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f5303b3dd7
table.concat is idiomatic and should be the fastest way to concatenate
all table array elements together, but apparently you can beat it by
using `string.format`, `string.rep` and `table.unpack`:
```lua
string.format(string.rep("%*", #t), table.unpack(t))
```
... this just won't do, so we should fix table.concat performance.
The deficit comes from two places:
- rawgeti overhead followed by other stack accesses, all to extract a
string from what is almost always an in-bounds array lookup
- addlstring overhead in case separator is empty (extra function calls)
This change fixes this by using a fast path for in-bounds array lookup
for a string. Note that `table.concat` also supports numbers (these need
to be converted to strings which is a little cumbersome and has innate
overhead), and out-of-bounds accesses*. In these cases we fall back to
the old implementation.
To trigger out-of-bounds accesses, you need to skip the past-array-end
element (which is nil per array invariant), but this is achievable
because table.concat supports offset+length arguments. This should
almost never come up in practice but the per-element branches et al are
fairly cheap compared to the eventual string copy/alloc anyway.
This change makes table.concat ~2x faster when the separator is empty;
the table.concat benchmark shows +40% gains but it uses a variety of
string separators of different lengths so it doesn't get the full
benefit from this change.
---------
Co-authored-by: vegorov-rbx <75688451+vegorov-rbx@users.noreply.github.com>
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| .. | ||
| lapi.cpp | ||
| lapi.h | ||
| laux.cpp | ||
| lbaselib.cpp | ||
| lbitlib.cpp | ||
| lbuffer.cpp | ||
| lbuffer.h | ||
| lbuflib.cpp | ||
| lbuiltins.cpp | ||
| lbuiltins.h | ||
| lbytecode.h | ||
| lcommon.h | ||
| lcorolib.cpp | ||
| ldblib.cpp | ||
| ldebug.cpp | ||
| ldebug.h | ||
| ldo.cpp | ||
| ldo.h | ||
| lfunc.cpp | ||
| lfunc.h | ||
| lgc.cpp | ||
| lgc.h | ||
| lgcdebug.cpp | ||
| linit.cpp | ||
| lmathlib.cpp | ||
| lmem.cpp | ||
| lmem.h | ||
| lnumprint.cpp | ||
| lnumutils.h | ||
| lobject.cpp | ||
| lobject.h | ||
| loslib.cpp | ||
| lperf.cpp | ||
| lstate.cpp | ||
| lstate.h | ||
| lstring.cpp | ||
| lstring.h | ||
| lstrlib.cpp | ||
| ltable.cpp | ||
| ltable.h | ||
| ltablib.cpp | ||
| ltm.cpp | ||
| ltm.h | ||
| ludata.cpp | ||
| ludata.h | ||
| lutf8lib.cpp | ||
| lvm.h | ||
| lvmexecute.cpp | ||
| lvmload.cpp | ||
| lvmutils.cpp | ||