[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

[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>

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AMDGPU: Do not tail call if an inreg argument requires waterfalling (#111002)

If we have a divergent value passed to an outgoing inreg argument,
the call needs to be executed in a waterfall loop and

AMDGPU: Do not tail call if an inreg argument requires waterfalling (#111002)

If we have a divergent value passed to an outgoing inreg argument,
the call needs to be executed in a waterfall loop and thus cannot
be tail called.

The waterfall handling of arbitrary calls is broken on the selectiondag
path, so some of these cases still hit an error later.

I also noticed the argument evaluation code in isEligibleForTailCallOptimization
is not correctly accounting for implicit argument assignments. It also seems
inreg codegen is generally broken; we are assigning arguments to the reserved
private resource descriptor.

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