive_constprop (::Type{T})(x::AbstractChar) where {T<:Union{Int32,Int64}} = codepoint(x) % T
+@constprop :aggressive (::Type{T})(x::Number) where {T<:AbstractChar} = T(UInt32(x))
+@constprop :aggressive AbstractChar(x::Number) = Char(x)
+@constprop :aggressive (::Type{T})(x::AbstractChar) where {T<:Union{Number,AbstractChar}} = T(codepoint(x))
+@constprop :aggressive (::Type{T})(x::AbstractChar) where {T<:Union{Int32,Int64}} = codepoint(x) % T
 (::Type{T})(x::T) where {T<:AbstractChar} = x
 
 """
@@ -75,7 +75,7 @@ return a different-sized integer (e.g. `UInt8`).
 """
 function codepoint end
 
-@aggressive_constprop codepoint(c::Char) = UInt32(c)
+@constprop :aggressive codepoint(c::Char) = UInt32(c)
 
 struct InvalidCharError{T<:AbstractChar} <: Exception
     char::T
@@ -124,7 +124,7 @@ See also [`decode_overlong`](@ref) and [`show_invalid`](@ref).
 """
 isoverlong(c::AbstractChar) = false
 
-@aggressive_constprop function UInt32(c::Char)
+@constprop :aggressive function UInt32(c::Char)
     # TODO: use optimized inline LLVM
     u = bitcast(UInt32, c)
     u < 0x80000000 && return u >> 24
@@ -148,7 +148,7 @@ that support overlong encodings should implement `Base.decode_overlong`.
 """
 function decode_overlong end
 
-@aggressive_constprop function decode_overlong(c::Char)
+@constprop :aggressive function decode_overlong(c::Char)
     u = bitcast(UInt32, c)
     l1 = leading_ones(u)
     t0 = trailing_zeros(u) & 56
@@ -158,7 +158,7 @@ function decode_overlong end
     ((u & 0x007f0000) >> 4) | ((u & 0x7f000000) >> 6)
 end
 
-@aggressive_constprop function Char(u::UInt32)
+@constprop :aggressive function Char(u::UInt32)
     u < 0x80 && return bitcast(Char, u << 24)
     u < 0x00200000 || throw_code_point_err(u)
     c = ((u << 0) & 0x0000003f) | ((u << 2) & 0x00003f00) |
@@ -169,14 +169,14 @@ end
     bitcast(Char, c)
 end
 
-@aggressive_constprop @noinline UInt32_cold(c::Char) = UInt32(c)
-@aggressive_constprop function (T::Union{Type{Int8},Type{UInt8}})(c::Char)
+@constprop :aggressive @noinline UInt32_cold(c::Char) = UInt32(c)
+@constprop :aggressive function (T::Union{Type{Int8},Type{UInt8}})(c::Char)
     i = bitcast(Int32, c)
     i ≥ 0 ? ((i >>> 24) % T) : T(UInt32_cold(c))
 end
 
-@aggressive_constprop @noinline Char_cold(b::UInt32) = Char(b)
-@aggressive_constprop function Char(b::Union{Int8,UInt8})
+@constprop :aggressive @noinline Char_cold(b::UInt32) = Char(b)
+@constprop :aggressive function Char(b::Union{Int8,UInt8})
     0 ≤ b ≤ 0x7f ? bitcast(Char, (b % UInt32) << 24) : Char_cold(UInt32(b))
 end
 

base/compiler/abstractinterpretation.jl

@@ -572,6 +572,10 @@ function maybe_get_const_prop_profitable(interp::AbstractInterpreter, result::Me
         return nothing
     end
     method = match.method
+    if method.constprop == 0x02
+        add_remark!(interp, sv, "[constprop] Disabled by method parameter")
+        return nothing
+    end
     force = force_const_prop(interp, f, method)
     force || const_prop_entry_heuristic(interp, result, sv) || return nothing
     nargs::Int = method.nargs
@@ -653,7 +657,7 @@ function is_allconst(argtypes::Vector{Any})
 end
 
 function force_const_prop(interp::AbstractInterpreter, @nospecialize(f), method::Method)
-    return method.aggressive_constprop ||
+    return method.constprop == 0x01 ||
            InferenceParams(interp).aggressive_constant_propagation ||
            istopfunction(f, :getproperty) ||
            istopfunction(f, :setproperty!)

