From 4904a68d31cf69d30e08c1f735b00dec3cdd2356 Mon Sep 17 00:00:00 2001
From: CEL Dev Team <cel-dev@google.com>
Date: Fri, 4 Sep 2026 02:34:48 -0700
Subject: [PATCH] Avoid re-checking the AST in CelOptimizer if it was not
 modified.

PiperOrigin-RevId: 976199136
---
 .../dev/cel/optimizer/CelOptimizerImpl.java   | 21 +++++++++-------
 .../SubexpressionOptimizerTest.java           | 25 +++++++++++++++++++
 2 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/optimizer/src/main/java/dev/cel/optimizer/CelOptimizerImpl.java b/optimizer/src/main/java/dev/cel/optimizer/CelOptimizerImpl.java
index f5e30093a..bf42b2e60 100644
--- a/optimizer/src/main/java/dev/cel/optimizer/CelOptimizerImpl.java
+++ b/optimizer/src/main/java/dev/cel/optimizer/CelOptimizerImpl.java
@@ -39,6 +39,7 @@ final class CelOptimizerImpl implements CelOptimizer {
   }
 
   @Override
+  @SuppressWarnings("ReferenceEquality")
   public CelAbstractSyntaxTree optimize(CelAbstractSyntaxTree ast) throws CelOptimizationException {
     if (!ast.isChecked()) {
       throw new IllegalArgumentException("AST must be type-checked.");
@@ -49,16 +50,18 @@ public CelAbstractSyntaxTree optimize(CelAbstractSyntaxTree ast) throws CelOptim
     try {
       for (CelAstOptimizer optimizer : astOptimizers) {
         OptimizationResult result = optimizer.optimize(optimizedAst, celOptimizerEnv);
-        if (!result.newFunctionDecls().isEmpty() || !result.newVarDecls().isEmpty()) {
-          celOptimizerEnv =
-              celOptimizerEnv
-                  .toCelBuilder()
-                  .addVarDeclarations(result.newVarDecls())
-                  .addFunctionDeclarations(result.newFunctionDecls())
-                  .build();
+        if (result.optimizedAst() != optimizedAst) {
+          if (!result.newFunctionDecls().isEmpty() || !result.newVarDecls().isEmpty()) {
+            celOptimizerEnv =
+                celOptimizerEnv
+                    .toCelBuilder()
+                    .addVarDeclarations(result.newVarDecls())
+                    .addFunctionDeclarations(result.newFunctionDecls())
+                    .build();
+          }
+          optimizedAst = celOptimizerEnv.check(result.optimizedAst()).getAst();
+          assertAstIdCorrectness(optimizedAst);
         }
-        optimizedAst = celOptimizerEnv.check(result.optimizedAst()).getAst();
-        assertAstIdCorrectness(optimizedAst);
       }
     } catch (CelValidationException e) {
       throw new CelOptimizationException(
diff --git a/optimizer/src/test/java/dev/cel/optimizer/optimizers/SubexpressionOptimizerTest.java b/optimizer/src/test/java/dev/cel/optimizer/optimizers/SubexpressionOptimizerTest.java
index 1a36bd16b..d249c4bc6 100644
--- a/optimizer/src/test/java/dev/cel/optimizer/optimizers/SubexpressionOptimizerTest.java
+++ b/optimizer/src/test/java/dev/cel/optimizer/optimizers/SubexpressionOptimizerTest.java
@@ -702,6 +702,31 @@ public void block_lazyEvaluationContainsError_cleansUpCycleState() throws Except
     assertThat(e).hasMessageThat().doesNotContain("Cycle detected");
   }
 
+  @Test
+  public void cse_nestedMacro_noOp_assertAstIdCorrectness() throws Exception {
+    Cel cel =
+        runtimeFlavor
+            .builder()
+            .addVar("x", SimpleType.DYN)
+            .setStandardMacros(CelStandardMacro.STANDARD_MACROS)
+            .setOptions(CelOptions.current().populateMacroCalls(true).build())
+            .addCompilerLibraries(CelExtensions.comprehensions())
+            .addRuntimeLibraries(CelExtensions.comprehensions())
+            .build();
+    CelOptimizer celOptimizer =
+        CelOptimizerFactory.standardCelOptimizerBuilder(cel)
+            .addAstOptimizers(SubexpressionOptimizer.getInstance())
+            .build();
+    CelAbstractSyntaxTree ast =
+        cel.compile("[{}, {\"a\": 1}, {\"b\": 2}].filter(m, has(x.a))").getAst();
+
+    CelAbstractSyntaxTree optimizedAst = celOptimizer.optimize(ast);
+
+    assertThat(CEL_UNPARSER.unparse(optimizedAst))
+        .isEqualTo("[{}, {\"a\": 1}, {\"b\": 2}].filter(m, has(x.a))");
+    assertThat(optimizedAst).isSameInstanceAs(ast);
+  }
+
   /**
    * Converts AST containing cel.block related test functions to internal functions (e.g: cel.block
    * -> cel.@block)