SERVER-73102 [CQF] Simplify explain for evaluation of simple constants

14 files changed, 124 insertions, 259 deletions

diff --git a/src/mongo/db/exec/sbe/abt/sbe_abt_test.cpp b/src/mongo/db/exec/sbe/abt/sbe_abt_test.cpp
index 0b253533439..25013487591 100644
--- a/src/mongo/db/exec/sbe/abt/sbe_abt_test.cpp
+++ b/src/mongo/db/exec/sbe/abt/sbe_abt_test.cpp
@@ -510,8 +510,7 @@ TEST_F(NodeSBE, Lower2) {
         "|   |   Collation\n"
         "|   |       Ascending\n"
         "|   Union [{rid_1}]\n"
-        "|   Evaluation [{rid_1}]\n"
-        "|   |   Variable [rid_0]\n"
+        "|   Evaluation [{rid_1} = Variable [rid_0]]\n"
         "|   IndexScan [{'<rid>': rid_0}, scanDefName: test, indexDefName: index2, interval: {=Co"
         "nst [2]}]\n"
         "IndexScan [{'<indexKey> 0': pa, '<rid>': rid_0}, scanDefName: test, indexDefName: index1"
@@ -760,8 +759,7 @@ TEST_F(NodeSBE, SpoolFibonacci) {
         "|   |   BinaryOp [Add]\n"
         "|   |   |   Variable [valIn_prev]\n"
         "|   |   Variable [valIn]\n"
-        "|   Evaluation [{val_prev}]\n"
-        "|   |   Variable [valIn]\n"
+        "|   Evaluation [{val_prev} = Variable [valIn]]\n"
         "|   Evaluation [{it}]\n"
         "|   |   BinaryOp [Add]\n"
         "|   |   |   Const [1]\n"
@@ -771,12 +769,9 @@ TEST_F(NodeSBE, SpoolFibonacci) {
         "|   |   |   Const [10]\n"
         "|   |   Variable [itIn]\n"
         "|   SpoolConsumer [Stack, id: 1, {itIn, valIn, valIn_prev}]\n"
-        "Evaluation [{val}]\n"
-        "|   Const [1]\n"
-        "Evaluation [{val_prev}]\n"
-        "|   Const [0]\n"
-        "Evaluation [{it}]\n"
-        "|   Const [1]\n"
+        "Evaluation [{val} = Const [1]]\n"
+        "Evaluation [{val_prev} = Const [0]]\n"
+        "Evaluation [{it} = Const [1]]\n"
         "LimitSkip [limit: 1, skip: 0]\n"
         "CoScan []\n",
         tree);
diff --git a/src/mongo/db/query/cost_model/cost_estimator_impl.cpp b/src/mongo/db/query/cost_model/cost_estimator_impl.cpp
index 9f797997727..6daf1d972d7 100644
--- a/src/mongo/db/query/cost_model/cost_estimator_impl.cpp
+++ b/src/mongo/db/query/cost_model/cost_estimator_impl.cpp
@@ -30,6 +30,8 @@
 #include "mongo/db/query/cost_model/cost_estimator_impl.h"
 
 #include "mongo/db/query/optimizer/defs.h"
+#include "mongo/db/query/optimizer/utils/path_utils.h"
+
 
 namespace mongo::cost_model {
 
@@ -119,7 +121,7 @@ public:
     CostAndCEInternal operator()(const ABT& /*n*/, const FilterNode& node) {
         CostAndCEInternal childResult = deriveChild(node.getChild(), 0);
         double filterCost = childResult._cost;
-        if (!isTrivialExpr<EvalFilter>(node.getFilter())) {
+        if (getTrivialExprPtr<EvalFilter>(node.getFilter()).empty()) {
             // Non-trivial filter.
             filterCost += _coefficients.getFilterStartupCost() +
                 _coefficients.getFilterIncrementalCost() * childResult._ce._value;
@@ -130,7 +132,7 @@ public:
     CostAndCEInternal operator()(const ABT& /*n*/, const EvaluationNode& node) {
         CostAndCEInternal childResult = deriveChild(node.getChild(), 0);
         double evalCost = childResult._cost;
-        if (!isTrivialExpr<EvalPath>(node.getProjection())) {
+        if (getTrivialExprPtr<EvalPath>(node.getProjection()).empty()) {
             // Non-trivial projection.
             evalCost += _coefficients.getEvalStartupCost() +
                 _coefficients.getEvalIncrementalCost() * _cardinalityEstimate._value;
@@ -364,18 +366,6 @@ private:
           _nodeCEMap(nodeCEMap),
           _coefficients(coefficients) {}
 
