[OPT] prevent private_to_local_pass optimizing double pointer

[heroseh]

Fixes #6156

before this fix the pass will optimize the following code:

  %v = OpVariable %_ptr_Private_uint Private %uint_0
%load_thread_local = OpFunction %void None %function_type__1561_
 %37 = OpLabel
 %31 = OpVariable %_ptr_Function__ptr_Private_uint Function
 %32 = OpVariable %_ptr_Function_uint Function
 %33 = OpVariable %_ptr_Function_uint Function
       OpStore %31 %v
 %34 = OpLoad %_ptr_Private_uint %31
 %35 = OpLoad %uint %34
       OpStore %32 %35
 %36 = OpLoad %uint %v
       OpStore %33 %36
       OpReturn
       OpFunctionEnd

to this:

%load_thread_local = OpFunction %void None %function_type__1561_
 %37 = OpLabel
  %v = OpVariable %_ptr_Function_uint Function %uint_0
 %31 = OpVariable %_ptr_Function__ptr_Private_uint Function
 %32 = OpVariable %_ptr_Function_uint Function
 %33 = OpVariable %_ptr_Function_uint Function
       OpStore %31 %v
       OpStore %32 %uint_0
       OpStore %33 %uint_0
       OpReturn
       OpFunctionEnd

resulting in the following error:

error: line 81: OpStore Pointer <id> '31[%31]'s type does not match Object <id> '47[%v]'s type.
  OpStore %31 %v

private_to_local_pass does not update the storage class of the double pointer %31 correctly. It currently doesn't have enough context to tell if %31 is later loaded from and used to store with. For now, just prevent the optimization if the address of the private variable is used as the object operand of the OpStore instruction.

with this commit, the spirv code is optimized to this:

%v = OpVariable %_ptr_Private_uint Private %uint_0
%load_thread_local = OpFunction %void None %function_type__1561_
         %37 = OpLabel
         %31 = OpVariable %_ptr_Function__ptr_Private_uint Function
         %32 = OpVariable %_ptr_Function_uint Function
         %33 = OpVariable %_ptr_Function_uint Function
               OpStore %31 %v
         %35 = OpLoad %uint %v
               OpStore %32 %35
         %36 = OpLoad %uint %v
               OpStore %33 %36
               OpReturn
               OpFunctionEnd

[s-perron]

The changes to the code look good. It just needs a test. Here is an example you can follow.

https://github.com/KhronosGroup/SPIRV-Tools/blob/main/test%2Fopt%2Fprivate_to_local_test.cpp#L176

[heroseh]

I don't know why the tests failed with the previous code. Before when I made the test, I locally assembled the binary with spirv-as and done an spirv-opt & spirv-val over it but i guess i had to configured the tests to be more aggressive or something?
Anyway, I have changed them to reflect the example you linked to initially and googletest suite locally succeeds. Please let me know if anything is incorrect about it. Thanks!

[s-perron]

The test looks good now. I think you were doing a Match test with not checks in the source. I think that will fail.