Merge pull request #1309 from billhollings/fix-memoryless-load-store

In a renderpass, don't load or store memoryless attachments.

Docs/Whats_New.md

@@ -19,7 +19,9 @@ MoltenVK 1.1.3
 Released TBD
 
 - Add support for `HDR10` colorspace via `VK_COLOR_SPACE_HDR10_HLG_EXT` and `VK_COLOR_SPACE_HDR10_ST2084_EXT`.
-- Always explicitly set `CAMetalLayer` colorspace property based on _Vulkan_ parameters, and don't rely on _Metal_ default values.
+- Always explicitly set `CAMetalLayer` colorspace property based on _Vulkan_ parameters, 
+  and don't rely on _Metal_ default values.
+- Avoid use of _Metal_ renderpass load and store actions on memoryless attachments.
 - Remove project qualifiers from references to `SPIRV-Cross` header files.
 - Add `MVKConfiguration::apiVersionToAdvertise` and `MVK_CONFIG_API_VERSION_TO_ADVERTISE` 
   env var to configure **MoltenVK** to advertise a particular _Vulkan_ version.

MoltenVK/MoltenVK/GPUObjects/MVKRenderPass.mm

@@ -600,21 +600,21 @@ bool MVKRenderPassAttachment::populateMTLRenderPassAttachmentDescriptor(MTLRende
                                                                         bool hasResolveAttachment,
                                                                         bool isStencil,
                                                                         bool loadOverride) {
-
+    // Only allow clearing of entire attachment if we're actually
-    bool willClear = false;		// Assume the attachment won't be cleared
+	// rendering to the entire attachment AND we're in the first subpass.
-
+	MTLLoadAction mtlLA;
-    // Only allow clearing of entire attachment if we're actually rendering to the entire
+	if (loadOverride || !isRenderingEntireAttachment || !isFirstUseOfAttachment(subpass)) {
-    // attachment AND we're in the first subpass.
+		mtlLA = MTLLoadActionLoad;
-    if ( loadOverride && !isMemorylessAttachment ) {
-        mtlAttDesc.loadAction = MTLLoadActionLoad;
-    } else if ( isMemorylessAttachment || (isRenderingEntireAttachment && isFirstUseOfAttachment(subpass)) ) {
-        VkAttachmentLoadOp loadOp = isStencil ? _info.stencilLoadOp : _info.loadOp;
-        mtlAttDesc.loadAction = mvkMTLLoadActionFromVkAttachmentLoadOp(loadOp);
-        willClear = (loadOp == VK_ATTACHMENT_LOAD_OP_CLEAR);
     } else {
-        mtlAttDesc.loadAction = MTLLoadActionLoad;
+        VkAttachmentLoadOp loadOp = isStencil ? _info.stencilLoadOp : _info.loadOp;
+		mtlLA = mvkMTLLoadActionFromVkAttachmentLoadOp(loadOp);
     }
 
+	// Memoryless can be cleared, but can't be loaded, so force load to don't care.
+	if (isMemorylessAttachment && mtlLA == MTLLoadActionLoad) { mtlLA = MTLLoadActionDontCare; }
+
+	mtlAttDesc.loadAction = mtlLA;
+
     // If the device supports late-specified store actions, we'll use those, and then set them later.
     // That way, if we wind up doing a tessellated draw, we can set the store action to store then,
     // and then when the render pass actually ends, we can use the true store action.
@@ -623,7 +623,7 @@ bool MVKRenderPassAttachment::populateMTLRenderPassAttachmentDescriptor(MTLRende
     } else {
         mtlAttDesc.storeAction = getMTLStoreAction(subpass, isRenderingEntireAttachment, isMemorylessAttachment, hasResolveAttachment, isStencil, false);
     }
-    return willClear;
+    return (mtlLA == MTLLoadActionClear);
 }
 
 void MVKRenderPassAttachment::encodeStoreAction(MVKCommandEncoder* cmdEncoder,
@@ -687,19 +687,21 @@ MTLStoreAction MVKRenderPassAttachment::getMTLStoreAction(MVKRenderSubpass* subp
 														  bool isStencil,
 														  bool storeOverride) {
     // If a resolve attachment exists, this attachment must resolve once complete.
-    // Otherwise only allow the attachment to be discarded if we're actually rendering
-    // to the entire attachment and we're in the last subpass.
     if (hasResolveAttachment && !_renderPass->getDevice()->_pMetalFeatures->combinedStoreResolveAction) {
         return MTLStoreActionMultisampleResolve;
     }
-    if ( storeOverride && !isMemorylessAttachment ) {
+	// Memoryless can't be stored.
-        return hasResolveAttachment ? MTLStoreActionStoreAndMultisampleResolve : MTLStoreActionStore;
+	if (isMemorylessAttachment) {
-    }
+		return hasResolveAttachment ? MTLStoreActionMultisampleResolve : MTLStoreActionDontCare;
-    if ( isMemorylessAttachment || (isRenderingEntireAttachment && isLastUseOfAttachment(subpass)) ) {
+	}
-        VkAttachmentStoreOp storeOp = isStencil ? _info.stencilStoreOp : _info.storeOp;
+
-        return mvkMTLStoreActionFromVkAttachmentStoreOp(storeOp, hasResolveAttachment);
+	// Only allow the attachment to be discarded if we're actually
-    }
+	// rendering to the entire attachment and we're in the last subpass.
-    return hasResolveAttachment ? MTLStoreActionStoreAndMultisampleResolve : MTLStoreActionStore;
+	if (storeOverride || !isRenderingEntireAttachment || !isLastUseOfAttachment(subpass)) {
+		return hasResolveAttachment ? MTLStoreActionStoreAndMultisampleResolve : MTLStoreActionStore;
+	}
+	VkAttachmentStoreOp storeOp = isStencil ? _info.stencilStoreOp : _info.storeOp;
+	return mvkMTLStoreActionFromVkAttachmentStoreOp(storeOp, hasResolveAttachment);
 }
 
 bool MVKRenderPassAttachment::shouldUseClearAttachment(MVKRenderSubpass* subpass) {

MoltenVK/MoltenVK/Vulkan/mvk_datatypes.mm

@@ -734,10 +734,9 @@ MVK_PUBLIC_SYMBOL MTLBarrierScope mvkMTLBarrierScopeFromVkAccessFlags(VkAccessFl
 
 MVK_PUBLIC_SYMBOL MTLStorageMode mvkMTLStorageModeFromVkMemoryPropertyFlags(VkMemoryPropertyFlags vkFlags) {
 
-	// If not visible to the host: Private
+	// If not visible to the host, use Private, or Memoryless if available and lazily allocated.
 	if ( !mvkAreAllFlagsEnabled(vkFlags, VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT) ) {
 #if MVK_APPLE_SILICON
-		// iOS: If lazily allocated, Memoryless
 		if (mvkAreAllFlagsEnabled(vkFlags, VK_MEMORY_PROPERTY_LAZILY_ALLOCATED_BIT)) {
 			return MTLStorageModeMemoryless;
 		}