orc: fix overflow checking regression #25089
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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.
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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.