Enable blend optimizations with instanced draws

src/gpu/instanced/InstanceProcessor.cpp

Index: src/gpu/instanced/InstanceProcessor.cpp
diff --git a/src/gpu/instanced/InstanceProcessor.cpp b/src/gpu/instanced/InstanceProcessor.cpp
index 80437a110a04a6b1b971a160a27e6c951e76105d..0266d43f7f87ef1cdfb983543f102b13dc6bcf61 100644
--- a/src/gpu/instanced/InstanceProcessor.cpp
+++ b/src/gpu/instanced/InstanceProcessor.cpp
@@ -141,8 +141,7 @@ private:
 
 class GLSLInstanceProcessor::Backend {
 public:
-    static Backend* SK_WARN_UNUSED_RESULT Create(const GrGLSLProgramBuilder*, BatchInfo,
-                                                 const VertexInputs&);
+    static Backend* SK_WARN_UNUSED_RESULT Create(const GrPipeline&, BatchInfo, const VertexInputs&);
     virtual ~Backend() {}
 
     void init(GrGLSLVaryingHandler*, GrGLSLVertexBuilder*);
@@ -208,6 +207,7 @@ protected:
 };
 
 void GLSLInstanceProcessor::onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) {
+    const GrPipeline& pipeline = args.fVertBuilder->getProgramBuilder()->pipeline();
     const InstanceProcessor& ip = args.fGP.cast<InstanceProcessor>();
     GrGLSLUniformHandler* uniHandler = args.fUniformHandler;
     GrGLSLVaryingHandler* varyingHandler = args.fVaryingHandler;
@@ -247,7 +247,7 @@ void GLSLInstanceProcessor::onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) {
                        inputs.attr(Attrib::kInstanceInfo));
     }
 
-    SkAutoTDelete<Backend> backend(Backend::Create(v->getProgramBuilder(), ip.batchInfo(), inputs));
+    SkAutoTDelete<Backend> backend(Backend::Create(pipeline, ip.batchInfo(), inputs));
     backend->init(varyingHandler, v);
 
     if (hasSingleShapeType) {
@@ -339,7 +339,8 @@ void GLSLInstanceProcessor::onEmitCode(EmitArgs& args, GrGPArgs* gpArgs) {
         v->definef("OVAL_SHAPE_TYPE", "%du", (int)ShapeType::kOval);
     }
 
-    backend->emitCode(v, f, args.fOutputCoverage, args.fOutputColor);
+    backend->emitCode(v, f, pipeline.ignoresCoverage() ? nullptr : args.fOutputCoverage,
+                      args.fOutputColor);
 
     const char* localCoords = nullptr;
     if (ip.batchInfo().fUsesLocalCoords) {
@@ -516,9 +517,10 @@ void GLSLInstanceProcessor::Backend::setupInnerRRect(GrGLSLVertexBuilder* v) {
 
 void GLSLInstanceProcessor::Backend::emitCode(GrGLSLVertexBuilder* v, GrGLSLPPFragmentBuilder* f,
                                               const char* outCoverage, const char* outColor) {
+    SkASSERT(!fModifiesCoverage || outCoverage);
     this->onEmitCode(v, f, fModifiesCoverage ? outCoverage : nullptr,
                      fModifiesColor ? outColor : nullptr);
-    if (!fModifiesCoverage) {
+    if (outCoverage && !fModifiesCoverage) {
         // Even though the subclass doesn't use coverage, we are expected to assign some value.
         f->codeAppendf("%s = vec4(1);", outCoverage);
     }
@@ -1661,7 +1663,7 @@ void GLSLInstanceProcessor::BackendMultisample::acceptCoverageMask(GrGLSLPPFragm
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 GLSLInstanceProcessor::Backend*
-GLSLInstanceProcessor::Backend::Create(const GrGLSLProgramBuilder* p, BatchInfo batchInfo,
+GLSLInstanceProcessor::Backend::Create(const GrPipeline& pipeline, BatchInfo batchInfo,
                                        const VertexInputs& inputs) {
     switch (batchInfo.fAntialiasMode) {
         default:
@@ -1672,7 +1674,6 @@ GLSLInstanceProcessor::Backend::Create(const GrGLSLProgramBuilder* p, BatchInfo
             return new BackendCoverage(batchInfo, inputs);
         case AntialiasMode::kMSAA:
         case AntialiasMode::kMixedSamples: {
-            const GrPipeline& pipeline = p->pipeline();
             const GrRenderTargetPriv& rtp = pipeline.getRenderTarget()->renderTargetPriv();
             const GrGpu::MultisampleSpecs& specs = rtp.getMultisampleSpecs(pipeline.getStencil());
             return new BackendMultisample(batchInfo, inputs, specs.fEffectiveSampleCnt);