From ab41985470ba0a74e80ecfd7ec21e4d9ada428da Mon Sep 17 00:00:00 2001
From: Shahbaz Youssefi <syoussefi@chromium.org>
Date: Thu, 07 May 2026 15:25:01 -0400
Subject: [PATCH] AST: Fix variable declaration in dead code in `case`

Previously fixed for IR here:

https://chromium-review.git.corp.google.com/c/angle/angle/+/7589940

A similar transformation is applied to the AST transformation.

Bug: chromium:484756087
Change-Id: I579f839613ed5f1e05084f2b1c19bc0dbd386cbc
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/7829599
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
---

diff --git a/src/compiler/translator/tree_ops/PruneNoOps.cpp b/src/compiler/translator/tree_ops/PruneNoOps.cpp
index 367dbf3..6e832c1 100644
--- a/src/compiler/translator/tree_ops/PruneNoOps.cpp
+++ b/src/compiler/translator/tree_ops/PruneNoOps.cpp
@@ -109,18 +109,22 @@
   private:
     PruneNoOpsTraverser(TSymbolTable *symbolTable);
     bool visitDeclaration(Visit, TIntermDeclaration *node) override;
+    bool visitSwitch(Visit visit, TIntermSwitch *node) override;
     bool visitBlock(Visit visit, TIntermBlock *node) override;
     bool visitLoop(Visit visit, TIntermLoop *loop) override;
     bool visitBranch(Visit visit, TIntermBranch *node) override;
     TIntermTyped *pruneNoOpCommaExpressions(TIntermTyped *statement);
 
     bool mIsBranchVisited = false;
+
+    TVector<TVector<const TVariable *>> mSwitchPrunedDeclarationsStack;
 };
 
 bool PruneNoOpsTraverser::apply(TCompiler *compiler, TIntermBlock *root, TSymbolTable *symbolTable)
 {
     PruneNoOpsTraverser prune(symbolTable);
     root->traverse(&prune);
+    ASSERT(prune.mSwitchPrunedDeclarationsStack.empty());
     return prune.updateTree(compiler, root);
 }
 
@@ -196,6 +200,35 @@
     return false;
 }
 
+bool PruneNoOpsTraverser::visitSwitch(Visit visit, TIntermSwitch *node)
+{
+    node->getInit()->traverse(this);
+
+    // Before visiting the block, push a list of variable declarations that were pruned because they
+    // were declared directly in the body of the switch but after a branch.  The variable
+    // declarations are instead prepended to the switch, in case they are used in a later case which
+    // references them in live code.
+    mSwitchPrunedDeclarationsStack.push_back({});
+
+    node->getStatementList()->traverse(this);
+    if (!mSwitchPrunedDeclarationsStack.back().empty())
+    {
+        TIntermSequence replacement;
+        for (const TVariable *toDeclare : mSwitchPrunedDeclarationsStack.back())
+        {
+            TIntermDeclaration *decl = new TIntermDeclaration();
+            decl->appendDeclarator(new TIntermSymbol(toDeclare));
+            replacement.push_back(decl);
+        }
+        replacement.push_back(node);
+        mMultiReplacements.emplace_back(getParentNode()->getAsBlock(), node,
+                                        std::move(replacement));
+    }
+
+    mSwitchPrunedDeclarationsStack.pop_back();
+    return false;
+}
+
 bool PruneNoOpsTraverser::visitBlock(Visit visit, TIntermBlock *node)
 {
     ASSERT(visit == PreVisit);
@@ -218,6 +251,42 @@
         // If a branch is visited, prune the statement.  If the statement is a no-op, also prune it.
         if (mIsBranchVisited || IsNoOp(statement))
         {
+            // If this is a declaration, remember the variable.  The declaration is moved to before
+            // the switch, to support cases like:
+            //
+            //    switch(u0){
+            //        case 0:
+            //            break;
+            //            vec4 d = vec4(0);
+            //        default:
+            //            d.a = .0;
+            //    }
+            if (mIsBranchVisited && getParentNode()->getAsSwitchNode() != nullptr)
+            {
+                TIntermDeclaration *decl = statement->getAsDeclarationNode();
+                if (decl != nullptr)
+                {
+                    for (TIntermNode *declarator : *decl->getSequence())
+                    {
+                        TIntermSymbol *symbol        = declarator->getAsSymbolNode();
+                        const TVariable *declaredVar = nullptr;
+                        if (symbol != nullptr)
+                        {
+                            declaredVar = &symbol->variable();
+                        }
+                        else
+                        {
+                            TIntermBinary *initNode = declarator->getAsBinaryNode();
+                            ASSERT(initNode && initNode->getOp() == EOpInitialize);
+                            ASSERT(initNode->getLeft()->getAsSymbolNode());
+                            declaredVar = &initNode->getLeft()->getAsSymbolNode()->variable();
+                        }
+
+                        mSwitchPrunedDeclarationsStack.back().push_back(declaredVar);
+                    }
+                }
+            }
+
             continue;
         }
 