base/expr.jl

@@ -349,16 +349,26 @@ macro pure(ex)
 end
 
 """
-    @aggressive_constprop ex
-    @aggressive_constprop(ex)
-
-`@aggressive_constprop` requests more aggressive interprocedural constant
-propagation for the annotated function. For a method where the return type
-depends on the value of the arguments, this can yield improved inference results
-at the cost of additional compile time.
-"""
-macro aggressive_constprop(ex)
-    esc(isa(ex, Expr) ? pushmeta!(ex, :aggressive_constprop) : ex)
+    @constprop setting ex
+    @constprop(setting, ex)
+
+`@constprop` controls the mode of interprocedural constant propagation for the
+annotated function. Two `setting`s are supported:
+
+- `@constprop :aggressive ex`: apply constant propagation aggressively.
+  For a method where the return type depends on the value of the arguments,
+  this can yield improved inference results at the cost of additional compile time.
+- `@constprop :none ex`: disable constant propagation. This can reduce compile
+  times for functions that Julia might otherwise deem worthy of constant-propagation.
+  Common cases are for functions with `Bool`- or `Symbol`-valued arguments or keyword arguments.
+"""
+macro constprop(setting, ex)
+    if isa(setting, QuoteNode)
+        setting = setting.value
+    end
+    setting === :aggressive && return esc(isa(ex, Expr) ? pushmeta!(ex, :aggressive_constprop) : ex)
+    setting === :none && return esc(isa(ex, Expr) ? pushmeta!(ex, :no_constprop) : ex)
+    throw(ArgumentError("@constprop $setting not supported"))
 end
 
 """

src/ast.c

@@ -59,7 +59,7 @@ jl_sym_t *static_parameter_sym; jl_sym_t *inline_sym;
 jl_sym_t *noinline_sym; jl_sym_t *generated_sym;
 jl_sym_t *generated_only_sym; jl_sym_t *isdefined_sym;
 jl_sym_t *propagate_inbounds_sym; jl_sym_t *specialize_sym;
-jl_sym_t *aggressive_constprop_sym;
+jl_sym_t *aggressive_constprop_sym; jl_sym_t *no_constprop_sym;
 jl_sym_t *nospecialize_sym; jl_sym_t *macrocall_sym;
 jl_sym_t *colon_sym; jl_sym_t *hygienicscope_sym;
 jl_sym_t *throw_undef_if_not_sym; jl_sym_t *getfield_undefref_sym;
@@ -399,6 +399,7 @@ void jl_init_common_symbols(void)
     polly_sym = jl_symbol("polly");
     propagate_inbounds_sym = jl_symbol("propagate_inbounds");
     aggressive_constprop_sym = jl_symbol("aggressive_constprop");
+    no_constprop_sym = jl_symbol("no_constprop");
     isdefined_sym = jl_symbol("isdefined");
     nospecialize_sym = jl_symbol("nospecialize");
     specialize_sym = jl_symbol("specialize");

src/dump.c

@@ -671,7 +671,7 @@ static void jl_serialize_value_(jl_serializer_state *s, jl_value_t *v, int as_li
         write_int8(s->s, m->isva);
         write_int8(s->s, m->pure);
         write_int8(s->s, m->is_for_opaque_closure);
-        write_int8(s->s, m->aggressive_constprop);
+        write_int8(s->s, m->constprop);
         jl_serialize_value(s, (jl_value_t*)m->slot_syms);
         jl_serialize_value(s, (jl_value_t*)m->roots);
         jl_serialize_value(s, (jl_value_t*)m->ccallable);
@@ -1525,7 +1525,7 @@ static jl_value_t *jl_deserialize_value_method(jl_serializer_state *s, jl_value_
     m->isva = read_int8(s->s);
     m->pure = read_int8(s->s);
     m->is_for_opaque_closure = read_int8(s->s);
-    m->aggressive_constprop = read_int8(s->s);
+    m->constprop = read_int8(s->s);
     m->slot_syms = jl_deserialize_value(s, (jl_value_t**)&m->slot_syms);
     jl_gc_wb(m, m->slot_syms);
     m->roots = (jl_array_t*)jl_deserialize_value(s, (jl_value_t**)&m->roots);

src/ircode.c

@@ -381,6 +381,17 @@ static void jl_encode_value_(jl_ircode_state *s, jl_value_t *v, int as_literal)
     }
 }
 
+static jl_code_info_flags_t code_info_flags(uint8_t pure, uint8_t propagate_inbounds, uint8_t inlineable, uint8_t inferred, uint8_t constprop)
+{
+    jl_code_info_flags_t flags;
+    flags.bits.pure = pure;
+    flags.bits.propagate_inbounds = propagate_inbounds;
+    flags.bits.inlineable = inlineable;
+    flags.bits.inferred = inferred;
+    flags.bits.constprop = constprop;
+    return flags;
+}
+
 // --- decoding ---
 
 static jl_value_t *jl_decode_value(jl_ircode_state *s) JL_GC_DISABLED;
@@ -702,12 +713,8 @@ JL_DLLEXPORT jl_array_t *jl_compress_ir(jl_method_t *m, jl_code_info_t *code)
         jl_current_task->ptls
     };
 
