[PATCH] D35994: Debug info for variables whose type is shrinked to bool

[Nikola Prica via Phabricator via llvm-commits]

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>> 
>> 
>>   val * (ValOther - ValInit) + ValInit:
> 
> If we are doing this expression, there should be an assertion in the code that `ValInit < ValOther`.

I have tested this for edge cases such as both negative values, LONG_MAX, LONG_INT etc and there was no problem for this values. Only flaw for this is ugly long DW_AT_location expression for long values.

>>    DW_OP_deref DW_OP_constu <ValMinus>
>>   DW_OP_mul DW_OP_constu <ValInit> DW_OP_plus DW_OP_stack_value
> 
> Why does `Val` need to be dereferenced?

DW_OP_deref needs to be used because we have address of new variable on stack, not its value.

> Apart from the DW_OP_deref, this seems very good, I'm slightly worried about the assumption that the init value will always be the smaller one.
>  What happens if any of the two values is negative (because of the typeless DWARF <5 expression stack — not sure if this will be a problem).

For dwarf versions lower than 4 gdb reads value of DW_AT_location expression as address giving message "Cannot access memory at address 0x1e". This may be a problem but it is still better than optimized-out?


https://reviews.llvm.org/D35994