-    template <class T>
-    static bool isTrivialExpr(const ABT& n) {
-        if (n.is<Constant>() || n.is<Variable>()) {
-            return true;
-        }
-        if (const auto* ptr = n.cast<T>(); ptr != nullptr &&
-            ptr->getPath().template is<PathIdentity>() && isTrivialExpr<T>(ptr->getInput())) {
-            return true;
-        }
-        return false;
-    }
-
     static CostAndCEInternal deriveInternal(const Metadata& metadata,
                                             const Memo& memo,
                                             const PhysProps& physProps,
diff --git a/src/mongo/db/query/cost_model/cost_model_test.cpp b/src/mongo/db/query/cost_model/cost_model_test.cpp
index 2c1a19cbfe4..b8fd107fa56 100644
--- a/src/mongo/db/query/cost_model/cost_model_test.cpp
+++ b/src/mongo/db/query/cost_model/cost_model_test.cpp
@@ -169,8 +169,7 @@ TEST(CostModel, IncreaseJoinsCost) {
             "|   |   Collation\n"
             "|   |       Ascending\n"
             "|   Union [{rid_1}]\n"
-            "|   Evaluation [{rid_1}]\n"
-            "|   |   Variable [rid_0]\n"
+            "|   Evaluation [{rid_1} = Variable [rid_0]]\n"
             "|   IndexScan [{'<rid>': rid_0}, scanDefName: c1, indexDefName: index2, interval: "
             "{=Const [2]}]\n"
             "IndexScan [{'<indexKey> 0': pa, '<rid>': rid_0}, scanDefName: c1, indexDefName: "
diff --git a/src/mongo/db/query/optimizer/explain.cpp b/src/mongo/db/query/optimizer/explain.cpp
index 581ad743da4..806771fc6e2 100644
--- a/src/mongo/db/query/optimizer/explain.cpp
+++ b/src/mongo/db/query/optimizer/explain.cpp
@@ -33,6 +33,7 @@
 #include "mongo/db/query/optimizer/cascades/rewriter_rules.h"
 #include "mongo/db/query/optimizer/defs.h"
 #include "mongo/db/query/optimizer/node.h"
+#include "mongo/db/query/optimizer/utils/path_utils.h"
 #include "mongo/util/assert_util.h"
 
 
@@ -1223,23 +1224,32 @@ public:
                              ExplainPrinter projectionResult) {
         ExplainPrinter printer("Evaluation");
         maybePrintProps(printer, node);
-        printer.separator(" [");
 
-        // The bind block (projectionResult) is empty in V1-V2 explains. In the case of the
-        // Evaluation node, the bind block may have useful information about the embedded
-        // expression, so we make sure to print the projected expression.
         if constexpr (version < ExplainVersion::V3) {
+            const ABT& expr = node.getProjection();
+
+            printer.separator(" [");
+            // The bind block (projectionResult) is empty in V1-V2 explains. In the case of the
+            // Evaluation node, the bind block may have useful information about the embedded
+            // expression, so we make sure to print the projected expression.
             printProjection(printer, node.getProjectionName());
-        }
+            if (const auto ref = getTrivialExprPtr<EvalPath>(expr); !ref.empty()) {
+                ExplainPrinter local = generate(ref);
+                printer.separator(" = ").printSingleLevel(local).separator("]");
 
-        printer.separator("]");
-        nodeCEPropsPrint(printer, n, node);
-        printer.setChildCount(2);
+                nodeCEPropsPrint(printer, n, node);
+                printer.setChildCount(1, true /*noInline*/);
+            } else {
+                printer.separator("]");
 
