Always scalarize mat and vec constructor arguments.

include/platform/FrontendFeatures.h

@@ -44,6 +44,11 @@ struct FrontendFeatures : angle::FeatureSetBase
         "On Windows Intel OpenGL drivers TexImage sometimes seems to interact "
         "with the Framebuffer",
         &members};
+
+    angle::Feature scalarizeVecAndMatConstructorArgs = {
+        "scalarize_vec_and_mat_constructor_args", angle::FeatureCategory::FrontendWorkarounds,
+        "Always rewrite vec/mat constructors to be consistent", &members,
+        "http://crbug.com/398694"};
 };
 
 inline FrontendFeatures::FrontendFeatures()  = default;

src/libANGLE/Display.cpp

@@ -1350,6 +1350,7 @@ void Display::initializeFrontendFeatures()
 {
     // Enable on all Impls
     mFrontendFeatures.loseContextOnOutOfMemory.enabled = true;
+    mFrontendFeatures.scalarizeVecAndMatConstructorArgs.enabled = true;
 
     mImplementation->initializeFrontendFeatures(&mFrontendFeatures);
 

src/libANGLE/Shader.cpp

@@ -22,6 +22,7 @@
 #include "libANGLE/ResourceManager.h"
 #include "libANGLE/renderer/GLImplFactory.h"
 #include "libANGLE/renderer/ShaderImpl.h"
+#include "platform/FrontendFeatures.h"
 
 namespace gl
 {
@@ -342,6 +343,11 @@ void Shader::compile(const Context *context)
         options |= SH_VALIDATE_LOOP_INDEXING;
     }
 
+    if (context->getFrontendFeatures().scalarizeVecAndMatConstructorArgs.enabled)
+    {
+        options |= SH_SCALARIZE_VEC_AND_MAT_CONSTRUCTOR_ARGS;
+    }
+
     mCurrentMaxComputeWorkGroupInvocations = context->getCaps().maxComputeWorkGroupInvocations;
 
     ASSERT(mBoundCompiler.get());