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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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| .. | ||
| apicalls.lua | ||
| assert.lua | ||
| attrib.lua | ||
| basic.lua | ||
| bitwise.lua | ||
| buffers.lua | ||
| calls.lua | ||
| clear.lua | ||
| closure.lua | ||
| constructs.lua | ||
| coroutine.lua | ||
| coverage.lua | ||
| datetime.lua | ||
| debug.lua | ||
| debugger.lua | ||
| errors.lua | ||
| events.lua | ||
| exceptions.lua | ||
| gc.lua | ||
| ifelseexpr.lua | ||
| interrupt.lua | ||
| iter.lua | ||
| literals.lua | ||
| locals.lua | ||
| math.lua | ||
| move.lua | ||
| native.lua | ||
| native_types.lua | ||
| ndebug_upvalues.lua | ||
| pcall.lua | ||
| pm.lua | ||
| safeenv.lua | ||
| sort.lua | ||
| strconv.lua | ||
| stringinterp.lua | ||
| strings.lua | ||
| tables.lua | ||
| tmerror.lua | ||
| tpack.lua | ||
| types.lua | ||
| userdata.lua | ||
| utf8.lua | ||
| vararg.lua | ||
| vector.lua | ||