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Remove some unnecessary initialization in seq operations (#22677)

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* `PrepareSeqAdd`
* `add`
* `setLen`
* `grow`

Merge after #21842.

---------

Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>
This commit is contained in:
Amjad Ben Hedhili
2023-09-10 16:36:49 +01:00
committed by GitHub
parent f8f6a3c926
commit fbb5ac512c
1 changed files with 35 additions and 7 deletions
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42
lib/system/seqs_v2.nim
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@@ -79,15 +79,42 @@ proc prepareSeqAdd(len: int; p: pointer; addlen, elemSize, elemAlign: int): poin
var p = cast[ptr NimSeqPayloadBase](p)
let oldCap = p.cap and not strlitFlag
let newCap = max(resize(oldCap), len+addlen)
var q: ptr NimSeqPayloadBase
if (p.cap and strlitFlag) == strlitFlag:
var q = cast[ptr NimSeqPayloadBase](alignedAlloc0(headerSize + elemSize * newCap, elemAlign))
q = cast[ptr NimSeqPayloadBase](alignedAlloc(headerSize + elemSize * newCap, elemAlign))
copyMem(q +! headerSize, p +! headerSize, len * elemSize)
else:
let oldSize = headerSize + elemSize * oldCap
let newSize = headerSize + elemSize * newCap
q = cast[ptr NimSeqPayloadBase](alignedRealloc(p, oldSize, newSize, elemAlign))
zeroMem(q +! headerSize +! len * elemSize, addlen * elemSize)
q.cap = newCap
result = q
proc prepareSeqAddUninit(len: int; p: pointer; addlen, elemSize, elemAlign: int): pointer {.
noSideEffect, tags: [], raises: [], compilerRtl.} =
{.noSideEffect.}:
let headerSize = align(sizeof(NimSeqPayloadBase), elemAlign)
if addlen <= 0:
result = p
elif p == nil:
result = newSeqPayloadUninit(len+addlen, elemSize, elemAlign)
else:
# Note: this means we cannot support things that have internal pointers as
# they get reallocated here. This needs to be documented clearly.
var p = cast[ptr NimSeqPayloadBase](p)
let oldCap = p.cap and not strlitFlag
let newCap = max(resize(oldCap), len+addlen)
if (p.cap and strlitFlag) == strlitFlag:
var q = cast[ptr NimSeqPayloadBase](alignedAlloc(headerSize + elemSize * newCap, elemAlign))
copyMem(q +! headerSize, p +! headerSize, len * elemSize)
q.cap = newCap
result = q
else:
let oldSize = headerSize + elemSize * oldCap
let newSize = headerSize + elemSize * newCap
var q = cast[ptr NimSeqPayloadBase](alignedRealloc0(p, oldSize, newSize, elemAlign))
var q = cast[ptr NimSeqPayloadBase](alignedRealloc(p, oldSize, newSize, elemAlign))
q.cap = newCap
result = q
@@ -104,16 +131,17 @@ proc shrink*[T](x: var seq[T]; newLen: Natural) {.tags: [], raises: [].} =
{.noSideEffect.}:
cast[ptr NimSeqV2[T]](addr x).len = newLen
proc grow*[T](x: var seq[T]; newLen: Natural; value: T) =
proc grow*[T](x: var seq[T]; newLen: Natural; value: T) {.nodestroy.} =
let oldLen = x.len
#sysAssert newLen >= x.len, "invalid newLen parameter for 'grow'"
if newLen <= oldLen: return
var xu = cast[ptr NimSeqV2[T]](addr x)
if xu.p == nil or (xu.p.cap and not strlitFlag) < newLen:
xu.p = cast[typeof(xu.p)](prepareSeqAdd(oldLen, xu.p, newLen - oldLen, sizeof(T), alignof(T)))
xu.p = cast[typeof(xu.p)](prepareSeqAddUninit(oldLen, xu.p, newLen - oldLen, sizeof(T), alignof(T)))
xu.len = newLen
for i in oldLen .. newLen-1:
xu.p.data[i] = value
wasMoved(xu.p.data[i])
`=copy`(xu.p.data[i], value)
proc add*[T](x: var seq[T]; y: sink T) {.magic: "AppendSeqElem", noSideEffect, nodestroy.} =
## Generic proc for adding a data item `y` to a container `x`.
@@ -126,7 +154,7 @@ proc add*[T](x: var seq[T]; y: sink T) {.magic: "AppendSeqElem", noSideEffect, n
let oldLen = x.len
var xu = cast[ptr NimSeqV2[T]](addr x)
if xu.p == nil or (xu.p.cap and not strlitFlag) < oldLen+1:
xu.p = cast[typeof(xu.p)](prepareSeqAdd(oldLen, xu.p, 1, sizeof(T), alignof(T)))
xu.p = cast[typeof(xu.p)](prepareSeqAddUninit(oldLen, xu.p, 1, sizeof(T), alignof(T)))
xu.len = oldLen+1
# .nodestroy means `xu.p.data[oldLen] = value` is compiled into a
# copyMem(). This is fine as know by construction that
@@ -143,7 +171,7 @@ proc setLen[T](s: var seq[T], newlen: Natural) {.nodestroy.} =
if newlen <= oldLen: return
var xu = cast[ptr NimSeqV2[T]](addr s)
if xu.p == nil or (xu.p.cap and not strlitFlag) < newlen:
xu.p = cast[typeof(xu.p)](prepareSeqAdd(oldLen, xu.p, newlen - oldLen, sizeof(T), alignof(T)))
xu.p = cast[typeof(xu.p)](prepareSeqAddUninit(oldLen, xu.p, newlen - oldLen, sizeof(T), alignof(T)))
xu.len = newlen
for i in oldLen..<newlen:
xu.p.data[i] = default(T)