-    uint8_t flags = (code->aggressive_constprop << 4)
-                  | (code->inferred << 3)
-                  | (code->inlineable << 2)
-                  | (code->propagate_inbounds << 1)
-                  | (code->pure << 0);
-    write_uint8(s.s, flags);
+    jl_code_info_flags_t flags = code_info_flags(code->pure, code->propagate_inbounds, code->inlineable, code->inferred, code->constprop);
+    write_uint8(s.s, flags.packed);
 
     size_t nslots = jl_array_len(code->slotflags);
     assert(nslots >= m->nargs && nslots < INT32_MAX); // required by generated functions
@@ -787,12 +794,13 @@ JL_DLLEXPORT jl_code_info_t *jl_uncompress_ir(jl_method_t *m, jl_code_instance_t
     };
 
     jl_code_info_t *code = jl_new_code_info_uninit();
-    uint8_t flags = read_uint8(s.s);
-    code->aggressive_constprop = !!(flags & (1 << 4));
-    code->inferred = !!(flags & (1 << 3));
-    code->inlineable = !!(flags & (1 << 2));
-    code->propagate_inbounds = !!(flags & (1 << 1));
-    code->pure = !!(flags & (1 << 0));
+    jl_code_info_flags_t flags;
+    flags.packed = read_uint8(s.s);
+    code->constprop = flags.bits.constprop;
+    code->inferred = flags.bits.inferred;
+    code->inlineable = flags.bits.inlineable;
+    code->propagate_inbounds = flags.bits.propagate_inbounds;
+    code->pure = flags.bits.pure;
 
     size_t nslots = read_int32(&src);
     code->slotflags = jl_alloc_array_1d(jl_array_uint8_type, nslots);
@@ -847,26 +855,29 @@ JL_DLLEXPORT uint8_t jl_ir_flag_inferred(jl_array_t *data)
     if (jl_is_code_info(data))
         return ((jl_code_info_t*)data)->inferred;
     assert(jl_typeis(data, jl_array_uint8_type));
-    uint8_t flags = ((uint8_t*)data->data)[0];
-    return !!(flags & (1 << 3));
+    jl_code_info_flags_t flags;
+    flags.packed = ((uint8_t*)data->data)[0];
+    return flags.bits.inferred;
 }
 
 JL_DLLEXPORT uint8_t jl_ir_flag_inlineable(jl_array_t *data)
 {
     if (jl_is_code_info(data))
         return ((jl_code_info_t*)data)->inlineable;
     assert(jl_typeis(data, jl_array_uint8_type));
-    uint8_t flags = ((uint8_t*)data->data)[0];
-    return !!(flags & (1 << 2));
+    jl_code_info_flags_t flags;
+    flags.packed = ((uint8_t*)data->data)[0];
+    return flags.bits.inlineable;
 }
 
 JL_DLLEXPORT uint8_t jl_ir_flag_pure(jl_array_t *data)
 {
     if (jl_is_code_info(data))
         return ((jl_code_info_t*)data)->pure;
     assert(jl_typeis(data, jl_array_uint8_type));
-    uint8_t flags = ((uint8_t*)data->data)[0];
-    return !!(flags & (1 << 0));
+    jl_code_info_flags_t flags;
+    flags.packed = ((uint8_t*)data->data)[0];
+    return flags.bits.pure;
 }
 
 JL_DLLEXPORT jl_value_t *jl_compress_argnames(jl_array_t *syms)

src/jltypes.c

@@ -2348,7 +2348,7 @@ void jl_init_types(void) JL_GC_DISABLED
                             "inlineable",
                             "propagate_inbounds",
                             "pure",
-                            "aggressive_constprop"),
+                            "constprop"),
                         jl_svec(19,
                             jl_array_any_type,
                             jl_array_int32_type,
@@ -2368,7 +2368,7 @@ void jl_init_types(void) JL_GC_DISABLED
                             jl_bool_type,
                             jl_bool_type,
                             jl_bool_type,
-                            jl_bool_type),
+                            jl_uint8_type),
                         jl_emptysvec,
                         0, 1, 19);
 
@@ -2401,7 +2401,7 @@ void jl_init_types(void) JL_GC_DISABLED
                             "isva",
                             "pure",
                             "is_for_opaque_closure",
-                            "aggressive_constprop"),
+                            "constprop"),
                         jl_svec(26,
                             jl_symbol_type,
                             jl_module_type,
@@ -2428,7 +2428,7 @@ void jl_init_types(void) JL_GC_DISABLED
                             jl_bool_type,
                             jl_bool_type,
                             jl_bool_type,
-                            jl_bool_type),
+                            jl_uint8_type),
                         jl_emptysvec,
                         0, 1, 10);
 

src/julia.h

@@ -278,7 +278,8 @@ typedef struct _jl_code_info_t {
     uint8_t inlineable;
     uint8_t propagate_inbounds;
     uint8_t pure;
-    uint8_t aggressive_constprop;
+    // uint8 settings
+    uint8_t constprop; // 0 = use heuristic; 1 = aggressive; 2 = none
 } jl_code_info_t;
 
