Not pretty, but with this, you can switch MSAA level at runtime.

Common/Data/Convert/SmallDataConvert.h

@@ -21,7 +21,7 @@ extern const float one_over_255_x4[4];
 extern const float exactly_255_x4[4];
 
 // Utilities useful for filling in std140-layout uniform buffers, and similar.
-// NEON intrinsics: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0491f/BABDCGGF.html
+// NEON intrinsics: https://developer.arm.com/documentation/den0018/a/NEON-Intrinsics?lang=en
 
 // LSBs in f[0], etc.
 inline void Uint8x4ToFloat4(float f[4], uint32_t u) {

Common/GPU/Vulkan/VulkanQueueRunner.cpp

@@ -1327,10 +1327,8 @@ void VulkanQueueRunner::PerformRenderPass(const VKRStep &step, VkCommandBuffer c
 				VkSampleCountFlagBits fbSampleCount = step.render.framebuffer ? step.render.framebuffer->sampleCount : VK_SAMPLE_COUNT_1_BIT;
 
 				if (RenderPassTypeHasMultisample(rpType) && fbSampleCount != graphicsPipeline->SampleCount()) {
-					// Sample count might have started mismatching if the user changed multisampling mode. Let's get rid of all variants
-					// and start over.
-					// (We could avoid this if sample count was baked into the rpType, but I don't want that to grow too big).
-					graphicsPipeline->DestroyAllVariants(vulkan_);
+					// Shouldn't happen, pipeline invalidation after render resized should have taken care of this.
+					_assert_(false);
 				}
 
 				if (!graphicsPipeline->pipeline[(size_t)rpType]) {

Common/GPU/Vulkan/VulkanRenderManager.cpp

@@ -130,10 +130,13 @@ bool VKRGraphicsPipeline::Create(VulkanContext *vulkan, VkRenderPass compatibleR
 	return success;
 }
 
-void VKRGraphicsPipeline::DestroyAllVariants(VulkanContext *vulkan) {
+void VKRGraphicsPipeline::DestroyVariants(VulkanContext *vulkan, bool msaaOnly) {
 	for (size_t i = 0; i < (size_t)RenderPassType::TYPE_COUNT; i++) {
 		if (!this->pipeline[i])
 			continue;
+		if (msaaOnly && (i & (int)RenderPassType::MULTISAMPLE) == 0)
+			continue;
+
 		VkPipeline pipeline = this->pipeline[i]->BlockUntilReady();
 		// pipeline can be nullptr here, if it failed to compile before.
 		if (pipeline) {
@@ -145,7 +148,7 @@ void VKRGraphicsPipeline::DestroyAllVariants(VulkanContext *vulkan) {
 }
 
 void VKRGraphicsPipeline::QueueForDeletion(VulkanContext *vulkan) {
-	DestroyAllVariants(vulkan);
+	DestroyVariants(vulkan, false);
 	vulkan->Delete().QueueCallback([](void *p) {
 		VKRGraphicsPipeline *pipeline = (VKRGraphicsPipeline *)p;
 		delete pipeline;

Common/GPU/Vulkan/VulkanRenderManager.h

@@ -124,7 +124,7 @@ struct VKRGraphicsPipeline {
 
 	bool Create(VulkanContext *vulkan, VkRenderPass compatibleRenderPass, RenderPassType rpType, VkSampleCountFlagBits sampleCount);
 
-	void DestroyAllVariants(VulkanContext *vulkan);
+	void DestroyVariants(VulkanContext *vulkan, bool msaaOnly);
 
 	// This deletes the whole VKRGraphicsPipeline, you must remove your last pointer to it when doing this.
 	void QueueForDeletion(VulkanContext *vulkan);
@@ -458,6 +458,8 @@ public:
 		return outOfDateFrames_ > VulkanContext::MAX_INFLIGHT_FRAMES;
 	}
 
+	void Invalidate(InvalidationFlags flags);
+
 	void ResetStats();
 
 private:

Common/GPU/Vulkan/thin3d_vulkan.cpp

@@ -242,7 +242,7 @@ bool VKShaderModule::Compile(VulkanContext *vulkan, ShaderLanguage language, con
 #endif
 