-        if constexpr (version < ExplainVersion::V3) {
-            auto pathPrinter = generate(node.getProjection());
-            printer.print(pathPrinter);
+                nodeCEPropsPrint(printer, n, node);
+                printer.setChildCount(2);
+
+                auto pathPrinter = generate(expr);
+                printer.print(pathPrinter);
+            }
         } else if constexpr (version == ExplainVersion::V3) {
+            nodeCEPropsPrint(printer, n, node);
             printer.fieldName("projection").print(projectionResult);
         } else {
             MONGO_UNREACHABLE;
diff --git a/src/mongo/db/query/optimizer/interval_simplify_test.cpp b/src/mongo/db/query/optimizer/interval_simplify_test.cpp
index 92aea9eec42..8bd2acf5a38 100644
--- a/src/mongo/db/query/optimizer/interval_simplify_test.cpp
+++ b/src/mongo/db/query/optimizer/interval_simplify_test.cpp
@@ -120,8 +120,7 @@ TEST_F(IntervalIntersection, SingleFieldIntersection) {
     const std::string q4Text = "{$and: [{a0: {$gt:20}}, {a0: {$lt: 20}}]}";
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{scan_0}]\n"
-        "Evaluation [{scan_0}]\n"
-        "|   Const [Nothing]\n"
+        "Evaluation [{scan_0} = Const [Nothing]]\n"
         "LimitSkip [limit: 0, skip: 0]\n"
         "CoScan []\n",
         optimizedQueryPlan(q4Text, testIndex));
@@ -146,8 +145,7 @@ TEST_F(IntervalIntersection, SingleFieldIntersection) {
         "40}}]}]}";
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{scan_0}]\n"
-        "Evaluation [{scan_0}]\n"
-        "|   Const [Nothing]\n"
+        "Evaluation [{scan_0} = Const [Nothing]]\n"
         "LimitSkip [limit: 0, skip: 0]\n"
         "CoScan []\n",
         optimizedQueryPlan(q6Text, testIndex));
@@ -158,8 +156,7 @@ TEST_F(IntervalIntersection, SingleFieldIntersection) {
         "42}}]}]}";
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{scan_0}]\n"
-        "Evaluation [{scan_0}]\n"
-        "|   Const [Nothing]\n"
+        "Evaluation [{scan_0} = Const [Nothing]]\n"
         "LimitSkip [limit: 0, skip: 0]\n"
         "CoScan []\n",
         optimizedQueryPlan(q7Text, testIndex));
@@ -178,8 +175,7 @@ TEST_F(IntervalIntersection, MultiFieldIntersection) {
         "{$and: [{a0: {$gt: 11}}, {a0: {$lt: 14}}, {b0: {$gt: 21}}, {b0: {$lt: 12}}]}";
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{scan_0}]\n"
-        "Evaluation [{scan_0}]\n"
-        "|   Const [Nothing]\n"
+        "Evaluation [{scan_0} = Const [Nothing]]\n"
         "LimitSkip [limit: 0, skip: 0]\n"
         "CoScan []\n",
         optimizedQueryPlan(q1Text, testIndex));
@@ -188,8 +184,7 @@ TEST_F(IntervalIntersection, MultiFieldIntersection) {
         "{$and: [{a0: {$gt: 14}}, {a0: {$lt: 11}}, {b0: {$gt: 12}}, {b0: {$lt: 21}}]}";
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{scan_0}]\n"
-        "Evaluation [{scan_0}]\n"
-        "|   Const [Nothing]\n"
+        "Evaluation [{scan_0} = Const [Nothing]]\n"
         "LimitSkip [limit: 0, skip: 0]\n"
         "CoScan []\n",
         optimizedQueryPlan(q2Text, testIndex));
@@ -198,8 +193,7 @@ TEST_F(IntervalIntersection, MultiFieldIntersection) {
         "{$and: [{a0: {$gt: 14}}, {a0: {$lt: 11}}, {b0: {$gt: 21}}, {b0: {$lt: 12}}]}";
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{scan_0}]\n"
-        "Evaluation [{scan_0}]\n"
-        "|   Const [Nothing]\n"
+        "Evaluation [{scan_0} = Const [Nothing]]\n"
         "LimitSkip [limit: 0, skip: 0]\n"
         "CoScan []\n",
         optimizedQueryPlan(q3Text, testIndex));
@@ -207,8 +201,7 @@ TEST_F(IntervalIntersection, MultiFieldIntersection) {
     const std::string q4Text = "{$and: [{a0: 42}, {b0: {$gt: 21}}, {b0: {$lt: 12}}]}";
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{scan_0}]\n"
-        "Evaluation [{scan_0}]\n"
-        "|   Const [Nothing]\n"
+        "Evaluation [{scan_0} = Const [Nothing]]\n"
         "LimitSkip [limit: 0, skip: 0]\n"
         "CoScan []\n",
         optimizedQueryPlan(q4Text, testIndex));
diff --git a/src/mongo/db/query/optimizer/logical_rewriter_optimizer_test.cpp b/src/mongo/db/query/optimizer/logical_rewriter_optimizer_test.cpp
index c61ffab4d4a..ca9349d915b 100644
--- a/src/mongo/db/query/optimizer/logical_rewriter_optimizer_test.cpp
+++ b/src/mongo/db/query/optimizer/logical_rewriter_optimizer_test.cpp
@@ -240,10 +240,7 @@ TEST(LogicalRewriter, FilterProjectRewrite) {
         "    EvalFilter []\n"
         "      PathIdentity []\n"
         "      Variable [P1]\n"
-        "    Evaluation [{P1}]\n"
-        "      EvalPath []\n"
-        "        PathIdentity []\n"
-        "        Variable [ptest]\n"
+        "    Evaluation [{P1} = Variable [ptest]]\n"
         "      Collation []\n"
         "        collation: \n"
         "          ptest: Ascending\n"
@@ -267,10 +264,7 @@ TEST(LogicalRewriter, FilterProjectRewrite) {
         "      EvalFilter []\n"
         "        PathIdentity []\n"
         "        Variable [P1]\n"
-        "      Evaluation [{P1}]\n"
-        "        EvalPath []\n"
-        "          PathIdentity []\n"
-        "          Variable [ptest]\n"
+        "      Evaluation [{P1} = Variable [ptest]]\n"
         "        Scan [test, {ptest}]\n",
         latest);
 }
@@ -322,21 +316,12 @@ TEST(LogicalRewriter, FilterProjectComplexRewrite) {
         "|   EvalFilter []\n"
         "|   |   Variable [p1]\n"
         "|   PathIdentity []\n"
-        "Evaluation [{p1}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{p1} = Variable [ptest]]\n"
         "Collation []\n"
         "|   |   collation: \n"
         "|   |       ptest: Ascending\n"
-        "Evaluation [{p3}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
-        "Evaluation [{p2}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{p3} = Variable [ptest]]\n"
+        "Evaluation [{p2} = Variable [ptest]]\n"
         "Scan [test, {ptest}]\n",
         rootNode);
 
