[ET-VK][ez] Fix undefined behaviour in ambiguous ParamsBuffer const…

…ructor (#7482)

## Context

I discovered this bug when trying to execute the `vulkan_compute_api_test` binary on Windows. Almost all the tests were failing, with compute shaders producing incorrect results. After bisecting the change, it turns out the culprit is #7015. The diff introduced an alternative templated constructor for `ParamsBuffer` which would initialize an empty UBO with a specified size instead of wrapping a pre-existing object.

The issue is that these constructors are ambiguous because they both are template constructors and both only accept one argument. Therefore, the original constructor would be called when certain callsites intended to call the new constructor. This results in a UBO being created with an incorrect size, and resulted in the tensor's metadata being passed incorrectly into a compute shader.

To fix, I added a dummy argument into the new constructor for disambiguation purposes. I also changed it so that it's not templated, since there's no reason for it to be templated.

Differential Revision: [D67770791](https://our.internmc.facebook.com/intern/diff/D67770791/)

ghstack-source-id: 260031108
Pull Request resolved: #7478

Co-authored-by: Stephen Jia <ssjia@meta.com>

backends/vulkan/runtime/api/containers/ParamsBuffer.h

@@ -31,8 +31,9 @@ class ParamsBuffer final {
         vulkan_buffer_(
             context_p_->adapter_ptr()->vma().create_params_buffer(block)) {}
 
-  template <typename Block>
-  ParamsBuffer(Context* context_p, const VkDeviceSize nbytes)
+  // The last bool argument, though unused, is required to disambiguate this
+  // constructor from the one above.
+  ParamsBuffer(Context* context_p, const VkDeviceSize nbytes, const bool unused)
       : context_p_(context_p),
         vulkan_buffer_(
             context_p_->adapter_ptr()->vma().create_uniform_buffer(nbytes)) {}

backends/vulkan/runtime/api/containers/Tensor.cpp

@@ -659,7 +659,7 @@ utils::GPUMemoryLayout vTensor::estimate_memory_layout() const {
 
 const vkapi::BufferBindInfo vTensor::sizes_ubo() {
   if (!uniforms_.buffer()) {
-    uniforms_ = ParamsBuffer(storage_.context_, kMaxUniformBufferSize);
+    uniforms_ = ParamsBuffer(storage_.context_, kMaxUniformBufferSize, true);
   }
   if (sizes_uniform_offset_ == kUniformOffsetUnset) {
     VK_CHECK_COND(
@@ -674,7 +674,7 @@ const vkapi::BufferBindInfo vTensor::sizes_ubo() {
 
 const vkapi::BufferBindInfo vTensor::strides_ubo() {
   if (!uniforms_.buffer()) {
-    uniforms_ = ParamsBuffer(storage_.context_, kMaxUniformBufferSize);
+    uniforms_ = ParamsBuffer(storage_.context_, kMaxUniformBufferSize, true);
   }
   if (unsqueezed_strides_offset_ == kUniformOffsetUnset) {
     VK_CHECK_COND(
@@ -691,7 +691,7 @@ const vkapi::BufferBindInfo vTensor::strides_ubo() {
 
 const vkapi::BufferBindInfo vTensor::logical_limits_ubo() {
   if (!uniforms_.buffer()) {
-    uniforms_ = ParamsBuffer(storage_.context_, kMaxUniformBufferSize);
+    uniforms_ = ParamsBuffer(storage_.context_, kMaxUniformBufferSize, true);
   }
   if (logical_limits_uniform_offset_ == kUniformOffsetUnset) {
     VK_CHECK_COND(
@@ -707,7 +707,7 @@ const vkapi::BufferBindInfo vTensor::logical_limits_ubo() {
 
 const vkapi::BufferBindInfo vTensor::numel_ubo() {
   if (!uniforms_.buffer()) {
-    uniforms_ = ParamsBuffer(storage_.context_, kMaxUniformBufferSize);
+    uniforms_ = ParamsBuffer(storage_.context_, kMaxUniformBufferSize, true);
   }
   if (numel_uniform_offset_ == kUniformOffsetUnset) {
     VK_CHECK_COND(