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decompress: refine data depdency

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The final ip advance value doesn't have to wait for
the result of offset to load *tag. It can be computed
along with the offset, so the codegen will use one
csinc in parallel with ldrb. This will improve the
throughput.
With this change it is observed ~4.2% uplift in UFlat/10
and ~3.7% in UFlatMedley

Signed-off-by: Jun He <jun.he@arm.com>
Change-Id: I20ab211235bbf578c6c978f2bbd9160a49e920da
This commit is contained in:
Jun He
2021-08-17 16:36:43 +08:00
parent 7062d7f1d8
commit aeb5de55a9
1 changed files with 8 additions and 4 deletions
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snappy.cc
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@@ -1015,12 +1015,16 @@ size_t AdvanceToNextTagARMOptimized(const uint8_t** ip_p, size_t* tag) {
// delta2 = ((c >> 2) + 1) ip++ // delta2 = ((c >> 2) + 1) ip++
// This is different from X86 optimizations because ARM has conditional add // This is different from X86 optimizations because ARM has conditional add
// instruction (csinc) and it removes several register moves. // instruction (csinc) and it removes several register moves.
const size_t literal_tag_offset = (*tag >> 2) + 1;
const size_t tag_type = *tag & 3; const size_t tag_type = *tag & 3;
const bool is_literal = (tag_type == 0); const bool is_literal = (tag_type == 0);
*tag = is_literal ? ip[literal_tag_offset] : ip[tag_type]; if (is_literal) {
ip += is_literal ? literal_tag_offset : tag_type; size_t next_literal_tag = (*tag >> 2) + 1;
ip++; *tag = ip[next_literal_tag];
ip += next_literal_tag + 1;
} else {
*tag = ip[tag_type];
ip += tag_type + 1;
}
return tag_type; return tag_type;
} }