arm64: pgtable: convert pte_present() from macro to static inline

pte_present() is used as the basis for both pmd_present() and pud_present().
It is currently implemented as a macro composed of pte_val() and
pte_present_invalid().

When pte_present() or its higher-level variants are used directly with
ptep_get() or pXdp_get(), for example:

  pte_present(ptep_get(pte));
  pmd_present(pmdp_get(pmd));
  pud_present(pudp_get(pud));

the macro expansion causes the compiler to evaluate the argument twice,
resulting in redundant loads. For example, pte_present() expands to:

  !pte_val(READ_ONCE(*pte) || pte_present_invalid(READ_ONCE(*pte))

A typical example is pud_free_pmd_page(), where the expansion of
pmd_present() generates:
    ...
    /* pmd_present() (x20 = pmdp) */
    1b88: f9400288     ldr	x8, [x20]        // read pmdp.
    1b8c: f9000fa8     str	x8, [x29, #0x18]
    1b90: 3707fec8     tbnz	w8, #0x0, 0x1b68 <pud_free_pmd_page+0xd0>
    1b94: f9400288     ldr	x8, [x20]        // redundant read of pmdp.
    1b98: 8a170109     and	x9, x8, x23
    1b9c: f9000fa8     str	x8, [x29, #0x18]
    1ba0: f120013f     cmp	x9, #0x800
    1ba4: 54fffe20     b.eq	0x1b68 <pud_free_pmd_page+0xd0>
    1ba8: 17fffff4     b	0x1b78 <pud_free_pmd_page+0xe0>
    ...

Convert pte_present() to static inline function so that prevent the
generation of redundant code and move pte_valid() and
pte_present_invalid() further up so the inline function can use them.

After this change, the generated code becomes:
    ...
    /* pmd_present() (x20 = pmdp) */
    1a30: f9400288     ldr	x8, [x20]
    1a34: 8a170109     and	x9, x8, x23
    1a38: f9000fa8     str	x8, [x29, #0x18]
    1a3c: f120013f     cmp	x9, #0x800
    1a40: 54fffe80     b.eq	0x1a10 <pud_free_pmd_page+0xd0>
    1a44: 3607fee8     tbz	w8, #0x0, 0x1a20 <pud_free_pmd_page+0xe0>
    1a48: 17fffff2     b	0x1a10 <pud_free_pmd_page+0xd0>
    ...

This eliminates the redundant load and also reduces code size at
call sites using this pattern. For example, pud_free_pmd_page() shrinks
from 7,500 bytes to 7,148 bytes, a reduction of approximately 4.7%.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

0 files changed, 0 insertions, 0 deletions