HLSL legalization for isomorphic function parameter #2535
Description
It would be great if HLSL legalization handled function parameter passing where the argument is actually isomorphic to the parameter but their types are not the same.
For the following HLSL code,
struct R {
int a;
void incr() { ++a; }
};
void decr(inout R b) {
b.a--;
}
RWStructuredBuffer<R> rwsb;
void main() {
rwsb[0].incr();
decr(rwsb[0]);
}
DXC generates the following SPIR-V code for calling rwsb[0].incr(); and decr(rwsb[0]);
OpMemberDecorate %R 0 Offset 0
...
%R = OpTypeStruct %int
%R_0 = OpTypeStruct %int
%_ptr_Function_R_0 = OpTypePointer Function %R_0
%_ptr_Uniform_R = OpTypePointer Uniform %R
%rwsb = OpVariable %_ptr_Uniform_type_RWStructuredBuffer_R Uniform
...
%temp_var_R = OpVariable %_ptr_Function_R_0 Function
%param_var_b = OpVariable %_ptr_Function_R_0 Function
%26 = OpAccessChain %_ptr_Uniform_R %rwsb %int_0 %uint_0
%27 = OpLoad %R %26
%28 = OpCompositeExtract %int %27 0
%29 = OpCompositeConstruct %R_0 %28
OpStore %temp_var_R %29
%30 = OpFunctionCall %void %R_incr %temp_var_R
%32 = OpLoad %R_0 %temp_var_R
%33 = OpCompositeExtract %int %32 0
%34 = OpCompositeConstruct %R %33
OpStore %26 %34
%35 = OpAccessChain %_ptr_Uniform_R %rwsb %int_0 %uint_0
%36 = OpLoad %R %35
%37 = OpCompositeExtract %int %36 0
%38 = OpCompositeConstruct %R_0 %37
OpStore %param_var_b %38
%39 = OpFunctionCall %void %decr %param_var_b
%41 = OpLoad %R_0 %param_var_b
%42 = OpCompositeExtract %int %41 0
%43 = OpCompositeConstruct %R %42
OpStore %35 %43
After fixing #2430, the reason why we cannot directly pass
%26 = OpAccessChain %_ptr_Uniform_R %rwsb %int_0 %uint_0to%R_incr%35 = OpAccessChain %_ptr_Uniform_R %rwsb %int_0 %uint_0to%decr
because%Rand%R_0are different types.
It would be nice if HLSL legalization checked isomorphism between the parameter type and the argument type and handled it.
We need two steps for this:
- spirv-val allows a function argument that is different from the parameter type but they are isomorphic when
--relax-logical-pointeroption is enabled. - spirv-opt HLSL legalization handles it.
test.txt is the full SPIR-V code for the HLSL code.