Compiler warning: Wsometimes-uninitialized

[jordanmontt]

If one compiles the vm with the warning Wsometimes-uninitialized, we have one case of a sometimes uninitialized variable. This happens in the method StackToRegisterMappingCogit>>#genSpecialSelectorArithmetic in the line 20, for the result temp variable:

genSpecialSelectorArithmetic
"More code ......."	

		 primDescriptor opcode caseOf: {
			[AddRR]	-> [result := rcvrInt + argInt].
			[SubRR]	-> [result := rcvrInt - argInt].
			[AndRR]	-> [result := rcvrInt bitAnd: argInt].
			[OrRR]	-> [result := rcvrInt bitOr: argInt] }.
		(objectMemory isIntegerValue: result) ifTrue:
			["Must annotate the bytecode for correct pc mapping."
			^self ssPop: 2; ssPushAnnotatedConstant: (objectMemory integerObjectOf: result)].

" More code ...."

Indeed, the variable result, if non of the cases of the caseOf: is met, then is left uninitialized. But, if we look at the implementation of Object>>#caseOf:, when non of the cases is satisfied, an error is raised. So actually the variable is NEVER uninitialized, because when that happens we have an error.

This is translated into C as the following:

switch ((primDescriptor->opcode)) {
			case AddRR:
			{
				result = rcvrInt + argInt;
			}
			break;
			case SubRR:
			{
				result = rcvrInt - argInt;
			}
			break;
			case AndRR:
			{
				result = rcvrInt & argInt;
			}
			break;
			case OrRR:
			{
				result = rcvrInt | argInt;
			}
			break;
			default:
			error("Case not found and no otherwise clause");
			
		}

As one can see, indeed if non of the cases is satisfied, the function error is called. But, the C compiler does not know that and it produced the warning.

Possible solutions
We could refactor the method to always initialize the variable, but I don't know if that is a good idea since is good to have an error.

We could annotate the C code to say to the compiler to not produce the warning ONLY for that variable in that method.