Optimization for non-union invariant parameter.

Author: N5N3

src/subtype.c

@@ -1437,11 +1437,44 @@ static int _local_forall_exists_subtype(jl_value_t *x, jl_value_t *y, jl_stenv_t
     return sub;
 }
 
+static int obviously_nounion(jl_value_t *x, jl_stenv_t *e, jl_typeenv_t *log) JL_NOTSAFEPOINT
+{
+    if (x == NULL || x == (jl_value_t*)jl_any_type || x == jl_bottom_type)
+        return 1;
+    if (jl_is_unionall(x))
+        return obviously_nounion(((jl_unionall_t *)x)->body, e, log);
+    if (jl_is_datatype(x)) {
+        jl_datatype_t *xd = (jl_datatype_t *)x;
+        for (int i = 0; i < jl_nparams(xd); i++) {
+            jl_value_t *param = jl_tparam(xd, i);
+            if (jl_is_vararg(param))
+                param = jl_unwrap_vararg(param);
+            if (!obviously_nounion(param, e, log))
+                return 0;
+        }
+        return 1;
+    }
+    if (!jl_is_typevar(x))
+        return 0;
+    jl_typeenv_t *t = log;
+    while (t != NULL) {
+        if (x == (jl_value_t *)t->var)
+            return 0;
+        t = t->prev;
+    }
+    jl_typeenv_t newlog = { (jl_tvar_t*)x, NULL, log };
+    jl_varbinding_t *xb = lookup(e, (jl_tvar_t *)x);
+    return obviously_nounion(xb ? xb->lb : ((jl_tvar_t *)x)->lb, e, &newlog) &&
+           obviously_nounion(xb ? xb->ub : ((jl_tvar_t *)x)->ub, e, &newlog);
+}
+
 static int local_forall_exists_subtype(jl_value_t *x, jl_value_t *y, jl_stenv_t *e, int param, int limit_slow)
 {
     int16_t oldRmore = e->Runions.more;
     int sub;
-    if (pick_union_decision(e, 1) == 0) {
+    if (obviously_nounion(y, e, NULL))
+        sub = _local_forall_exists_subtype(x, y, e, param);
+    else if (pick_union_decision(e, 1) == 0) {
         jl_saved_unionstate_t oldRunions; push_unionstate(&oldRunions, &e->Runions);
         e->Lunions.used = e->Runions.used = 0;
         e->Lunions.depth = e->Runions.depth = 0;

test/subtype.jl

@@ -2436,3 +2436,7 @@ let A = Tuple{Type{T}, T} where T,
     C = Tuple{Type{MyType47877{W, V} where V<:Union{MyAbstract47877{W}, Base.BitInteger}}, MyType47877{W, V} where V<:Union{MyAbstract47877{W}, Base.BitInteger}} where W<:Base.BitInteger
     @test typeintersect(B, A) == C
 end
+
+let a = (isodd(i) ? Pair{Char, String} : Pair{String, String} for i in 1:2000)
+    @test Tuple{Type{Pair{Union{Char, String}, String}}, a...} <: Tuple{Type{Pair{K, V}}, Vararg{Pair{A, B} where B where A}} where V where K
+end