From 10dcf44dc8e0d44596fa5a999117a04fddfcab8b Mon Sep 17 00:00:00 2001
From: Shahbaz Youssefi <syoussefi@chromium.org>
Date: Mon, 20 Jul 2026 14:21:15 -0400
Subject: [PATCH] Translator: Disallow gl_Clip/CullDistance declaration after use

If these built-ins are redeclared after being referenced, the AST
inconsistently uses two TVariables to refer to the built-in.

This could potentially be fixed by a pass over the AST.  With IR, it
should be easier to support by simply sizing the existing VariableID.
However, support for this use case requires additional validation to
ensure that the implicitly derived size for these built-ins is no bigger
than the redeclared size.

Bug: angleproject:42266961
Bug: chromium:536444272
Bug: chromium:536681676
Change-Id: I1d8faa95280b5183a9581447051364cfc96479b7
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/8123200
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Alexey Knyazev <lexa.knyazev@gmail.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
---

diff --git a/src/compiler/translator/ParseContext.cpp b/src/compiler/translator/ParseContext.cpp
index 7745cbe..623f1cb 100644
--- a/src/compiler/translator/ParseContext.cpp
+++ b/src/compiler/translator/ParseContext.cpp
@@ -281,6 +281,11 @@
     return IsSampler(type->getBasicType()) || type->isStructureContainingOnlySamplers();
 }
 
+bool IsClipCullEncountered(const ClipCullDistanceInfo &info)
+{
+    return info.maxIndex >= 0 || info.hasNonConstIndex || info.hasArrayLengthMethodCall;
+}
+
 void MarkClipCullFirstEncounter(const TSourceLoc &line, ClipCullDistanceInfo *info)
 {
     if (info->firstEncounter.first_line < 0)
@@ -2346,12 +2351,29 @@
             }
         }
 
+        // Record the redeclared size of gl_Clip/CullDistance.  Do not allow redeclaration after
+        // these built-ins are already referenced to avoid having to fix the AST after the fact.
+        // With IR, this could be more easily supported if needed.
         switch (expectedType.getQualifier())
         {
             case EvqClipDistance:
+                if (IsClipCullEncountered(mClipDistanceInfo))
+                {
+                    error(line,
+                          "redeclaration of gl_ClipDistance after it is referenced is not allowed",
+                          identifier);
+                    return false;
+                }
                 MarkClipCullRedeclaredSize(line, type->getOutermostArraySize(), &mClipDistanceInfo);
                 break;
             case EvqCullDistance:
+                if (IsClipCullEncountered(mCullDistanceInfo))
+                {
+                    error(line,
+                          "redeclaration of gl_CullDistance after it is referenced is not allowed",
+                          identifier);
+                    return false;
+                }
                 MarkClipCullRedeclaredSize(line, type->getOutermostArraySize(), &mCullDistanceInfo);
                 break;
             default:
diff --git a/src/tests/gl_tests/GLSLValidationTest.cpp b/src/tests/gl_tests/GLSLValidationTest.cpp
index 28a44aa..dc5e920 100644
--- a/src/tests/gl_tests/GLSLValidationTest.cpp
+++ b/src/tests/gl_tests/GLSLValidationTest.cpp
@@ -7060,6 +7060,278 @@
     }
 }
 
+// Shader redeclares gl_ClipDistance, but after it's been referenced with a constant index.
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareClipDistanceAfterReferenceConstantIndex)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+void main()
+{
+    gl_Position = aPosition;
+    gl_ClipDistance[0] = 1.0;
+}
+out highp float gl_ClipDistance[3];
+)";
+    constexpr char kExpect[] =
+        "'gl_ClipDistance' : redeclaration of gl_ClipDistance after it is referenced is not "
+        "allowed";
+
+    if (hasAngle)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
+// Shader redeclares gl_CullDistance, but after it's been referenced with a constant index.
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareCullDistanceAfterReferenceConstantIndex)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+void main()
+{
+    gl_Position = aPosition;
+    gl_CullDistance[0] = 1.0;
+}
+out highp float gl_CullDistance[3];
+)";
+    constexpr char kExpect[] =
+        "'gl_CullDistance' : redeclaration of gl_CullDistance after it is referenced is not "
+        "allowed";
+
+    if (hasAngle)
+    {
+        GLint maxCullDistances = 0;
+        glGetIntegerv(GL_MAX_CULL_DISTANCES_EXT, &maxCullDistances);
+        if (maxCullDistances > 0)
+        {
+            validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+        }
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
+// Shader redeclares gl_ClipDistance, but after it's been referenced with a non-constant index.
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareClipDistanceAfterReferenceNonConstantIndex)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+void main()
+{
+    gl_Position = aPosition;
+    for (int i = 0; i < 2; ++i)
+    {
+        gl_ClipDistance[i] = 1.0;
+    }
+}
+out highp float gl_ClipDistance[3];
+)";
+    constexpr char kExpect[] =
+        "'gl_ClipDistance' : redeclaration of gl_ClipDistance after it is referenced is not "
+        "allowed";
+
+    if (hasAngle)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
+// Shader redeclares gl_CullDistance, but after it's been referenced with a non-constant index.
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareCullDistanceAfterReferenceNonConstantIndex)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+void main()
+{
+    gl_Position = aPosition;
+    for (int i = 0; i < 2; ++i)
+    {
+        gl_CullDistance[i] = 1.0;
+    }
+}
+out highp float gl_CullDistance[3];
+)";
+    constexpr char kExpect[] =
+        "'gl_CullDistance' : redeclaration of gl_CullDistance after it is referenced is not "

diff --git a/src/tests/gl_tests/GLSLValidationTest.cpp b/src/tests/gl_tests/GLSLValidationTest.cpp
index 28a44aa..dc5e920 100644
--- a/src/tests/gl_tests/GLSLValidationTest.cpp
+++ b/src/tests/gl_tests/GLSLValidationTest.cpp
@@ -7060,6 +7060,278 @@
     }
 }
 
+// Shader redeclares gl_ClipDistance, but after it's been referenced with a constant index.
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareClipDistanceAfterReferenceConstantIndex)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+void main()
+{
+    gl_Position = aPosition;
+    gl_ClipDistance[0] = 1.0;
+}
+out highp float gl_ClipDistance[3];
+)";
+    constexpr char kExpect[] =
+        "'gl_ClipDistance' : redeclaration of gl_ClipDistance after it is referenced is not "
+        "allowed";
+
+    if (hasAngle)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
+// Shader redeclares gl_CullDistance, but after it's been referenced with a constant index.
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareCullDistanceAfterReferenceConstantIndex)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+void main()
+{
+    gl_Position = aPosition;
+    gl_CullDistance[0] = 1.0;
+}
+out highp float gl_CullDistance[3];
+)";
+    constexpr char kExpect[] =
+        "'gl_CullDistance' : redeclaration of gl_CullDistance after it is referenced is not "
+        "allowed";
+
+    if (hasAngle)
+    {
+        GLint maxCullDistances = 0;
+        glGetIntegerv(GL_MAX_CULL_DISTANCES_EXT, &maxCullDistances);
+        if (maxCullDistances > 0)
+        {
+            validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+        }
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
+// Shader redeclares gl_ClipDistance, but after it's been referenced with a non-constant index.
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareClipDistanceAfterReferenceNonConstantIndex)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+void main()
+{
+    gl_Position = aPosition;
+    for (int i = 0; i < 2; ++i)
+    {
+        gl_ClipDistance[i] = 1.0;
+    }
+}
+out highp float gl_ClipDistance[3];
+)";
+    constexpr char kExpect[] =
+        "'gl_ClipDistance' : redeclaration of gl_ClipDistance after it is referenced is not "
+        "allowed";
+
+    if (hasAngle)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
+// Shader redeclares gl_CullDistance, but after it's been referenced with a non-constant index.
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareCullDistanceAfterReferenceNonConstantIndex)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+void main()
+{
+    gl_Position = aPosition;
+    for (int i = 0; i < 2; ++i)
+    {
+        gl_CullDistance[i] = 1.0;
+    }
+}
+out highp float gl_CullDistance[3];
+)";
+    constexpr char kExpect[] =
+        "'gl_CullDistance' : redeclaration of gl_CullDistance after it is referenced is not "
+        "allowed";
+
+    if (hasAngle)
+    {
+        GLint maxCullDistances = 0;
+        glGetIntegerv(GL_MAX_CULL_DISTANCES_EXT, &maxCullDistances);
+        if (maxCullDistances > 0)
+        {
+            validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+        }
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
+// Shader redeclares gl_ClipDistance, but after it's been referenced with .length().
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareClipDistanceAfterReferenceLength)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+void main()
+{
+    gl_Position = aPosition;
+    gl_Position.z = gl_ClipDistance.length();
+}
+out highp float gl_ClipDistance[3];
+)";
+    constexpr char kExpect[] =
+        "'gl_ClipDistance' : redeclaration of gl_ClipDistance after it is referenced is not "
+        "allowed";
+
+    if (hasAngle)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
+// Shader redeclares gl_CullDistance, but after it's been referenced with .length().
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareCullDistanceAfterReferenceLength)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+void main()
+{
+    gl_Position = aPosition;
+    gl_Position.z = gl_CullDistance.length();
+}
+out highp float gl_CullDistance[3];
+)";
+    constexpr char kExpect[] =
+        "'gl_CullDistance' : redeclaration of gl_CullDistance after it is referenced is not "
+        "allowed";
+
+    if (hasAngle)
+    {
+        GLint maxCullDistances = 0;
+        glGetIntegerv(GL_MAX_CULL_DISTANCES_EXT, &maxCullDistances);
+        if (maxCullDistances > 0)
+        {
+            validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+        }
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
+// Shader redeclares gl_ClipDistance twice.
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareClipDistanceTwice)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+out highp float gl_ClipDistance[3];
+out highp float gl_ClipDistance[3];
+void main()
+{
+    gl_Position = aPosition;
+    gl_ClipDistance[0] = 1.0;
+}
+)";
+    constexpr char kExpect[] = "'gl_ClipDistance' : redefinition";
+
+    if (hasAngle)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
+// Shader redeclares gl_CullDistance twice.
+TEST_P(GLSLValidationClipDistanceTest_ES3, RedeclareCullDistanceTwice)
+{
+    const bool hasExt   = IsGLExtensionEnabled("GL_EXT_clip_cull_distance");
+    const bool hasAngle = IsGLExtensionEnabled("GL_ANGLE_clip_cull_distance");
+    ANGLE_SKIP_TEST_IF(!hasExt && !hasAngle);
+
+    constexpr char kVS[] =
+        R"(in vec4 aPosition;
+out highp float gl_CullDistance[3];
+out highp float gl_CullDistance[3];
+void main()
+{
+    gl_Position = aPosition;
+    gl_CullDistance[0] = 1.0;
+}
+)";
+    constexpr char kExpect[] = "'gl_CullDistance' : redefinition";
+
+    if (hasAngle)
+    {
+        GLint maxCullDistances = 0;
+        glGetIntegerv(GL_MAX_CULL_DISTANCES_EXT, &maxCullDistances);
+        if (maxCullDistances > 0)
+        {
+            validateErrorWithExt(GL_VERTEX_SHADER, "GL_ANGLE_clip_cull_distance", kVS, kExpect);
+        }
+    }
+
+    if (hasExt)
+    {
+        validateErrorWithExt(GL_VERTEX_SHADER, "GL_EXT_clip_cull_distance", kVS, kExpect);
+    }
+}
+
 // In compute shader, redeclaring gl_ClipDistance should be denied.
 TEST_P(GLSLValidationClipDistanceTest_ES31, ComputeDeclareClipDistance)
 {