[llvm-branch-commits] [clang] [llvm] [SPARC] Prefer RDPC over CALL to implement GETPCX for 64-bit target (PR #77196)

[via llvm-branch-commits]

https://github.com/koachan created https://github.com/llvm/llvm-project/pull/77196

On 64-bit target, prefer usng RDPC over CALL to get the value of %pc.
This is faster on modern processors (Niagara T1 and newer) and avoids polluting
the processor's predictor state.

The old behavior of using a fake CALL is still done when tuning for classic
UltraSPARC processors, since RDPC is much slower there.

A quick pgbench test on a SPARC T4 shows about 2% speedup on SELECT loads,
and about 7% speedup on INSERT/UPDATE loads.