gf: cache cache_with_orig decision (#48833)

Memoizing this can save a lot of repeated effort for queries such as
`@which eltype(String)`. Otherwise we repeatedly try to check if
`eltype(::Type)` is a good way to cache that result, even though it
never gets better the more we check it.

(cherry picked from commit bdcd5e2)

src/gf.c

@@ -1195,6 +1195,8 @@ static jl_method_instance_t *cache_method(
     }
     // TODO: maybe assert(jl_isa_compileable_sig(compilationsig, sparams, definition));
     newmeth = jl_specializations_get_linfo(definition, (jl_value_t*)compilationsig, sparams);
+    if (newmeth->cache_with_orig)
+        cache_with_orig = 1;
 
     jl_tupletype_t *cachett = tt;
     jl_svec_t* guardsigs = jl_emptysvec;
@@ -1261,6 +1263,10 @@ static jl_method_instance_t *cache_method(
             max_valid = max_valid2;
             cachett = compilationsig;
         }
+        else {
+            // do not revisit this decision
+            newmeth->cache_with_orig = 1;
+        }
     }
 
     // now scan `cachett` and ensure that `Type{T}` in the cache will be matched exactly by `typeof(T)`

src/jltypes.c

@@ -2531,7 +2531,7 @@ void jl_init_types(void) JL_GC_DISABLED
     jl_method_instance_type =
         jl_new_datatype(jl_symbol("MethodInstance"), core,
                         jl_any_type, jl_emptysvec,
-                        jl_perm_symsvec(9,
+                        jl_perm_symsvec(10,
                             "def",
                             "specTypes",
                             "sparam_vals",
@@ -2540,8 +2540,9 @@ void jl_init_types(void) JL_GC_DISABLED
                             "callbacks",
                             "cache",
                             "inInference",
+                            "cache_with_orig",
                             "precompiled"),
-                        jl_svec(9,
+                        jl_svec(10,
                             jl_new_struct(jl_uniontype_type, jl_method_type, jl_module_type),
                             jl_any_type,
                             jl_simplevector_type,
@@ -2550,6 +2551,7 @@ void jl_init_types(void) JL_GC_DISABLED
                             jl_any_type,
                             jl_any_type,
                             jl_bool_type,
+                            jl_bool_type,
                             jl_bool_type),
                         jl_emptysvec,
                         0, 1, 3);

src/julia.h

@@ -369,6 +369,7 @@ struct _jl_method_instance_t {
     jl_array_t *callbacks; // list of callback functions to inform external caches about invalidations
     _Atomic(struct _jl_code_instance_t*) cache;
     uint8_t inInference; // flags to tell if inference is running on this object
+    uint8_t cache_with_orig; // !cache_with_specTypes
     uint8_t precompiled; // true if this instance was generated by an explicit `precompile(...)` call
 };
 

src/method.c

@@ -447,6 +447,7 @@ JL_DLLEXPORT jl_method_instance_t *jl_new_method_instance_uninit(void)
     li->callbacks = NULL;
     jl_atomic_store_relaxed(&li->cache, NULL);
     li->inInference = 0;
+    li->inInference = 0;
     li->precompiled = 0;
     return li;
 }