internal/core/adt: eliminate recursive processing on bottom

This saves a whole bunch of additional processing
and prevents a bunch of additional errors.

Fixes #3840
Fixes #3851

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I88899b607b9228a2070f74a7f08864d015bda690
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1212232
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>

Author: mpvl

Diff for: cue/testdata/basicrewrite/013_obj_unify.txtar

@@ -86,9 +86,6 @@ Errors:
 e: conflicting values 1 and {a:3} (mismatched types int and struct):
     ./in.cue:7:5
     ./in.cue:8:4
-e: cannot combine regular field "a" with 1:
-    ./in.cue:8:8
-    ./in.cue:7:5
 
 Result:
 (_|_){
@@ -113,34 +110,21 @@ Result:
     // [eval] e: conflicting values 1 and {a:3} (mismatched types int and struct):
     //     ./in.cue:7:5
     //     ./in.cue:8:4
-    // e: cannot combine regular field "a" with 1:
-    //     ./in.cue:8:8
-    //     ./in.cue:7:5
-    a: (int){ 3 }
+    a: (_|_){// 3
+    }
   }
 }
 -- diff/-out/evalalpha<==>+out/eval --
 diff old new
 --- old
 +++ new
-@@ -2,6 +2,9 @@
- e: conflicting values 1 and {a:3} (mismatched types int and struct):
-     ./in.cue:7:5
-     ./in.cue:8:4
-+e: cannot combine regular field "a" with 1:
-+    ./in.cue:8:8
-+    ./in.cue:7:5
- 
- Result:
- (_|_){
-@@ -26,6 +29,9 @@
+@@ -26,6 +26,7 @@
      // [eval] e: conflicting values 1 and {a:3} (mismatched types int and struct):
      //     ./in.cue:7:5
      //     ./in.cue:8:4
-+    // e: cannot combine regular field "a" with 1:
-+    //     ./in.cue:8:8
-+    //     ./in.cue:7:5
-     a: (int){ 3 }
+-    a: (int){ 3 }
++    a: (_|_){// 3
++    }
    }
  }
 -- diff/explanation --

Diff for: cue/testdata/benchmarks/issue3514.txtar

@@ -36,14 +36,14 @@ _schema: {
     #timezone: or([for i in list.Range(0, 571, 1) {"\(i)"}])
 }
 -- out/evalalpha/stats --
-Leaks:  3690
+Leaks:  3645
 Freed:  0
 Reused: 0
-Allocs: 3690
+Allocs: 3645
 Retain: 0
 
-Unifications: 114
-Conjuncts:    7138
+Unifications: 69
+Conjuncts:    7053
 Disjuncts:    2386
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
@@ -55,17 +55,17 @@ diff old new
 -Reused: 30511
 -Allocs: 608
 -Retain: 47
-+Leaks:  3690
++Leaks:  3645
 +Freed:  0
 +Reused: 0
-+Allocs: 3690
++Allocs: 3645
 +Retain: 0
 
 -Unifications: 189
 -Conjuncts:    92950
 -Disjuncts:    31139
-+Unifications: 114
-+Conjuncts:    7138
++Unifications: 69
++Conjuncts:    7053
 +Disjuncts:    2386
 -- out/eval/stats --
 Leaks:  27