 	VkShaderModule shaderModule = VK_NULL_HANDLE;
-	if (vulkan->CreateShaderModule(spirv, &shaderModule, vkstage_ == VK_SHADER_STAGE_VERTEX_BIT ? "thin3d_vs" : "thin3d_fs")) {
+	if (vulkan->CreateShaderModule(spirv, &shaderModule, tag_.c_str())) {
 		module_ = Promise<VkShaderModule>::AlreadyDone(shaderModule);
 		ok_ = true;
 	} else {

GPU/Common/FramebufferManagerCommon.cpp

@@ -2878,11 +2878,7 @@ static void DoRelease(T *&obj) {
 	obj = nullptr;
 }
 
-void FramebufferManagerCommon::DeviceLost() {
-	DestroyAllFBOs();
-
-	presentation_->DeviceLost();
-
+void FramebufferManagerCommon::ReleasePipelines() {
 	for (int i = 0; i < ARRAY_SIZE(reinterpretFromTo_); i++) {
 		for (int j = 0; j < ARRAY_SIZE(reinterpretFromTo_); j++) {
 			DoRelease(reinterpretFromTo_[i][j]);
@@ -2899,9 +2895,16 @@ void FramebufferManagerCommon::DeviceLost() {
 	DoRelease(draw2DPipelineDepth_);
 	DoRelease(draw2DPipeline565ToDepth_);
 	DoRelease(draw2DPipeline565ToDepthDeswizzle_);
+}
 
+void FramebufferManagerCommon::DeviceLost() {
+	DestroyAllFBOs();
+
+	presentation_->DeviceLost();
 	draw2D_.DeviceLost();
 
+	ReleasePipelines();
+
 	draw_ = nullptr;
 }
 

GPU/Common/FramebufferManagerCommon.h

@@ -443,6 +443,8 @@ public:
 		int scaleFactor,  // usually unused, except for swizzle...
 		Draw2DPipeline *pipeline, const char *tag);
 
+	void ReleasePipelines();
+
 protected:
 	virtual void ReadbackFramebufferSync(VirtualFramebuffer *vfb, int x, int y, int w, int h, RasterChannel channel);
 	// Used for when a shader is required, such as GLES.

GPU/GPUCommon.h

@@ -267,7 +267,7 @@ protected:
 	void DeviceLost() override;
 	void DeviceRestore() override;
 
-	void CheckRenderResized();
+	virtual void CheckRenderResized();
 
 	// Add additional common features dependent on other features, which may be backend-determined.
 	u32 CheckGPUFeaturesLate(u32 features) const;

GPU/Vulkan/GPU_Vulkan.cpp

@@ -465,6 +465,14 @@ void GPU_Vulkan::DestroyDeviceObjects() {
 	}
 }
 
+void GPU_Vulkan::CheckRenderResized() {
+	if (renderResized_) {
+		GPUCommon::CheckRenderResized();
+		pipelineManager_->InvalidateMSAAPipelines();
+		framebufferManager_->ReleasePipelines();
+	}
+}
+
 void GPU_Vulkan::DeviceLost() {
 	CancelReady();
 	while (!IsReady()) {

GPU/Vulkan/GPU_Vulkan.h

@@ -70,6 +70,7 @@ public:
 
 protected:
 	void FinishDeferred() override;
+	void CheckRenderResized() override;
 
 private:
 	void Flush() {

GPU/Vulkan/PipelineManagerVulkan.cpp

@@ -49,6 +49,12 @@ void PipelineManagerVulkan::Clear() {
 	pipelines_.Clear();
 }
 
+void PipelineManagerVulkan::InvalidateMSAAPipelines() {
+	pipelines_.Iterate([&](const VulkanPipelineKey &key, VulkanPipeline *value) {
+		value->pipeline->DestroyVariants(vulkan_, true);
+	});
+}
+
 void PipelineManagerVulkan::DeviceLost() {
 	Clear();
 	if (pipelineCache_ != VK_NULL_HANDLE)

GPU/Vulkan/PipelineManagerVulkan.h

@@ -88,6 +88,8 @@ public:
 	void DeviceLost();
 	void DeviceRestore(VulkanContext *vulkan);
 
+	void InvalidateMSAAPipelines();
+
 	std::string DebugGetObjectString(std::string id, DebugShaderType type, DebugShaderStringType stringType);
 	std::vector<std::string> DebugGetObjectIDs(DebugShaderType type);