tree d939e26a07156428a9ed24c6d08c7a3451ecc31d
parent 04fecd2a331388286f2aaf05450f37bc288e0476
author Andre Przywara <andre.przywara@arm.com> 1668422388 +0000
committer Andre Przywara <andre.przywara@arm.com> 1673452977 +0000

feat(aarch64): make ID system register reads non-volatile

Our system register access function wrappers are using "volatile"
inline assembly instructions. On the first glance this is a good idea,
since many system registers have side effects, and we don't want the
compiler to optimise or reorder them (what "volatile" prevents).

However this also naturally limits the compiler's freedom to optimise
code better, and those volatile properties don't apply to every type of
system register. One example are the CPU ID registers, which have
constant values, are side-effect free and read-only.

Introduce a new wrapper type that drops the volatile keyword, and use
that for the wrappers instantiating ID register accessors.

This allows the compiler to freely optimise those instructions away, if
their result isn't actually used, which can trigger further
optimisations.

Change-Id: I3c64716ae4f4bf603f0ea57b652bd50bcc67bb0e
Signed-off-by: Andre Przywara <andre.przywara@arm.com>