@@ -366,18 +351,9 @@ TEST(LogicalRewriter, FilterProjectComplexRewrite) {
         "|   EvalFilter []\n"
         "|   |   Variable [p1]\n"
         "|   PathIdentity []\n"
-        "Evaluation [{p1}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
-        "Evaluation [{p3}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
-        "Evaluation [{p2}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{p1} = Variable [ptest]]\n"
+        "Evaluation [{p3} = Variable [ptest]]\n"
+        "Evaluation [{p2} = Variable [ptest]]\n"
         "Scan [test, {ptest}]\n",
         latest);
 }
@@ -420,18 +396,12 @@ TEST(LogicalRewriter, FilterProjectGroupRewrite) {
         "|   aggregations: \n"
         "|       [c]\n"
         "|           Variable [b]\n"
-        "Evaluation [{b}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{b} = Variable [ptest]]\n"
         "Filter []\n"
         "|   EvalFilter []\n"
         "|   |   Variable [a]\n"
         "|   PathIdentity []\n"
-        "Evaluation [{a}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{a} = Variable [ptest]]\n"
         "Scan [test, {ptest}]\n",
         latest);
 }
@@ -482,14 +452,8 @@ TEST(LogicalRewriter, FilterProjectUnwindRewrite) {
         "|   |   Variable [a]\n"
         "|   PathIdentity []\n"
         "Unwind [{a, a_pid}]\n"
-        "Evaluation [{b}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
-        "Evaluation [{a}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{b} = Variable [ptest]]\n"
+        "Evaluation [{a} = Variable [ptest]]\n"
         "Scan [test, {ptest}]\n",
         latest);
 }
@@ -527,10 +491,7 @@ TEST(LogicalRewriter, FilterProjectExchangeRewrite) {
 
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{a, b}]\n"
-        "Evaluation [{b}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{b} = Variable [ptest]]\n"
         "Exchange []\n"
         "|   |   distribution: \n"
         "|   |       type: HashPartitioning\n"
@@ -540,10 +501,7 @@ TEST(LogicalRewriter, FilterProjectExchangeRewrite) {
         "|   EvalFilter []\n"
         "|   |   Variable [a]\n"
         "|   PathIdentity []\n"
-        "Evaluation [{a}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{a} = Variable [ptest]]\n"
         "Scan [test, {ptest}]\n",
         latest);
 }
@@ -589,14 +547,8 @@ TEST(LogicalRewriter, UnwindCollationRewrite) {
         "|   |   collation: \n"
         "|   |       b: Ascending\n"
         "Unwind [{a, a_pid}]\n"
-        "Evaluation [{b}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
-        "Evaluation [{a}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{b} = Variable [ptest]]\n"
+        "Evaluation [{a} = Variable [ptest]]\n"
         "Scan [test, {ptest}]\n",
         latest);
 }
@@ -639,15 +591,9 @@ TEST(LogicalRewriter, FilterUnionReorderSingleProjection) {
         "|   PathCompare [Eq]\n"
         "|   Const [1]\n"
         "Union [{pUnion}]\n"
-        "|   Evaluation [{pUnion}]\n"
-        "|   |   EvalPath []\n"
-        "|   |   |   Variable [ptest2]\n"
-        "|   |   PathIdentity []\n"
+        "|   Evaluation [{pUnion} = Variable [ptest2]]\n"
         "|   Scan [test2, {ptest2}]\n"
-        "Evaluation [{pUnion}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest1]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{pUnion} = Variable [ptest1]]\n"
         "Scan [test1, {ptest1}]\n",
         latest);
 
@@ -669,10 +615,7 @@ TEST(LogicalRewriter, FilterUnionReorderSingleProjection) {
         "|   |   PathTraverse [1]\n"
         "|   |   PathCompare [Eq]\n"
         "|   |   Const [1]\n"
-        "|   Evaluation [{pUnion}]\n"
-        "|   |   EvalPath []\n"
-        "|   |   |   Variable [ptest2]\n"
-        "|   |   PathIdentity []\n"
+        "|   Evaluation [{pUnion} = Variable [ptest2]]\n"
         "|   Scan [test2, {ptest2}]\n"
         "Filter []\n"
         "|   EvalFilter []\n"
@@ -681,10 +624,7 @@ TEST(LogicalRewriter, FilterUnionReorderSingleProjection) {
         "|   PathTraverse [1]\n"
         "|   PathCompare [Eq]\n"
         "|   Const [1]\n"
-        "Evaluation [{pUnion}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest1]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{pUnion} = Variable [ptest1]]\n"
         "Scan [test1, {ptest1}]\n",
         latest);
 }
@@ -754,23 +694,11 @@ TEST(LogicalRewriter, MultipleFilterUnionReorder) {
         "|   PathCompare [Eq]\n"
         "|   Const [1]\n"
         "Union [{pUnion1, pUnion2}]\n"
-        "|   Evaluation [{pUnion2}]\n"
-        "|   |   EvalPath []\n"
-        "|   |   |   Variable [ptest2]\n"
-        "|   |   PathIdentity []\n"
-        "|   Evaluation [{pUnion1}]\n"
-        "|   |   EvalPath []\n"
-        "|   |   |   Variable [ptest2]\n"
-        "|   |   PathIdentity []\n"
+        "|   Evaluation [{pUnion2} = Variable [ptest2]]\n"
+        "|   Evaluation [{pUnion1} = Variable [ptest2]]\n"
         "|   Scan [test2, {ptest2}]\n"
-        "Evaluation [{pUnion2}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest1]\n"
-        "|   PathIdentity []\n"
-        "Evaluation [{pUnion1}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest1]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{pUnion2} = Variable [ptest1]]\n"
+        "Evaluation [{pUnion1} = Variable [ptest1]]\n"
         "Scan [test1, {ptest1}]\n",
         latest);
 
