[PATCH] D20262: [DSE]Split memset when the memset is small enough to be lowered to stores

[Mehdi Amini via llvm-commits]

> On Jun 1, 2016, at 8:47 AM, Jun Bum Lim <junbuml at codeaurora.org> wrote:
> 
> junbuml added a comment.
> 
>> http://llvm.org/docs/doxygen/html/Module_8cpp_source.html#l00375
> 
>> "const DataLayout &Module::getDataLayout() const { return DL; }"
> 
>> It returns a reference, so it is guaranteed to not be null.
> 
>> "No data layout in the Textual IR means "use the default data layout" for the triple."
> 
> 
> Thanks for clarifying this. So, we are guaranteed to DL even without datalayout in the textual IR. However, this doesn't mean that we can always get the non-zero from DL.getLargestLegalIntTypeSizeInBits().  As I test, we can use an empty datalayout in IR like : target datalayout="".

I feel you are speculating, and haven't really tried the effects of what your describing, neither look at the code that constructs a DataLayout.
Writing this in textual IR is identical to not write anything.


> 
>> Wouldn't DL.getLargestLegalIntTypeSizeInBits() == 0 imply that you can have icmp or select? Hence almost nothing in llvm would work?
> 
> 
> Although we can make DL.getLargestLegalIntTypeSizeInBits() return  0,

Please write a test case.


> I also doubt when this is meaningful. If this doesn't make sense,
> I will add  assert in getLargestLegalIntTypeSizeInBits().

I don't think such an assert makes sense here, on a function that is frequently called.
If you insist on verifying properties on the DataLayout, do it in reset().

>  Can anyone give us any feedback if there is any situation where we need to consider getLargestLegalIntTypeSizeInBits() == 0 ?  As far as I test, I didn't see any unit test failure with the assert in getLargestLegalIntTypeSizeInBits() == 0.

Not surprising...


-- 
Mehdi