On Sat, 22 Oct 2022, Martin Sebor wrote: > On 10/21/22 09:29, Qing Zhao wrote: > > Hi, > > > > (FAM below refers to Flexible Array Members): > > > > I need inputs on how to handle the combination of -fstrict-flex-arrays + > > -Warray-bounds. > > > > Our initial goal is to update -Warray-bounds with multiple levels of > > -fstrict-flex-arrays=N > > to issue warnings according to the different levels of ?N?. > > However, after detailed study, I found that this goal was very hard to be > > achieved. > > > > 1. -fstrict-flex-arrays and its levels > > > > The new option -fstrict-flex-arrays has 4 levels: > > > > level trailing arrays > > treated as FAM > > > > 0 [],[0],[1],[n] the default without option > > 1 [],[0],[1] > > 2 [],[0] > > 3 [] the default when option specified > > without value > > > > 2. -Warray-bounds and its levels > > > > The option -Warray-bounds currently has 2 levels: > > > > level trailing arrays > > treated as FAM > > > > 1 [],[0],[1] the default when option specified > > without value > > 2 [] > > > > i.e, > > When -Warray-bounds=1, it treats [],[0],[1] as FAM, the same level as > > -fstrict-flex-arrays=1; > > When -Warray-bounds=2, it only treat [] as FAM, the same level as > > -fstrict-flex-arrays=3; > > > > 3. How to handle the combination of -fstrict-flex-arrays and > > -Warray-bounds? > > > > Question 1: when -fstrict-flex-arrays does not present, the default is > > -strict-flex-arrays=0, > > which treats [],[0],[1],[n] as FAM, so should we update > > the default behavior > > of -Warray-bounds to treat any trailing array [n] as > > FAMs? > > > > My immediate answer to Q1 is NO, we shouldn?t, that will be a big regression > > on -Warray-bounds, right? > > Yes, it would disable -Warray-bounds in the cases where it warns > for past-the-end accesses to trailing arrays with two or more > elements. Diagnosing those has historically (i.e., before recent > changes) been a design goal. > > > > > Question 2: when -fstrict-flex-arrays=N1 and -Warray-bounds=N2 present at > > the same time, > > Which one has higher priority? N1 or N2? > > > > -fstrict-flex-arrays=N1 controls how the compiler code generation treats the > > trailing arrays as FAMs, it seems > > reasonable to give higher priority to N1, > > I tend to agree. In other words, set N2' = min(N1, N2).
Yes. Or do nothing and treat them independently. Can you check whether it's possible to distinguish -Warray-bounds from -Warray-bounds=N? I'd say that explicit -Warray-bounds=N should exactly get the documented set of diagnostis, independent of -fstrict-flex-arrays=N. > > However, then should we completely disable the level of -Warray-bounds > > N2 under such situation? > > > > I really don?t know what?s the best way to handle the conflict between N1 > > and N2. > > > > Can we completely cancel the 2 levels of -Warray-bounds, and always honor > > the level of -fstrict-flex-arrays? > > > > Any comments or suggestion will be helpful. > > The recent -fstrict-flex-array changes aside, IIRC, there's only > a subtle distinction between the two -Warray-bounds levels (since > level 1 started warning on a number of instances that only level > 2 used to diagnose a few releases ago). I think that subset of > level 2 could be merged into level 1 without increasing the rate > of false positives. Then level 2 could be assigned a new set of > potential problems to detect (such as past-the-end accesses to > trailing one-element arrays). > > Martin > > -- Richard Biener <rguent...@suse.de> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman; HRB 36809 (AG Nuernberg)