@@ -792,10 +720,7 @@ TEST(LogicalRewriter, MultipleFilterUnionReorder) {
         "|   |   PathTraverse [1]\n"
         "|   |   PathCompare [Eq]\n"
         "|   |   Const [1]\n"
-        "|   Evaluation [{pUnion2}]\n"
-        "|   |   EvalPath []\n"
-        "|   |   |   Variable [ptest2]\n"
-        "|   |   PathIdentity []\n"
+        "|   Evaluation [{pUnion2} = Variable [ptest2]]\n"
         "|   Filter []\n"
         "|   |   EvalFilter []\n"
         "|   |   |   Variable [pUnion1]\n"
@@ -803,10 +728,7 @@ TEST(LogicalRewriter, MultipleFilterUnionReorder) {
         "|   |   PathTraverse [1]\n"
         "|   |   PathCompare [Eq]\n"
         "|   |   Const [1]\n"
-        "|   Evaluation [{pUnion1}]\n"
-        "|   |   EvalPath []\n"
-        "|   |   |   Variable [ptest2]\n"
-        "|   |   PathIdentity []\n"
+        "|   Evaluation [{pUnion1} = Variable [ptest2]]\n"
         "|   Scan [test2, {ptest2}]\n"
         "Filter []\n"
         "|   EvalFilter []\n"
@@ -815,10 +737,7 @@ TEST(LogicalRewriter, MultipleFilterUnionReorder) {
         "|   PathTraverse [1]\n"
         "|   PathCompare [Eq]\n"
         "|   Const [1]\n"
-        "Evaluation [{pUnion2}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest1]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{pUnion2} = Variable [ptest1]]\n"
         "Filter []\n"
         "|   EvalFilter []\n"
         "|   |   Variable [pUnion1]\n"
@@ -826,10 +745,7 @@ TEST(LogicalRewriter, MultipleFilterUnionReorder) {
         "|   PathTraverse [1]\n"
         "|   PathCompare [Eq]\n"
         "|   Const [1]\n"
-        "Evaluation [{pUnion1}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest1]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{pUnion1} = Variable [ptest1]]\n"
         "Scan [test1, {ptest1}]\n",
         latest);
 }
diff --git a/src/mongo/db/query/optimizer/optimizer_test.cpp b/src/mongo/db/query/optimizer/optimizer_test.cpp
index 2b2deaca2ce..d6646b332dc 100644
--- a/src/mongo/db/query/optimizer/optimizer_test.cpp
+++ b/src/mongo/db/query/optimizer/optimizer_test.cpp
@@ -351,12 +351,9 @@ TEST(Optimizer, GroupBy) {
         "        Const [10]\n"
         "      [a2]\n"
         "        Const [11]\n"
-        "    Evaluation [{p3}]\n"
-        "      Const [3]\n"
-        "      Evaluation [{p2}]\n"
-        "        Const [2]\n"
-        "        Evaluation [{p1}]\n"
-        "          Const [1]\n"
+        "    Evaluation [{p3} = Const [3]]\n"
+        "      Evaluation [{p2} = Const [2]]\n"
+        "        Evaluation [{p1} = Const [1]]\n"
         "          Scan [test, {ptest}]\n",
         rootNode);
 
