[vulkan] Disable shader optimization to avoid Validation Errors (pytorch#69331)

Summary:
Pull Request resolved: pytorch#69331

 ---

## Context

When the optimization flag is turned on, some SPIR-V modules produced from the Vulkan compute shaders were invalid. The Vulkan Validation layer raises the following error for these modules:

```
[ UNASSIGNED-CoreValidation-Shader-InconsistentSpirv ] Object: VK_NULL_HANDLE (Type = 0) | SPIR-V module not valid: Header block 52[%52] is contained in the loop construct headed by 44[%44], but it's merge block 47[%47] is not
%52 = OpLabel
```

Turning off the optimization flag, the SPIR-V modules produced no longer reports these errors in the Validation layer.

## Changes

Turns off optimization when generating SPIR-V modules to ensure correctness of the modules.

**Note that disabling SPIR-V optimization did not regress inference latency for the several models I tested**.

Test Plan: Imported from OSS

Reviewed By: beback4u

Differential Revision: D32840910

Pulled By: SS-JIA

fbshipit-source-id: 7ccb5691fd0e2d11b9c8c28ad7b83906e8163699

Author: SS-JIA

aten/src/ATen/gen_vulkan_spv.py

@@ -43,7 +43,7 @@ def genCppH(hFilePath, cppFilePath, srcDirPath, glslcPath, tmpDirPath, env):
         print("spvPath {}".format(spvPath))
 
         cmd = [
-            glslcPath, "-fshader-stage=compute", "-Os",
+            glslcPath, "-fshader-stage=compute",
             srcPath, "-o", spvPath,
             "--target-env=vulkan1.0",
             "-Werror"

aten/src/ATen/native/vulkan/api/Shader.cpp

@@ -77,10 +77,8 @@ struct Shader::Factory::Compiler final {
     options.SetWarningsAsErrors();
   #ifdef DEBUG
     options.SetGenerateDebugInfo();
-    options.SetOptimizationLevel(shaderc_optimization_level_zero);
-  #else
-    options.SetOptimizationLevel(shaderc_optimization_level_performance);
   #endif /* DEBUG */
+    options.SetOptimizationLevel(shaderc_optimization_level_zero);
   }
 
   std::vector<uint32_t> compile(const char* const source) const {