alt-ergo goals generated directly / via why3 differ in provability
ID0002353: This issue was created automatically from Mantis Issue 2353. Further discussion may take place here.
| Id | Project | Category | View | Due Date | Updated |
|---|---|---|---|---|---|
| ID0002353 | Frama-C | Plug-in > wp | public | 2018-02-01 | 2019-10-17 |
| Reporter | Jochen | Assigned To | correnson | Resolution | no change required |
| Priority | normal | Severity | minor | Reproducibility | always |
| Platform | Sulfur-20171101 | OS | - | OS Version | Ubuntu 17.04 |
| Product Version | Frama-C 16-Sulfur | Target Version | - | Fixed in Version | - |
Description :
I generated an Alt-Ergo proof obligation for the ensures clause "xxx" (line 1140) of the attached program "search_n_standalone.c" (which was obtained from "search_n" in "Acsl by example" by "gcc -E -C"). When I did this directly (see attached script "fd"), it was proven without problems. However, when I did this via Why3 (see script "fw"), Alt-Ergo responded "Don't know" after 0.1 seconds.
In order to compare both mlw files given to Alt-Ergo, I moved the goal of the via-Why3 file into the direct file; it became provable there. Removing as many axioms and definitions as possible while keeping the (non-)provability, I obtained the files "xxx_direct.mlw" and "xxx_via_why3.mlw". It seems that the former defines and uses "shift_sint32", while the latter does not (it uses "shift" instead). Probably, this is the reason for the different outcomes of Alt-Ergo.
Although the observed issue may not be bug (both mlw files may be semanically equivalent), it might be desirable to unify the proof obligations given to Alt-Ergo on different pathways.