internal/core/adt: rewrite replaceIDs to scale better

https://github.com/Caascad/unity-tests is an archived CUE project
part of the Unity test suite, and I noticed that while it is pretty fast
on evalv2:

    > CUE_EXPERIMENT=evalv3=0 /bin/time cue vet -c=false
    11.35user 0.28system 0:03.83elapsed 303%CPU (0avgtext+0avgdata 752148maxresident)k

it is much slower on evalv3, and it's due to 33s spent on closedness:

    > /bin/time cue vet -c=false
    37.59user 0.71system 0:34.27elapsed 111%CPU (0avgtext+0avgdata 2690860maxresident)k
    > CUE_DEBUG=opendef /bin/time cue vet -c=false
    3.96user 0.34system 0:01.46elapsed 294%CPU (0avgtext+0avgdata 1437052maxresident)k

Rewrite the algorithm to replace recursion with a breadth-first search,
and building up a map upfront so that we can do lookups without needing
to do linear searches inside loops. This results in the 33s spent in
closedness being cut by two thirds to about 11s:

    > /bin/time cue vet -c=false
    16.72user 0.69system 0:12.66elapsed 137%CPU (0avgtext+0avgdata 2950188maxresident)k

Note that two test outputs are reordered due to swapping DFS for BFS.

Also note that the CloseIDElems changes are due to the old algorithm
incrementing the counter even when an element is marked via deleteID.
The new algorithm skips those elements upfront, so the counter
is not incremented for them.

This algorithm refactor was done with assistance from Gemini 2.5 Pro,
which had to be nudged a few times to avoid test failures.
I tweaked it quite a lot to ensure that memory reuse is preserved,
to avoid unnecessary steps such as sorting the results,
and to ensure that the "embed" logic is kept exactly as it was before.

The new algorithm also uses more maps and slices, so we also expand
OpContext from one to three fields to hold memory so that it can be
reused between calls to replaceIDs. This helps reduce the memory usage
on the project above with the new algorithm from ~10GiB to ~5GiB,
avoiding a regression in the memory usage of closedness.

Updates #3881.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I714c26af22967ff89c9f0f242e027608d596f8fb
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1217153
Reviewed-by: Marcel van Lohuizen <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mvdan

cue/testdata/benchmarks/issue1684.txtar

@@ -72,7 +72,7 @@ Unifications: 5541
 Conjuncts:    25871
 Disjuncts:    6534
 
-CloseIDElems: 85837
+CloseIDElems: 74207
 NumCloseIDs: 4115
 -- out/evalalpha --
 (struct){
@@ -159,7 +159,7 @@ diff old new
 +Conjuncts:    25871
 +Disjuncts:    6534
 +
-+CloseIDElems: 85837
++CloseIDElems: 74207
 +NumCloseIDs: 4115
 -- diff/-out/evalalpha<==>+out/eval --
 diff old new

cue/testdata/benchmarks/issue2176.txtar

@@ -68,7 +68,7 @@ Unifications: 377
 Conjuncts:    1333
 Disjuncts:    8
 
-CloseIDElems: 20071
+CloseIDElems: 20070
 NumCloseIDs: 535
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
@@ -97,7 +97,7 @@ diff old new
 +Conjuncts:    1333
 +Disjuncts:    8
 +
-+CloseIDElems: 20071
++CloseIDElems: 20070
 +NumCloseIDs: 535
 -- out/eval/stats --
 Leaks:  90

cue/testdata/benchmarks/issue3514.txtar

@@ -46,7 +46,7 @@ Unifications: 69
 Conjuncts:    7053
 Disjuncts:    2386
 
-CloseIDElems: 92
+CloseIDElems: 77
 NumCloseIDs: 5733
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
@@ -72,7 +72,7 @@ diff old new
 +Conjuncts:    7053
 +Disjuncts:    2386
 +
-+CloseIDElems: 92
++CloseIDElems: 77
 +NumCloseIDs: 5733
 -- out/eval/stats --
 Leaks:  27

