[FFmpeg-devel] [PATCH 1/5] lavu/common.h: Fix UB in av_clipl_int32_c()

[Rémi Denis-Courmont]

Le torstaina 30. toukokuuta 2024, 22.07.13 EEST Michael Niedermayer a écrit :
> If the function doesnt get called with values triggering UB then its not UB.

As Tomas pointed out, that statement is actually false. Specifically, if the 
compiler can prove that the function can be called with values triggering UB, 
then the code is UB, even if those offending values do not actually occur in a 
given instance of the program.

The C specification is known to contradict causality.

For instance, if you have pass an uninitialised value to av_clipl_int32_c(), 
then the code is UB, even if the actual value in the register or stack slot is 
never one that could trigger UB. Of course, usage of uninitialised values is a 
bad practice, but it is not, per se, UB.

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