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gallium/indices: Use "__restrict" to help the compiler

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In a perf trace translate_quads_uint2uint_last2last_prdisable() was
showing up as a huge hot spot. Digging through the assembly on arm64
found that the compiler wasn't doing any read caching. Specifically,
the generated code looked roughly like this:

  out[j+0] = in[i+0];
  out[j+1] = in[i+1];
  out[j+2] = in[i+3];
  out[j+3] = in[i+1];
  out[j+4] = in[i+2];
  out[j+5] = in[i+3];

...and the compiler was loading "i+1" and "i+3" from memory twice for
no reason (instead of caching it).

If we sprinkle generous amounts of the `__restrict` keyword then the
compiler is able to be much smarter. Not only does it avoid
double-loading but it also generates better instructions. It uses two
LDRD instructions instead of 6 LDR instructions and uses some STRD
too.

In one example test this increased FPS from ~25.7 to ~34.5.

Change-Id: I88bf8bd9ac421fe48a7d6961e224425c3ae7beee
Reported-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9485>
This commit is contained in:
Douglas Anderson
2021-03-09 11:10:43 -08:00
committed by Marge Bot
parent e7e297732e
commit 217d6594de
1 changed files with 4 additions and 4 deletions
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src/gallium/auxiliary/indices/u_indices_gen.py
+4 -4
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@@ -190,18 +190,18 @@ def name(intype, outtype, inpv, outpv, pr, prim):
def preamble(intype, outtype, inpv, outpv, pr, prim):
print('static void ' + name( intype, outtype, inpv, outpv, pr, prim ) + '(')
if intype != GENERATE:
print(' const void * _in,')
print(' const void * restrict _in,')
print(' unsigned start,')
if intype != GENERATE:
print(' unsigned in_nr,')
print(' unsigned out_nr,')
if intype != GENERATE:
print(' unsigned restart_index,')
print(' void *_out )')
print(' void * restrict _out )')
print('{')
if intype != GENERATE:
print(' const ' + intype + '*in = (const ' + intype + '*)_in;')
print(' ' + outtype + ' *out = (' + outtype + '*)_out;')
print(' const ' + intype + '* restrict in = (const ' + intype + '* restrict)_in;')
print(' ' + outtype + ' * restrict out = (' + outtype + '* restrict)_out;')
print(' unsigned i, j;')
print(' (void)j;')