fixes#25007
```nim
proc setLengthSeqUninit(s: PGenericSeq, typ: PNimType, newLen: int, isTrivial: bool): PGenericSeq {.
compilerRtl.} =
```
In this added function, only the line `zeroMem(dataPointer(result,
elemAlign, elemSize, newLen), (result.len-%newLen) *% elemSize)` is
removed from `proc setLengthSeqV2` when enlarging a sequence.
JS and VM versions simply use `setLen`.
(cherry picked from commit 611b8bbf67)
Raising exceptions halfway through a memory allocation is undefined
behavior since exceptions themselves require multiple allocations and
the allocator functions are not reentrant.
It is of course also expensive performance-wise to introduce lots of
exception-raising code everywhere since it breaks many optimisations and
bloats the code.
Finally, performing pointer arithmetic with signed integers is incorrect
for example on on a 32-bit systems that allows up to 3gb of address
space for applications (large address extensions) and unnecessary
elsewhere - broadly, stuff inside the memory allocator is generated by
the compiler or controlled by the standard library meaning that
applications should not be forced to pay this price.
If we wanted to check for overflow, the right way would be in the
initial allocation location where both the size and count of objects is
known.
The code is updated to use the same arithmetic operator style as for
refc with unchecked operations rather than disabling overflow checking
wholesale in the allocator module - there are reasons for both, but
going with the existing flow seems like an easier place to start.
(cherry picked from commit 8b9972c8b6)
* fix/workaround for nimrtl and nimhcr on arc/orc
fixes#21803
* try fix clang, debug linux failure
* just make duplicated procs not rtl
* actual fix for duplicated procs
* alternative, much simpler algorithm for strict func checking
* forgot to git add new compiler module
* new spec is incredibly simple to describe
* fixes bigints regression
* typos
* closes#16305; closes#17387; closes#20863
* Cleanup, remove lib/system/allocators.nim. seqs_v2 and strs_v2 now use
allocShared0 by default.
* Fixed -d:useMalloc allocShared / reallocShared / deallocShared. These now use the alloc/dealloc/realloc implementation that also takes care of zeroing memory at realloc.
* Removed debug printfs
* Removed unpairedEnvAllocs() from tests/destructor/tnewruntime_misc
* More mmdisp cleanups. The shared allocators do not need to zero memory or throw since the regular ones already do that
* Introduced realloc0 and reallocShared0, these procs are now used by
strs_v2 and seqs_v2. This also allowed the -d:useMalloc allocator to
drop the extra header with allocation length.
* Moved strs_v2/seqs_v2 'allocated' flag into 'cap' field
* Added 'getAllocStats()' to get low level alloc/dealloc counters. Enable with -d:allocStats
* *allocShared implementations for boehm and go allocators now depend on the proper *allocImpl procs
* fixes#13102
* closes#13149
* ARC: fixes a move optimizer bug (there are more left regarding array and tuple indexing)
* proper fix; fixes#12957
* fixes yet another case object '=' code generation problem
* first implementation of the =trace and =dispose hooks for the cycle collector
* a cycle collector for ARC: progress
* manual: the .acyclic pragma is a thing once again
* gcbench: adaptations for --gc:arc
* enable valgrind tests for the strutils tests
* testament: better valgrind support
* ARC refactoring: growable jumpstacks
* ARC cycle detector: non-recursive algorithm
* moved and renamed core/ files back to system/
* refactoring: --gc:arc vs --gc:orc since 'orc' is even more experimental and we want to ship --gc:arc soonish
