[libclc] Use __scoped_atomic_udec/uinc_wrap to implement _clc_atomic_dec/inc

[wenju-he]

No description provided.

[Copilot]

Pull Request Overview

This PR fixes a critical bug in the libclc atomic operation implementations where the increment and decrement functions were using the wrong underlying atomic operations. The __clc_atomic_inc function was incorrectly using __scoped_atomic_fetch_sub (subtraction) instead of __scoped_atomic_fetch_add (addition), and conversely, __clc_atomic_dec was using addition instead of subtraction.

• Corrected __clc_atomic_inc to use __scoped_atomic_fetch_add instead of __scoped_atomic_fetch_sub
• Corrected __clc_atomic_dec to use __scoped_atomic_fetch_sub instead of __scoped_atomic_fetch_add

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
libclc/clc/lib/generic/atomic/clc_atomic_inc.cl	Fixed atomic increment to use addition operation instead of subtraction
libclc/clc/lib/generic/atomic/clc_atomic_dec.cl	Fixed atomic decrement to use subtraction operation instead of addition

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[arsenm]

I think __clc_atomic_inc/dec should be deleted, or renamed. inc is a different op (i.e., atomicrmw uinc_wrap)

[wenju-he]

I think __clc_atomic_inc/dec should be deleted, or renamed. inc is a different op (i.e., atomicrmw uinc_wrap)

can we add new __scoped_atomic_uinc_wrap/udec_wrap clang builtin and use it for __clc_atomic_inc/dec implementation?
our downstream implementation of __clc_atomic_inc does use uinc_wrap in atomicrmw.

[arsenm]

I think __clc_atomic_inc/dec should be deleted, or renamed. inc is a different op (i.e., atomicrmw uinc_wrap)

can we add new __scoped_atomic_uinc_wrap/udec_wrap clang builtin and use it for __clc_atomic_inc/dec implementation? our downstream implementation of __clc_atomic_inc does use uinc_wrap in atomicrmw.

Yes, should do that

[wenju-he]

I think __clc_atomic_inc/dec should be deleted, or renamed. inc is a different op (i.e., atomicrmw uinc_wrap)

can we add new __scoped_atomic_uinc_wrap/udec_wrap clang builtin and use it for __clc_atomic_inc/dec implementation? our downstream implementation of __clc_atomic_inc does use uinc_wrap in atomicrmw.

Yes, should do that

changed to use __scoped_atomic_uinc_wrap for __clc_atomic_inc and __scoped_atomic_udec_wrap for __clc_atomic_dec

[arsenm]

I take it this function was just completely broken before? Is there no testing for it anywhere?

[wenju-he]

I take it this function was just completely broken before? Is there no testing for it anywhere?

Yes.
I'll use them for our downstream target, then it will be tested.