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drm/i915: Make ptr_unpack_bits() more function-like 

ptr_unpack_bits() is a function-like macro, as such it is meant to be
replaceable by a function. In this case, we should be passing in the
out-param as a pointer.

Bizarrely this does affect code generation:

function                                     old     new   delta
i915_gem_object_pin_map                      409     389     -20

An improvement(?) in this case, but one can't help wonder what
strict-aliasing optimisations we are preventing.

The generated code looks identical in using ptr_unpack_bits (no extra
motions to stack, the pointer and bits appear to be kept in registers),
the difference appears to be code ordering and with a reorder it is able
to use smaller forward jumps.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170517121007.27224-3-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2017-05-17 13:09:58 +01:00
parent 47624cc330
commit 991bfc64db
2 changed files with 2 additions and 2 deletions
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2
drivers/gpu/drm/i915/i915_gem.c
View File

@ -2612,7 +2612,7 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
}
GEM_BUG_ON(!obj->mm.pages);
ptr = ptr_unpack_bits(obj->mm.mapping, has_type);
ptr = ptr_unpack_bits(obj->mm.mapping, &has_type);
if (ptr && has_type != type) {
if (pinned) {
ret = -EBUSY;

2
drivers/gpu/drm/i915/i915_utils.h
View File

@ -77,7 +77,7 @@
#define ptr_unpack_bits(ptr, bits) ({ \
unsigned long __v = (unsigned long)(ptr); \
(bits) = __v & ~PAGE_MASK; \
*(bits) = __v & ~PAGE_MASK; \
(typeof(ptr))(__v & PAGE_MASK); \
})