[NVPTX] Incorrect alignment in call prototype for 'sprintf' function

[jhuber6]

The NVPTX backend currently emits the incorrect alignment when trying to compile the sprintf function with LTO. It will emit errors like the following:

ptxas a.s, line 1509; error   : Alignment of argument does not match formal parameter '_'

Looking at the IR in https://godbolt.org/z/n9nK6ddxb I noticed that many of these _ function calls come from the main implementation. If this function is internalized, then these calls get an incorrect alignment of 16 as in the following:

prototype_82 : .callprototype (.param .b32 _) _ (.param .align 16 .b8 _[16], .param .b64 _);

If I make the indirect call instead have an alignment of 8, then it works just fine, i.e. This also happens if I manually remove the internal keyword from the function and thus make it .visible.

prototype_82 : .callprototype (.param .b32 _) _ (.param .align 8 .b8 _[16], .param .b64 _);

Any clue why this would cause issues? Since this is an indirect call it's not like there's a set prototype we need to adhere to. And I don't see why making the function .visible or not makes the alignment correct.

[jhuber6]

@Artem-B Any ideas? I've disabled sprintf in the NVPTX tester for now.

[jhuber6]

I have made a smaller reproducer https://godbolt.org/z/G7da6s6Yz. This will give the same error,

ptxas /tmp/indirect-3cf878.s, line 89; error   : Alignment of argument does not match formal parameter '_'

If the alignment is modified to be 1 instead it will work.

[jhuber6]

/cherry-pick e0649a5

[llvmbot]

/pull-request #100174