[llvm-dev] i32 vs i32 signext for C int parameters to library functions

[Friedman, Eli via llvm-dev]

On 9/6/2016 4:10 AM, Marcin Kościelnicki via llvm-dev wrote:
> To fix this bug, I need some way to tell whether to use i32 or i32 
> signext in target-independent LLVM passes - but none seems to exist at 
> this moment.  I wrote a patch that adds this information to TTI ( 
> https://reviews.llvm.org/D21739 ), but it doesn't fit with the current 
> semantics of TTI - if the information about *ext is missing, we're 
> going to have correctness problems instead of merely lowered performance. 

The right answer here might be to put the information into 
TargetLibraryInfo.  Fundamentally, you're trying to answer something 
along the lines of "What's the correct signature for a call to 
memchr?".  This is the sort of question which TargetLibraryInfo already 
answers in other situations (for example, some standard libc functions 
have unusual names on some platforms).  If TargetLibraryInfo can't come 
up with the correct calling convention for a given function for whatever 
reason, it can just claim the function is unavailable, which preserves 
correctness.

-Eli

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