 // This type describes a single method definition, and stores data
@@ -326,7 +327,8 @@ typedef struct _jl_method_t {
     uint8_t isva;
     uint8_t pure;
     uint8_t is_for_opaque_closure;
-    uint8_t aggressive_constprop;
+    // uint8 settings
+    uint8_t constprop;     // 0x00 = use heuristic; 0x01 = aggressive; 0x02 = none
 
 // hidden fields:
     // lock for modifications to the method

src/julia_internal.h

@@ -475,9 +475,24 @@ STATIC_INLINE jl_value_t *undefref_check(jl_datatype_t *dt, jl_value_t *v) JL_NO
     return v;
 }
 
+// -- helper types -- //
+
+typedef struct {
+    uint8_t pure:1;
+    uint8_t propagate_inbounds:1;
+    uint8_t inlineable:1;
+    uint8_t inferred:1;
+    uint8_t constprop:2; // 0 = use heuristic; 1 = aggressive; 2 = none
+} jl_code_info_flags_bitfield_t;
+
+typedef union {
+    jl_code_info_flags_bitfield_t bits;
+    uint8_t packed;
+} jl_code_info_flags_t;
 
 // -- functions -- //
 
+// jl_code_info_flag_t code_info_flags(uint8_t pure, uint8_t propagate_inbounds, uint8_t inlineable, uint8_t inferred, uint8_t constprop);
 jl_code_info_t *jl_type_infer(jl_method_instance_t *li, size_t world, int force);
 jl_code_instance_t *jl_compile_method_internal(jl_method_instance_t *meth JL_PROPAGATES_ROOT, size_t world);
 jl_code_instance_t *jl_generate_fptr(jl_method_instance_t *mi JL_PROPAGATES_ROOT, size_t world);
@@ -1376,7 +1391,7 @@ extern jl_sym_t *static_parameter_sym; extern jl_sym_t *inline_sym;
 extern jl_sym_t *noinline_sym; extern jl_sym_t *generated_sym;
 extern jl_sym_t *generated_only_sym; extern jl_sym_t *isdefined_sym;
 extern jl_sym_t *propagate_inbounds_sym; extern jl_sym_t *specialize_sym;
-extern jl_sym_t *aggressive_constprop_sym;
+extern jl_sym_t *aggressive_constprop_sym; extern jl_sym_t *no_constprop_sym;
 extern jl_sym_t *nospecialize_sym; extern jl_sym_t *macrocall_sym;
 extern jl_sym_t *colon_sym; extern jl_sym_t *hygienicscope_sym;
 extern jl_sym_t *throw_undef_if_not_sym; extern jl_sym_t *getfield_undefref_sym;

src/method.c

@@ -303,7 +303,9 @@ static void jl_code_info_set_ir(jl_code_info_t *li, jl_expr_t *ir)
                 else if (ma == (jl_value_t*)propagate_inbounds_sym)
                     li->propagate_inbounds = 1;
                 else if (ma == (jl_value_t*)aggressive_constprop_sym)
-                    li->aggressive_constprop = 1;
+                    li->constprop = 1;
+                else if (ma == (jl_value_t*)no_constprop_sym)
+                    li->constprop = 2;
                 else
                     jl_array_ptr_set(meta, ins++, ma);
             }
@@ -443,7 +445,7 @@ JL_DLLEXPORT jl_code_info_t *jl_new_code_info_uninit(void)
     src->propagate_inbounds = 0;
     src->pure = 0;
     src->edges = jl_nothing;
-    src->aggressive_constprop = 0;
+    src->constprop = 0;
     return src;
 }
 
@@ -630,7 +632,7 @@ static void jl_method_set_source(jl_method_t *m, jl_code_info_t *src)
     }
     m->called = called;
     m->pure = src->pure;
-    m->aggressive_constprop = src->aggressive_constprop;
+    m->constprop = src->constprop;
     jl_add_function_name_to_lineinfo(src, (jl_value_t*)m->name);
 
     jl_array_t *copy = NULL;
@@ -746,7 +748,7 @@ JL_DLLEXPORT jl_method_t *jl_new_method_uninit(jl_module_t *module)
     m->primary_world = 1;
     m->deleted_world = ~(size_t)0;
     m->is_for_opaque_closure = 0;
-    m->aggressive_constprop = 0;
+    m->constprop = 0;
     JL_MUTEX_INIT(&m->writelock);
     return m;
 }