Aaditya 11b0401926 [AMDGPU] Restore SP from saved-FP or saved-BP (#124007) ...

Currently, the AMDGPU backend bumps the Stack Pointer 
by fixed size offsets in the prolog of device functions, and 
restores it by the same amount in the epilog.
Prolog:
sp += frameSize

Epilog:
sp -= frameSize

If a function has dynamic stack realignment,
Prolog:
sp += frameSize + max_alignment

Epilog:
sp -= frameSize + max_alignment

These calculations are not optimal in case of dynamic 
stack realignment, and completely fail in case of 
dynamic stack readjustment.
This patch uses the saved Frame Pointer to restore SP. 
Prolog:
fp = sp
sp += frameSize

Epilog:
sp = fp

In case of dynamic stack realignment, SP is restored from 
the saved Base Pointer. 
Prolog:
fp = sp + (max_alignment - 1)
fp = fp & (-max_alignment)
bp = sp
sp += frameSize + max_alignment

Epilog:
sp = bp

(Note: The presence of BP has been enforced in case of any 
dynamic stack realignment.)

---------

Co-authored-by: Pravin Jagtap <Pravin.Jagtap@amd.com>
Co-authored-by: Matt Arsenault <arsenm2@gmail.com>

2025-01-24 19:13:40 +05:30

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