Vk: add an execution-only pipelineBarrier() overload.

Useful for WAR barriers. I also *finally* get why is it called a
pipeline barrier and not a memory barrier.

src/Magnum/Vk/CommandBuffer.h

@@ -358,7 +358,7 @@ class MAGNUM_VK_EXPORT CommandBuffer {
         #endif
 
         /**
-         * @brief Insert a memory dependency
+         * @brief Insert an execution barrier with optional memory dependencies
          * @param sourceStages          Source stages. Has to contain at least
          *      one stage.
          * @param destinationStages     Destination stages. Has to contain at
@@ -395,6 +395,18 @@ class MAGNUM_VK_EXPORT CommandBuffer {
         /** @overload */
         CommandBuffer& pipelineBarrier(PipelineStages sourceStages, PipelineStages destinationStages, std::initializer_list<MemoryBarrier> memoryBarriers, std::initializer_list<BufferMemoryBarrier> bufferMemoryBarriers, std::initializer_list<ImageMemoryBarrier> imageMemoryBarriers, DependencyFlags dependencyFlags = {});
 
+        /**
+         * @brief Insert an execution barrier without memory dependencies
+         * @return Reference to self (for method chaining)
+         *
+         * Equivalent to calling @ref pipelineBarrier(PipelineStages, PipelineStages, Containers::ArrayView<const MemoryBarrier>, Containers::ArrayView<const BufferMemoryBarrier>, Containers::ArrayView<const ImageMemoryBarrier>, DependencyFlags)
+         * with empty @p memoryBarriers, @p bufferBarriers and
+         * @p imageBarriers. Useful when an execution barrier is enough, for
+         * example when you need reads from one stage to finish before another
+         * stage starts writing to the same location.
+         */
+        CommandBuffer& pipelineBarrier(PipelineStages sourceStages, PipelineStages destinationStages, DependencyFlags dependencyFlags = {});
+
         /**
          * @brief Insert a global memory dependency
          * @return Reference to self (for method chaining)

src/Magnum/Vk/Pipeline.cpp

@@ -101,6 +101,10 @@ CommandBuffer& CommandBuffer::pipelineBarrier(const PipelineStages sourceStages,
     return pipelineBarrier(sourceStages, destinationStages, Containers::arrayView(memoryBarriers), Containers::arrayView(bufferMemoryBarriers), Containers::arrayView(imageMemoryBarriers), dependencyFlags);
 }
 
+CommandBuffer& CommandBuffer::pipelineBarrier(const PipelineStages sourceStages, const PipelineStages destinationStages, const DependencyFlags dependencyFlags) {
+    return pipelineBarrier(sourceStages, destinationStages, {}, {}, {}, dependencyFlags);
+}
+
 CommandBuffer& CommandBuffer::pipelineBarrier(const PipelineStages sourceStages, const PipelineStages destinationStages, const Containers::ArrayView<const MemoryBarrier> memoryBarriers, const DependencyFlags dependencyFlags) {
     return pipelineBarrier(sourceStages, destinationStages, memoryBarriers, {}, {}, dependencyFlags);
 }

src/Magnum/Vk/Test/PipelineVkTest.cpp

@@ -38,16 +38,18 @@ struct PipelineVkTest: VulkanTester {
     explicit PipelineVkTest();
 
     void pipelineBarrier();
-    void pipelineBarrierGeneral();
-    void pipelineBarrierBuffer();
-    void pipelineBarrierImage();
+    void pipelineBarrierExecutionOnly();
+    void pipelineBarrierGlobalMemory();
+    void pipelineBarrierBufferMemory();
+    void pipelineBarrierImageMemory();
 };
 
 PipelineVkTest::PipelineVkTest() {
     addTests({&PipelineVkTest::pipelineBarrier,
-              &PipelineVkTest::pipelineBarrierGeneral,
-              &PipelineVkTest::pipelineBarrierBuffer,
-              &PipelineVkTest::pipelineBarrierImage});
+              &PipelineVkTest::pipelineBarrierExecutionOnly,
+              &PipelineVkTest::pipelineBarrierGlobalMemory,
+              &PipelineVkTest::pipelineBarrierBufferMemory,
+              &PipelineVkTest::pipelineBarrierImageMemory});
 }
 
 void PipelineVkTest::pipelineBarrier() {
@@ -79,7 +81,22 @@ void PipelineVkTest::pipelineBarrier() {
     CORRADE_VERIFY(true);
 }
 
-void PipelineVkTest::pipelineBarrierGeneral() {
+void PipelineVkTest::pipelineBarrierExecutionOnly() {
+    CommandPool pool{device(), CommandPoolCreateInfo{
+        device().properties().pickQueueFamily(QueueFlag::Graphics)}};
+
+    /* A subset of the above, just to test the convenience overloads */
+
+    pool.allocate()
+        .begin()
+        .pipelineBarrier(PipelineStage::Transfer, PipelineStage::Host)
+        .end();
+
+    /* Does not do anything visible, so just test that it didn't blow up */
+    CORRADE_VERIFY(true);
+}
+
+void PipelineVkTest::pipelineBarrierGlobalMemory() {
     CommandPool pool{device(), CommandPoolCreateInfo{
         device().properties().pickQueueFamily(QueueFlag::Graphics)}};
 
@@ -96,7 +113,7 @@ void PipelineVkTest::pipelineBarrierGeneral() {
     CORRADE_VERIFY(true);
 }
 
-void PipelineVkTest::pipelineBarrierBuffer() {
+void PipelineVkTest::pipelineBarrierBufferMemory() {
     CommandPool pool{device(), CommandPoolCreateInfo{
         device().properties().pickQueueFamily(QueueFlag::Graphics)}};
 
@@ -115,7 +132,7 @@ void PipelineVkTest::pipelineBarrierBuffer() {
     CORRADE_VERIFY(true);
 }
 
-void PipelineVkTest::pipelineBarrierImage() {
+void PipelineVkTest::pipelineBarrierImageMemory() {
     CommandPool pool{device(), CommandPoolCreateInfo{
         device().properties().pickQueueFamily(QueueFlag::Graphics)}};