planner: unify OR type IndexMerge code paths

pkg/planner/cardinality/testdata/cardinality_suite_out.json

@@ -1483,12 +1483,24 @@
             "expr": "((a < 5)) or ((a > 10 and true))",
             "row_count": 6
           },
+          {
+            "table_name": "t",
+            "type": "Index Stats-Range",
+            "expr": "((a < 5))",
+            "row_count": 6
+          },
           {
             "table_name": "t",
             "type": "Index Stats-Range",
             "expr": "((a < 5)) or ((a > 10 and true))",
             "row_count": 6
           },
+          {
+            "table_name": "t",
+            "type": "Index Stats-Range",
+            "expr": "((a > 10 and true))",
+            "row_count": 1
+          },
           {
             "table_name": "t",
             "type": "Table Stats-Expression-CNF",

pkg/planner/core/casetest/hint/testdata/integration_suite_out.json

@@ -128,12 +128,12 @@
         "Plan": [
           "PartitionUnion 33.00 root  ",
           "├─IndexMerge 11.00 root  type: union",
-          "│ ├─TableRangeScan(Build) 1.00 cop[tikv] table:t, partition:p0 range:[1,1], keep order:false, stats:pseudo",
           "│ ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p0, index:b(b) range:[2,2], keep order:false, stats:pseudo",
+          "│ ├─TableRangeScan(Build) 1.00 cop[tikv] table:t, partition:p0 range:[1,1], keep order:false, stats:pseudo",
           "│ └─TableRowIDScan(Probe) 11.00 cop[tikv] table:t, partition:p0 keep order:false, stats:pseudo",
           "├─IndexMerge 11.00 root  type: union",
-          "│ ├─TableRangeScan(Build) 1.00 cop[tikv] table:t, partition:p1 range:[1,1], keep order:false, stats:pseudo",
           "│ ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p1, index:b(b) range:[2,2], keep order:false, stats:pseudo",
+          "│ ├─TableRangeScan(Build) 1.00 cop[tikv] table:t, partition:p1 range:[1,1], keep order:false, stats:pseudo",
           "│ └─TableRowIDScan(Probe) 11.00 cop[tikv] table:t, partition:p1 keep order:false, stats:pseudo",
           "└─TableReader 11.00 root  MppVersion: 2, data:ExchangeSender",
           "  └─ExchangeSender 11.00 mpp[tiflash]  ExchangeType: PassThrough",

pkg/planner/core/find_best_task.go

@@ -945,7 +945,7 @@ func matchPropForIndexMergeAlternatives(ds *logicalop.DataSource, path *util.Acc
 			// if matchIdxes greater than 1, we should sort this match alternative path by its CountAfterAccess.
 			alternatives := oneORBranch
 			slices.SortStableFunc(matchIdxes, func(a, b int) int {
-				res := cmpAlternativesByRowCount(alternatives[a], alternatives[b])
+				res := cmpAlternatives(ds.SCtx().GetSessionVars())(alternatives[a], alternatives[b])
 				if res != 0 {
 					return res
 				}
@@ -1033,27 +1033,6 @@ func matchPropForIndexMergeAlternatives(ds *logicalop.DataSource, path *util.Acc
 			break
 		}
 	}
-	pushDownCtx := util.GetPushDownCtx(ds.SCtx())
-	for _, path := range determinedIndexPartialPaths {
-		// If any partial path contains table filters, we need to keep the whole DNF filter in the Selection.
-		if len(path.TableFilters) > 0 {
-			if !expression.CanExprsPushDown(pushDownCtx, path.TableFilters, kv.TiKV) {
-				// if this table filters can't be pushed down, all of them should be kept in the table side, cleaning the lookup side here.
-				path.TableFilters = nil
-			}
-			shouldKeepCurrentFilter = true
-		}
-		// If any partial path's index filter cannot be pushed to TiKV, we should keep the whole DNF filter.
-		if len(path.IndexFilters) != 0 && !expression.CanExprsPushDown(pushDownCtx, path.IndexFilters, kv.TiKV) {
-			shouldKeepCurrentFilter = true
-			// Clear IndexFilter, the whole filter will be put in indexMergePath.TableFilters.
-			path.IndexFilters = nil
-		}
-	}
-	// Keep this filter as a part of table filters for safety if it has any parameter.
-	if expression.MaybeOverOptimized4PlanCache(ds.SCtx().GetExprCtx(), []expression.Expression{path.IndexMergeORSourceFilter}) {
-		shouldKeepCurrentFilter = true
-	}
 	if shouldKeepCurrentFilter {
 		// add the cnf expression back as table filer.
 		indexMergePath.TableFilters = append(indexMergePath.TableFilters, path.IndexMergeORSourceFilter)