@@ -400,14 +397,11 @@ TEST(Optimizer, Union) {
     ASSERT_EXPLAIN_AUTO(
         "Root [{B, ptest}]\n"
         "  Union [{B, ptest}]\n"
-        "    Evaluation [{B}]\n"
-        "      Const [3]\n"
+        "    Evaluation [{B} = Const [3]]\n"
         "      Scan [test, {ptest}]\n"
-        "    Evaluation [{B}]\n"
-        "      Const [4]\n"
+        "    Evaluation [{B} = Const [4]]\n"
         "      Scan [test, {ptest}]\n"
-        "    Evaluation [{B}]\n"
-        "      Const [5]\n"
+        "    Evaluation [{B} = Const [5]]\n"
         "      Evaluation [{ptest}]\n"
         "        EvalPath []\n"
         "          PathConstant []\n"
diff --git a/src/mongo/db/query/optimizer/physical_rewriter_optimizer_test.cpp b/src/mongo/db/query/optimizer/physical_rewriter_optimizer_test.cpp
index 2ae1dbe73c3..ce5b4d8d398 100644
--- a/src/mongo/db/query/optimizer/physical_rewriter_optimizer_test.cpp
+++ b/src/mongo/db/query/optimizer/physical_rewriter_optimizer_test.cpp
@@ -91,10 +91,7 @@ TEST(PhysRewriter, PhysicalRewriterBasic) {
         "|   PathGet [a]\n"
         "|   PathCompare [Eq]\n"
         "|   Const [1]\n"
-        "Evaluation [{p2}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [p1]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{p2} = Variable [p1]]\n"
         "Filter []\n"
         "|   EvalFilter []\n"
         "|   |   Variable [p1]\n"
@@ -174,10 +171,7 @@ TEST(PhysRewriter, PhysicalRewriterBasic) {
         "|           type: Centralized, disableExchanges\n"
         "|       indexingRequirement: \n"
         "|           Complete, dedupRID\n"
-        "Evaluation [{p2}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [p1]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{p2} = Variable [p1]]\n"
         "Properties [cost: 0.428487, localCost: 0, adjustedCE: 100]\n"
         "|   |   Logical:\n"
         "|   |       cardinalityEstimate: \n"
@@ -280,14 +274,8 @@ TEST(PhysRewriter, GroupBy) {
         "|   aggregations: \n"
         "|       [c]\n"
         "|           Variable [b]\n"
-        "Evaluation [{b}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
-        "Evaluation [{a}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{b} = Variable [ptest]]\n"
+        "Evaluation [{a} = Variable [ptest]]\n"
         "PhysicalScan [{'<root>': ptest}, test]\n",
         optimized);
 }
@@ -341,8 +329,7 @@ TEST(PhysRewriter, GroupBy1) {
         "|   aggregations: \n"
         "|       [pb]\n"
         "|           Variable [pa]\n"
-        "Evaluation [{pa}]\n"
-        "|   Const [null]\n"
+        "Evaluation [{pa} = Const [null]]\n"
         "PhysicalScan [{}, test]\n",
         optimized);
 }
@@ -398,14 +385,8 @@ TEST(PhysRewriter, Unwind) {
         "|   |   Variable [a]\n"
         "|   PathIdentity []\n"
         "Unwind [{a, a_pid}]\n"
-        "Evaluation [{b}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
-        "Evaluation [{a}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [ptest]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{b} = Variable [ptest]]\n"
+        "Evaluation [{a} = Variable [ptest]]\n"
         "PhysicalScan [{'<root>': ptest}, test]\n",
         optimized);
 }
@@ -1222,10 +1203,7 @@ TEST(PhysRewriter, FilterIndexing5) {
         "|   |   Variable [pb]\n"
         "|   PathCompare [Gt]\n"
         "|   Const [0]\n"
-        "Evaluation [{pb}]\n"
-        "|   EvalPath []\n"
-        "|   |   Variable [evalTemp_0]\n"
-        "|   PathIdentity []\n"
+        "Evaluation [{pb} = Variable [evalTemp_0]]\n"
         "IndexScan [{'<indexKey> 0': pa, '<indexKey> 1': evalTemp_0}, scanDefName: c1, indexDefNa"
         "me: index1, interval: {>Const [0 | maxKey]}]\n",
         optimized);
@@ -1841,8 +1819,7 @@ TEST(PhysRewriter, SargableProjectionRenames) {
     // projections.
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{root}]\n"
-        "Evaluation [{pa1}]\n"
-        "|   Variable [pa]\n"
+        "Evaluation [{pa1} = Variable [pa]]\n"
         "Sargable [Complete]\n"
         "|   |   |   |   requirementsMap: \n"
         "|   |   |   |       refProjection: root, path: 'PathGet [a] PathIdentity []', boundProje"
@@ -2218,8 +2195,7 @@ TEST(PhysRewriter, EvalIndexing2) {
     // Verify collation is subsumed into the index scan.
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{pa2}]\n"
-        "Evaluation [{pa3}]\n"
-        "|   Variable [pa1]\n"
