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fixes #19728; setLen slow when shrinking seq due to zero-filling of released area (#24683)

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fixes #19728

don't zero-filling memory for "trivial types" without destructor in
refc. I tested locally with internal apis.

(cherry picked from commit b421d0f8ee)
This commit is contained in:
ringabout
2025-02-27 23:45:58 +08:00
committed by narimiran
parent 5394c6814b
commit fcf4f10c70
3 changed files with 40 additions and 4 deletions
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5
lib/system/sysstr.nim
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@@ -300,7 +300,7 @@ proc setLengthSeq(seq: PGenericSeq, elemSize, elemAlign, newLen: int): PGenericS
zeroMem(dataPointer(result, elemAlign, elemSize, newLen), (result.len-%newLen) *% elemSize)
result.len = newLen
proc setLengthSeqV2(s: PGenericSeq, typ: PNimType, newLen: int): PGenericSeq {.
proc setLengthSeqV2(s: PGenericSeq, typ: PNimType, newLen: int, isTrivial: bool): PGenericSeq {.
compilerRtl.} =
sysAssert typ.kind == tySequence, "setLengthSeqV2: type is not a seq"
if s == nil:
@@ -334,7 +334,8 @@ proc setLengthSeqV2(s: PGenericSeq, typ: PNimType, newLen: int): PGenericSeq {.
# presence of user defined destructors, the user will expect the cell to be
# "destroyed" thus creating the same problem. We can destroy the cell in the
# finalizer of the sequence, but this makes destruction non-deterministic.
zeroMem(dataPointer(result, elemAlign, elemSize, newLen), (result.len-%newLen) *% elemSize)
if not isTrivial: # optimization for trivial types
zeroMem(dataPointer(result, elemAlign, elemSize, newLen), (result.len-%newLen) *% elemSize)
else:
result = s
zeroMem(dataPointer(result, elemAlign, elemSize, result.len), (newLen-%result.len) *% elemSize)