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Bug 24226 – operator `~=` appears to lead to useless bound checks

Status: RESOLVED
Resolution: INVALID
Severity: normal
Priority: P1
Component: dmd
Product: D
Version: D2
Platform: All
OS: All
Creation time: 2023-11-04T12:59:29Z
Last change time: 2023-11-09T09:51:19Z
Assigned to: No Owner
Creator: Basile-z

Comments

Comment #0 by b2.temp — 2023-11-04T12:59:29Z

For the following code: ``` extern(C) int printf(const char* f, ...); int main() { const(char)[] fmt; fmt ~= "\n\0"; return 0; } ``` The output assembly show calls related to bound checks https://godbolt.org/z/nKhsEWvoT, apparently in the runtime functions. But can bounds be violated here ?

Comment #1 by b2.temp — 2023-11-04T13:35:05Z

oh, that's for size_t overflow I guess.

Comment #2 by razvan.nitu1305 — 2023-11-09T09:51:19Z

The hook itself uses some arrays internally to access the data, as can be seen from the source code: https://github.com/dlang/dmd/blob/master/druntime/src/core/internal/array/appending.d#L89 . Those accesses are protected by array bounds check. No bug here.