+        "Evaluation [{pa3} = Variable [pa1]]\n"
         "Evaluation [{pa2}]\n"
         "|   EvalPath []\n"
         "|   |   Const [0]\n"
@@ -2329,20 +2305,14 @@ TEST(PhysRewriter, MultiKeyIndex) {
             "|           FunctionCall [$addToSet]\n"
             "|           Variable [sideId_0]\n"
             "Union [{rid_0, sideId_0, unionTemp_0, unionTemp_1}]\n"
-            "|   Evaluation [{unionTemp_1}]\n"
-            "|   |   Variable [pb]\n"
-            "|   Evaluation [{unionTemp_0}]\n"
-            "|   |   Const [Nothing]\n"
-            "|   Evaluation [{sideId_0}]\n"
-            "|   |   Const [1]\n"
+            "|   Evaluation [{unionTemp_1} = Variable [pb]]\n"
+            "|   Evaluation [{unionTemp_0} = Const [Nothing]]\n"
+            "|   Evaluation [{sideId_0} = Const [1]]\n"
             "|   IndexScan [{'<indexKey> 0': pb, '<rid>': rid_0}, scanDefName: c1, indexDefName: "
             "index2, interval: {[Const [maxKey], Const [2])}]\n"
-            "Evaluation [{unionTemp_1}]\n"
-            "|   Const [Nothing]\n"
-            "Evaluation [{unionTemp_0}]\n"
-            "|   Variable [pa]\n"
-            "Evaluation [{sideId_0}]\n"
-            "|   Const [0]\n"
+            "Evaluation [{unionTemp_1} = Const [Nothing]]\n"
+            "Evaluation [{unionTemp_0} = Variable [pa]]\n"
+            "Evaluation [{sideId_0} = Const [0]]\n"
             "IndexScan [{'<indexKey> 0': pa, '<rid>': rid_0}, scanDefName: c1, indexDefName: "
             "index1, interval: {=Const [1]}]\n",
             optimized);
@@ -2367,8 +2337,7 @@ TEST(PhysRewriter, MultiKeyIndex) {
             "|   |   Condition\n"
             "|   |       rid_0 = rid_2\n"
             "|   Union [{rid_2}]\n"
-            "|   Evaluation [{rid_2}]\n"
-            "|   |   Variable [rid_0]\n"
+            "|   Evaluation [{rid_2} = Variable [rid_0]]\n"
             "|   IndexScan [{'<rid>': rid_0}, scanDefName: c1, indexDefName: index2, interval: "
             "{[Const [maxKey], Const [2])}, reversed]\n"
             "IndexScan [{'<rid>': rid_0}, scanDefName: c1, indexDefName: index1, interval: {=Const "
@@ -3487,8 +3456,7 @@ TEST(PhysRewriter, ElemMatchIndexNoArrays) {
     // If we do not have arrays (index is not multikey) we simplify to unsatisfiable query.
     ASSERT_EXPLAIN_V2_AUTO(
         "Root [{root}]\n"
-        "Evaluation [{root}]\n"
-        "|   Const [Nothing]\n"
+        "Evaluation [{root} = Const [Nothing]]\n"
         "LimitSkip [limit: 0, skip: 0]\n"
         "CoScan []\n",
         optimized);
@@ -3732,12 +3700,10 @@ TEST(PhysRewriter, NestedElemMatch) {
         "|       [sides_0]\n"
         "|           FunctionCall [$addToSet] Variable [sideId_0]\n"
         "Union [{rid_0, sideId_0}]\n"
-        "|   Evaluation [{sideId_0}]\n"
-        "|   |   Const [1]\n"
-        "|   IndexScan [{'<rid>': rid_0}, scanDefName: coll1, indexDefName: index1, interval: {[C"
-        "onst [[]], Const [BinData(0, )])}]\n"
-        "Evaluation [{sideId_0}]\n"
-        "|   Const [0]\n"
+        "|   Evaluation [{sideId_0} = Const [1]]\n"
+        "|   IndexScan [{'<rid>': rid_0}, scanDefName: coll1, indexDefName: index1, interval: "
+        "{[Const [[]], Const [BinData(0, )])}]\n"
+        "Evaluation [{sideId_0} = Const [0]]\n"
         "Filter []\n"
         "|   EvalFilter []\n"
         "|   |   Variable [evalTemp_3]\n"
@@ -5662,10 +5628,9 @@ TEST(PhysRewriter, PerfOnlyPreds2) {
         "|   |   Collation\n"
         "|   |       Ascending\n"
         "|   Union [{rid_5}]\n"
-        "|   Evaluation [{rid_5}]\n"
-        "|   |   Variable [rid_0]\n"
-        "|   IndexScan [{'<rid>': rid_0}, scanDefName: c1, indexDefName: index2, interval: {=Cons"
-        "t [2]}]\n"
+        "|   Evaluation [{rid_5} = Variable [rid_0]]\n"
+        "|   IndexScan [{'<rid>': rid_0}, scanDefName: c1, indexDefName: index2, interval: {=Const "
+        "[2]}]\n"
         "IndexScan [{'<rid>': rid_0}, scanDefName: c1, indexDefName: index1, interval: {=Const [1"
         "]}]\n",
         optimized);
diff --git a/src/mongo/db/query/optimizer/rewrites/path_optimizer_test.cpp b/src/mongo/db/query/optimizer/rewrites/path_optimizer_test.cpp
index d4414fc08a8..257ec2621d4 100644
--- a/src/mongo/db/query/optimizer/rewrites/path_optimizer_test.cpp
+++ b/src/mongo/db/query/optimizer/rewrites/path_optimizer_test.cpp
@@ -735,8 +735,7 @@ TEST(Path, ProjElim3) {
 
