[-Wunsafe-buffer-usage] Ignore constant safe indices in array subscri… #8196
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…pts (llvm#80504) [-Wunsafe-buffer-usage] Ignore safe array subscripts Don't emit warnings for array subscripts on constant size arrays where the index is constant and within bounds. Example: int arr[10]; arr[5] = 0; //safe, no warning This patch recognizes only array indices that are integer literals - it doesn't understand more complex expressions (arithmetic on constants, etc.). -Warray-bounds implemented in Sema::CheckArrayAccess() already solves a similar (opposite) problem, handles complex expressions and is battle-tested. Adding -Wunsafe-buffer-usage diagnostics to Sema is a non-starter as we need to emit both the warnings and fixits and the performance impact of the fixit machine is unacceptable for Sema. CheckArrayAccess() as is doesn't distinguish between "safe" and "unknown" array accesses. It also mixes the analysis that decides if an index is out of bounds with crafting the diagnostics. A refactor of CheckArrayAccess() might serve both the original purpose and help us avoid false-positive with -Wunsafe-buffer-usage on constant size arrrays. (cherry picked from commit 9a1e637)
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…pts (llvm#80504)
[-Wunsafe-buffer-usage] Ignore safe array subscripts Don't emit warnings for array subscripts on constant size arrays where the index is constant and within bounds.
Example:
int arr[10];
arr[5] = 0; //safe, no warning
This patch recognizes only array indices that are integer literals - it doesn't understand more complex expressions (arithmetic on constants, etc.).
-Warray-bounds implemented in Sema::CheckArrayAccess() already solves a similar (opposite) problem, handles complex expressions and is battle-tested.
Adding -Wunsafe-buffer-usage diagnostics to Sema is a non-starter as we need to emit both the warnings and fixits and the performance impact of the fixit machine is unacceptable for Sema.
CheckArrayAccess() as is doesn't distinguish between "safe" and "unknown" array accesses. It also mixes the analysis that decides if an index is out of bounds with crafting the diagnostics.
A refactor of CheckArrayAccess() might serve both the original purpose and help us avoid false-positive with -Wunsafe-buffer-usage on constant size arrrays.
(cherry picked from commit 9a1e637)