cue/testdata/benchmarks/issue3633.txtar

@@ -10,7 +10,7 @@ Unifications: 667
 Conjuncts:    2680
 Disjuncts:    1955
 
-CloseIDElems: 7234
+CloseIDElems: 6838
 NumCloseIDs: 53
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
@@ -34,7 +34,7 @@ diff old new
 +Conjuncts:    2680
 +Disjuncts:    1955
 +
-+CloseIDElems: 7234
++CloseIDElems: 6838
 +NumCloseIDs: 53
 -- out/eval/stats --
 Leaks:  0

cue/testdata/benchmarks/listdedup.txtar

@@ -43,7 +43,7 @@ Unifications: 40
 Conjuncts:    98
 Disjuncts:    24
 
-CloseIDElems: 1206
+CloseIDElems: 1092
 NumCloseIDs: 22
 -- out/evalalpha --
 (struct){
@@ -486,7 +486,7 @@ diff old new
 +Conjuncts:    98
 +Disjuncts:    24
 +
-+CloseIDElems: 1206
++CloseIDElems: 1092
 +NumCloseIDs: 22
 -- out/eval/stats --
 Leaks:  0

cue/testdata/benchmarks/typocheck.txtar

@@ -31,7 +31,7 @@ Unifications: 703
 Conjuncts:    1305
 Disjuncts:    0
 
-CloseIDElems: 45090
+CloseIDElems: 43902
 NumCloseIDs: 212
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
@@ -60,7 +60,7 @@ diff old new
 +Conjuncts:    1305
 +Disjuncts:    0
 +
-+CloseIDElems: 45090
++CloseIDElems: 43902
 +NumCloseIDs: 212
 -- out/eval/stats --
 Leaks:  0

cue/testdata/builtins/closed.txtar

@@ -102,7 +102,7 @@ Unifications: 230
 Conjuncts:    360
 Disjuncts:    12
 
-CloseIDElems: 2194
+CloseIDElems: 1773
 NumCloseIDs: 106
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
@@ -128,7 +128,7 @@ diff old new
 +Conjuncts:    360
 +Disjuncts:    12
 +
-+CloseIDElems: 2194
++CloseIDElems: 1773
 +NumCloseIDs: 106
 -- out/eval/stats --
 Leaks:  61

cue/testdata/builtins/matchn.txtar

@@ -356,7 +356,7 @@ Unifications: 931
 Conjuncts:    1511
 Disjuncts:    16
 
-CloseIDElems: 1371
+CloseIDElems: 1170
 NumCloseIDs: 483
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
@@ -382,7 +382,7 @@ diff old new
 +Conjuncts:    1511
 +Disjuncts:    16
 +
-+CloseIDElems: 1371
++CloseIDElems: 1170
 +NumCloseIDs: 483
 -- out/eval/stats --
 Leaks:  52

cue/testdata/compile/scope.txtar

@@ -88,7 +88,7 @@ Unifications: 22
 Conjuncts:    39
 Disjuncts:    2
 
-CloseIDElems: 120
+CloseIDElems: 116
 NumCloseIDs: 13
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
@@ -114,7 +114,7 @@ diff old new
 +Conjuncts:    39
 +Disjuncts:    2
 +
-+CloseIDElems: 120
++CloseIDElems: 116
 +NumCloseIDs: 13
 -- out/eval/stats --
 Leaks:  2

cue/testdata/comprehensions/issue3929.txtar

@@ -97,7 +97,7 @@ Unifications: 97
 Conjuncts:    266
 Disjuncts:    53
 
-CloseIDElems: 1972
+CloseIDElems: 1903
 NumCloseIDs: 101
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
@@ -126,7 +126,7 @@ diff old new
 +Conjuncts:    266
 +Disjuncts:    53
 +
-+CloseIDElems: 1972
++CloseIDElems: 1903
 +NumCloseIDs: 101
 -- out/eval/stats --
 Leaks:  3