     ASSERT_EXPLAIN_AUTO(
         "Root [{p99}]\n"
-        "  Evaluation [{p99}]\n"
-        "    Variable [root]\n"
+        "  Evaluation [{p99} = Variable [root]]\n"
         "    Scan [test, {root}]\n",
         tree);
 }
diff --git a/src/mongo/db/query/optimizer/utils/path_utils.h b/src/mongo/db/query/optimizer/utils/path_utils.h
index c5e33bf6e39..17e9eefe05e 100644
--- a/src/mongo/db/query/optimizer/utils/path_utils.h
+++ b/src/mongo/db/query/optimizer/utils/path_utils.h
@@ -36,6 +36,23 @@
 namespace mongo::optimizer {
 
 /**
+ * If the input expression is a constant or a variable, or it is an EvalFilter/Path which has an
+ * identity path and input which itself is constant or variable, then return a pointer to the deepst
+ * simple expression.
+ */
+template <class T>
+ABT::reference_type getTrivialExprPtr(const ABT& n) {
+    if (n.is<Constant>() || n.is<Variable>()) {
+        return n.ref();
+    }
+    if (const auto* ptr = n.cast<T>();
+        ptr != nullptr && ptr->getPath().template is<PathIdentity>()) {
+        return getTrivialExprPtr<T>(ptr->getInput());
+    }
+    return {};
+}
+
+/**
  * Returns a vector all paths nested under conjunctions (PathComposeM) in the given path.
  * For example, PathComposeM(PathComposeM(Foo, Bar), Baz) returns [Foo, Bar, Baz].
  * If the given path is not a conjunction, returns a vector with the given path.
diff --git a/src/mongo/db/test_output/pipeline/abt/a_b_t_optimization_test/optimize_pipeline_tests.txt b/src/mongo/db/test_output/pipeline/abt/a_b_t_optimization_test/optimize_pipeline_tests.txt
index 615a43b75da..409ccab781c 100644
--- a/src/mongo/db/test_output/pipeline/abt/a_b_t_optimization_test/optimize_pipeline_tests.txt
+++ b/src/mongo/db/test_output/pipeline/abt/a_b_t_optimization_test/optimize_pipeline_tests.txt
@@ -301,8 +301,7 @@ Root [{embedProj_0}]
 Collation []
 |   |   collation: 
 |   |       sort_0: Ascending
-Evaluation [{sort_0}]
-|   Variable [unwoundProj_0]
+Evaluation [{sort_0} = Variable [unwoundProj_0]]
 Evaluation [{embedProj_0}]
 |   If []
 |   |   |   Variable [scan_0]
@@ -739,11 +738,9 @@ GroupBy [{rid_0}]
 |           FunctionCall [$addToSet]
 |           Variable [sideId_0]
 Union [{rid_0, sideId_0}]
-|   Evaluation [{sideId_0}]
-|   |   Const [1]
+|   Evaluation [{sideId_0} = Const [1]]
 |   IndexScan [{'<rid>': rid_0}, scanDefName: collection, indexDefName: index1, interval: {(Const [70], Const [""])}]
-Evaluation [{sideId_0}]
-|   Const [0]
+Evaluation [{sideId_0} = Const [0]]
 IndexScan [{'<rid>': rid_0}, scanDefName: collection, indexDefName: index1, interval: {[Const [nan], Const [90])}]
 
 
@@ -902,8 +899,7 @@ GroupBy [{groupByProj_0}]
 |       [field_agg_0]
 |           FunctionCall [$first]
 |           Variable [groupByInputProj_0]
-Evaluation [{groupByProj_0}]
-|   Const [null]
+Evaluation [{groupByProj_0} = Const [null]]
 PhysicalScan [{'b': groupByInputProj_0}, collection]
 
 
@@ -944,10 +940,7 @@ Union [{scan_0}]
 |   |   PathTraverse [1]
 |   |   PathCompare [Eq]
 |   |   Const [1]
-|   Evaluation [{scan_0}]
-|   |   EvalPath []
-|   |   |   Variable [scan_1]
-|   |   PathIdentity []
+|   Evaluation [{scan_0} = Variable [scan_1]]
 |   PhysicalScan [{'<root>': scan_1}, collB]
 Filter []
 |   EvalFilter []
@@ -1039,8 +1032,7 @@ GroupBy [{groupByProj_0}]
 |       [field_agg_0]
 |           FunctionCall [$addToSet]
 |           Variable [groupByInputProj_0]
-Evaluation [{groupByProj_0}]
-|   Const [{}]
+Evaluation [{groupByProj_0} = Const [{}]]
 PhysicalScan [{'a': groupByInputProj_0}, test]
 
 
diff --git a/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/elem_match_translation.txt b/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/elem_match_translation.txt
index 0c6d127bdf4..7bff5c24fe8 100644
--- a/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/elem_match_translation.txt
+++ b/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/elem_match_translation.txt
@@ -114,8 +114,7 @@ Evaluation [{combinedProjection_0}]
 |   |   PathConstant []
 |   |   Variable [projGetPath_0]
 |   PathKeep [_id, a]
-Evaluation [{projGetPath_0}]
-|   Const [[1, 2, 3, 4]]
+Evaluation [{projGetPath_0} = Const [[1, 2, 3, 4]]]
 Scan [collection, {scan_0}]
 
 
diff --git a/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/simple_projection_translation.txt b/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/simple_projection_translation.txt
index 17512bc1c01..1e8c394b677 100644
--- a/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/simple_projection_translation.txt
+++ b/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/simple_projection_translation.txt
@@ -132,8 +132,7 @@ Evaluation [{combinedProjection_0}]
 |   |   |   PathKeep [c]
 |   |   PathKeep [b]
 |   PathKeep [_id, a, a1]
-Evaluation [{projGetPath_0}]
-|   Const ["str"]
+Evaluation [{projGetPath_0} = Const ["str"]]
 Scan [collection, {scan_0}]
 
 
diff --git a/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/union_translation.txt b/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/union_translation.txt
index 8d9aac181d0..a35d90c7494 100644
--- a/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/union_translation.txt
+++ b/src/mongo/db/test_output/pipeline/abt/a_b_t_translation_test/union_translation.txt
@@ -31,10 +31,7 @@ Filter []
 |   PathCompare [Eq]
 |   Const [1]
 Union [{scan_0}]
-|   Evaluation [{scan_0}]
-|   |   EvalPath []
-|   |   |   Variable [scan_1]
-|   |   PathIdentity []
+|   Evaluation [{scan_0} = Variable [scan_1]]
 |   Scan [collB, {scan_1}]
 Scan [collA, {scan_0}]