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

[Adrian Prantl via Phabricator via llvm-commits]

aprantl accepted this revision.
aprantl added a comment.
This revision is now accepted and ready to land.

In https://reviews.llvm.org/D35994#854146, @NikolaPrica wrote:

> >> 
> >> 
> >>   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.


Cool. Thanks for checking!

> 
> 
>>>    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.

Oh, because it is a global variable! Makes sense.

> 
> 
>> 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?

That makes sense. I'm fine with not attempting to fix this.



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Comment at: test/Transforms/GlobalOpt/integer-bool-dwarf.ll:43
+
+attributes #0 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone speculatable }
----------------
please strip out all non-essential attributes (everything in quotes)


https://reviews.llvm.org/D35994