diff --git a/src/tests/gl_tests/GLSLTest.cpp b/src/tests/gl_tests/GLSLTest.cpp
index f0d3e8f..ea13530 100644
--- a/src/tests/gl_tests/GLSLTest.cpp
+++ b/src/tests/gl_tests/GLSLTest.cpp
@@ -22759,9 +22759,6 @@
 // Test variable declaration in switch case after dead code, but used in the next case.
 TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode1)
 {
-    // The PruneNoOps AST pass does not retain the variable in dead code.
-    ANGLE_SKIP_TEST_IF(!getEGLWindow()->isFeatureEnabled(Feature::UseIr));
-
     constexpr char kFS[] = R"(#version 300 es
 precision mediump float;
 uniform int u0;
@@ -22787,9 +22784,6 @@
 // The dead code is after divergence and reconvergence.
 TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode2)
 {
-    // The PruneNoOps AST pass does not retain the variable in dead code.
-    ANGLE_SKIP_TEST_IF(!getEGLWindow()->isFeatureEnabled(Feature::UseIr));
-
     constexpr char kFS[] = R"(#version 300 es
 precision mediump float;
 uniform int u0;
@@ -22821,9 +22815,6 @@
 // The dead code itself has divergence and reconvergence.
 TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode3)
 {
-    // The PruneNoOps AST pass does not retain the variable in dead code.
-    ANGLE_SKIP_TEST_IF(!getEGLWindow()->isFeatureEnabled(Feature::UseIr));
-
     constexpr char kFS[] = R"(#version 300 es
 precision mediump float;
 uniform int u0;
@@ -22919,6 +22910,89 @@
     EXPECT_GL_NO_ERROR();
 }
 
+// Test variable declaration in switch case after dead code, but used in the next case.
+TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode6)
+{
+    constexpr char kFS[] = R"(#version 300 es
+precision mediump float;
+uniform int u0;
+out vec4 fragOut;
+void main(){
+    vec4 d = vec4(1);
+    switch(u0){
+        case 0:
+            break;
+            vec4 d = vec4(0);
+        default:
+            d.a = .0;
+    }
+    fragOut = vec4(1, 0, 0, 1);
+})";
+    ANGLE_GL_PROGRAM(program, essl3_shaders::vs::Simple(), kFS);
+    glUseProgram(program);
+    drawQuad(program, essl3_shaders::PositionAttrib(), 0.0);
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::red);
+    EXPECT_GL_NO_ERROR();
+}
+
+// Test variable declaration in switch case after dead code, but used in the next case.
+TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode7)
+{
+    constexpr char kFS[] = R"(#version 300 es
+precision mediump float;
+uniform int u0;
+out vec4 fragOut;
+void main(){
+    vec4 d = vec4(1);
+    switch(u0){
+        case 0:
+            break;
+            vec4 d = vec4(0), d1 = vec4(0);

