Frama-C Bug Tracking System - Frama-C | ||||||||||
| View Issue Details | ||||||||||
| ID | Project | