GL: Fix `invariant gl_FragColor;` + draw buffers

When GL_EXT_draw_buffers is enabled, gl_FragColor is replaced by
gl_FragData.  If it was globally qualified as `invariant`, the relevant
transformation did not handle it.

Bug: chromium:517575864
Change-Id: I3ec2a6629940a69070e5327abd8ce37c55d0efcd
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/7883926
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>

src/compiler/translator/ir/src/transform/broadcast_fragcolor.rs

diff --git a/src/compiler/translator/ir/src/transform/broadcast_fragcolor.rs b/src/compiler/translator/ir/src/transform/broadcast_fragcolor.rs
index 517946c..0c40534 100644
--- a/src/compiler/translator/ir/src/transform/broadcast_fragcolor.rs
+++ b/src/compiler/translator/ir/src/transform/broadcast_fragcolor.rs
@@ -49,7 +49,8 @@
         let replacement = ir.meta.get_variable_mut(original_id);
         replacement.name = Name::new_temp(name);
         replacement.built_in = None;
-        debug_assert!(replacement.decorations.decorations.is_empty());
+        // The built-in might have decorations such as Invariant
+        let decorations = std::mem::replace(&mut replacement.decorations, Decorations::new_none());
         debug_assert!(replacement.scope == VariableScope::Global);
         debug_assert!(!replacement.is_const);
 
@@ -66,7 +67,9 @@
         let type_id = ir.meta.get_array_type_id(type_id, array_size);
         let (arrayed_built_in_id, arrayed_built_in) =
             ir.meta.declare_built_in_variable(type_id, precision, broadcast_to);
-        ir.meta.get_variable_mut(arrayed_built_in_id).is_static_use = true;
+        let new_built_in = ir.meta.get_variable_mut(arrayed_built_in_id);
+        new_built_in.is_static_use = true;
+        new_built_in.decorations = decorations;
 
         // Since the variable ID is unchanged, the IR does not need further modification.  The
         // transformation only needs to replicate the value of the global variable in each element

src/compiler/translator/tree_ops/EmulateGLFragColorBroadcast.cpp

diff --git a/src/compiler/translator/tree_ops/EmulateGLFragColorBroadcast.cpp b/src/compiler/translator/tree_ops/EmulateGLFragColorBroadcast.cpp
index 99532a4..3100952 100644
--- a/src/compiler/translator/tree_ops/EmulateGLFragColorBroadcast.cpp
+++ b/src/compiler/translator/tree_ops/EmulateGLFragColorBroadcast.cpp
@@ -51,6 +51,8 @@
     bool isGLSecondaryFragColorUsed() const { return mGLSecondaryFragColorUsed; }
 
   protected:
+    bool visitGlobalQualifierDeclaration(Visit visit,
+                                         TIntermGlobalQualifierDeclaration *node) override;
     void visitSymbol(TIntermSymbol *node) override;
 
     TIntermBinary *constructGLFragDataNode(int index, bool secondary) const;
@@ -84,6 +86,31 @@
     return new TIntermBinary(EOpAssign, fragDataIndex, fragDataZero);
 }
 
+bool GLFragColorBroadcastTraverser::visitGlobalQualifierDeclaration(
+    Visit visit,
+    TIntermGlobalQualifierDeclaration *node)
+{
+    TIntermSymbol *symbol = node->getSymbol();
+    if (symbol->variable().symbolType() == SymbolType::BuiltIn)
+    {
+        if (symbol->getName() == "gl_FragColor")
+        {
+            queueReplacementWithParent(
+                node, node->getSymbol(),
+                ReferenceBuiltInVariable(kGlFragDataString, *mSymbolTable, mShaderVersion),
+                OriginalNode::IS_DROPPED);
+        }
+        else if (symbol->getName() == "gl_SecondaryFragColorEXT")
+        {
+            queueReplacementWithParent(
+                node, node->getSymbol(),
+                ReferenceBuiltInVariable(kGlSecondaryFragDataString, *mSymbolTable, mShaderVersion),
+                OriginalNode::IS_DROPPED);
+        }
+    }
+    return false;
+}
+
 void GLFragColorBroadcastTraverser::visitSymbol(TIntermSymbol *node)
 {
     if (node->variable().symbolType() == SymbolType::BuiltIn)

src/tests/angle_end2end_tests_expectations.txt

diff --git a/src/tests/angle_end2end_tests_expectations.txt b/src/tests/angle_end2end_tests_expectations.txt
index 446507c..9f95376 100644
--- a/src/tests/angle_end2end_tests_expectations.txt
+++ b/src/tests/angle_end2end_tests_expectations.txt
@@ -497,6 +497,8 @@
 494341324 MAC OPENGL : MipmapTestES3.MismatchingLevelFormats/* = SKIP
 496604559 MAC METAL : RobustResourceInitTestES3.DrawThenInvalidateThenVerifyDepthStencil/* = SKIP
 515709506 MAC METAL : DrawBaseVertexBaseInstanceTest_ES3.BaseInstanceSmallDivisorClientMemory/* = SKIP
+518849408 MAC OPENGL : GLSLTest.EmulateGLFragColorBroadcastInvariantFragColor/* = SKIP
+518849408 MAC OPENGL : GLSLTest.EmulateGLFragColorBroadcastInvariantFragColorUnused/* = SKIP
 
 // The workaround is not intended to be enabled in this configuration so
 // skip it as the failure is likely a driver bug.

src/tests/gl_tests/GLSLTest.cpp

diff --git a/src/tests/gl_tests/GLSLTest.cpp b/src/tests/gl_tests/GLSLTest.cpp
index 519ac59..79ed94c 100644
--- a/src/tests/gl_tests/GLSLTest.cpp
+++ b/src/tests/gl_tests/GLSLTest.cpp
@@ -24164,6 +24164,40 @@
     // (Note: 565 with no alpha, glReadPixels will pad alpha to 255).
     EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::white);
 }
+
+// Make sure gl_FragColor can be marked invariant in presence of GL_EXT_draw_buffers.
+TEST_P(GLSLTest, EmulateGLFragColorBroadcastInvariantFragColor)
+{
+    ANGLE_SKIP_TEST_IF(!EnsureGLExtensionEnabled("GL_EXT_draw_buffers"));
+
+    constexpr char kFS[] = R"(#extension GL_EXT_draw_buffers : require
+        invariant gl_FragColor;
+        void main() {
+            gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
+        }
+    )";
+
+    ANGLE_GL_PROGRAM(program, essl1_shaders::vs::Simple(), kFS);
+    drawQuad(program, essl3_shaders::PositionAttrib(), 0.5f);
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::red);
+}
+
+// Make sure gl_FragColor can be marked invariant in presence of GL_EXT_draw_buffers, even if
+// gl_FragColor is unused.
+TEST_P(GLSLTest, EmulateGLFragColorBroadcastInvariantFragColorUnused)
+{
+    ANGLE_SKIP_TEST_IF(!EnsureGLExtensionEnabled("GL_EXT_draw_buffers"));
+
+    constexpr char kFS[] = R"(#extension GL_EXT_draw_buffers : require
+        invariant gl_FragColor;
+        void main() {
+            // gl_FragColor is unused
+        }
+    )";
+
+    // Verify compilation only, as output is not written to.
+    ANGLE_GL_PROGRAM(program, essl1_shaders::vs::Simple(), kFS);
+}
 }  // anonymous namespace
 
 ANGLE_INSTANTIATE_TEST_ES2_AND_ES3_AND_ES31_AND_ES32(