diff --git a/src/tests/gl_tests/GLSLTest.cpp b/src/tests/gl_tests/GLSLTest.cpp
index f0d3e8f..ea13530 100644
--- a/src/tests/gl_tests/GLSLTest.cpp
+++ b/src/tests/gl_tests/GLSLTest.cpp
@@ -22759,9 +22759,6 @@
 // Test variable declaration in switch case after dead code, but used in the next case.
 TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode1)
 {
-    // The PruneNoOps AST pass does not retain the variable in dead code.
-    ANGLE_SKIP_TEST_IF(!getEGLWindow()->isFeatureEnabled(Feature::UseIr));
-
     constexpr char kFS[] = R"(#version 300 es
 precision mediump float;
 uniform int u0;
@@ -22787,9 +22784,6 @@
 // The dead code is after divergence and reconvergence.
 TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode2)
 {
-    // The PruneNoOps AST pass does not retain the variable in dead code.
-    ANGLE_SKIP_TEST_IF(!getEGLWindow()->isFeatureEnabled(Feature::UseIr));
-
     constexpr char kFS[] = R"(#version 300 es
 precision mediump float;
 uniform int u0;
@@ -22821,9 +22815,6 @@
 // The dead code itself has divergence and reconvergence.
 TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode3)
 {
-    // The PruneNoOps AST pass does not retain the variable in dead code.
-    ANGLE_SKIP_TEST_IF(!getEGLWindow()->isFeatureEnabled(Feature::UseIr));
-
     constexpr char kFS[] = R"(#version 300 es
 precision mediump float;
 uniform int u0;
@@ -22919,6 +22910,89 @@
     EXPECT_GL_NO_ERROR();
 }
 
+// Test variable declaration in switch case after dead code, but used in the next case.
+TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode6)
+{
+    constexpr char kFS[] = R"(#version 300 es
+precision mediump float;
+uniform int u0;
+out vec4 fragOut;
+void main(){
+    vec4 d = vec4(1);
+    switch(u0){
+        case 0:
+            break;
+            vec4 d = vec4(0);
+        default:
+            d.a = .0;
+    }
+    fragOut = vec4(1, 0, 0, 1);
+})";
+    ANGLE_GL_PROGRAM(program, essl3_shaders::vs::Simple(), kFS);
+    glUseProgram(program);
+    drawQuad(program, essl3_shaders::PositionAttrib(), 0.0);
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::red);
+    EXPECT_GL_NO_ERROR();
+}
+
+// Test variable declaration in switch case after dead code, but used in the next case.
+TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode7)
+{
+    constexpr char kFS[] = R"(#version 300 es
+precision mediump float;
+uniform int u0;
+out vec4 fragOut;
+void main(){
+    vec4 d = vec4(1);
+    switch(u0){
+        case 0:
+            break;
+            vec4 d = vec4(0), d1 = vec4(0);
+            vec4 d2 = vec4(0);
+        default:
+            d.a = .0;
+            d1.a = .0;
+            d2.a = .0;
+    }
+    fragOut = vec4(1, 0, 0, 1);
+})";
+    ANGLE_GL_PROGRAM(program, essl3_shaders::vs::Simple(), kFS);
+    glUseProgram(program);
+    drawQuad(program, essl3_shaders::PositionAttrib(), 0.0);
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::red);
+    EXPECT_GL_NO_ERROR();
+}
+
+// Test variable declaration in switch case after dead code, but used in the next case.
+TEST_P(GLSLTest_ES3, VariableDeclaredInCaseDeadCode8)
+{
+    constexpr char kFS[] = R"(#version 300 es
+precision mediump float;
+uniform int u0;
+out vec4 fragOut;
+void main(){
+    switch(u0){
+        case 0:
+            break;
+            switch(u0){
+                case 0:
+                    break;
+                    vec4 d = vec4(0);
+                default:
+                    d.a = .0;
+            }
+        default:
+            break;
+    }
+    fragOut = vec4(1, 0, 0, 1);
+})";
+    ANGLE_GL_PROGRAM(program, essl3_shaders::vs::Simple(), kFS);
+    glUseProgram(program);
+    drawQuad(program, essl3_shaders::PositionAttrib(), 0.0);
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::red);
+    EXPECT_GL_NO_ERROR();
+}
+
 // Test that a for loop initializer can be a variable with a struct declaration.
 TEST_P(GLSLTest_ES31, StructDeclarationInForLoop)
 {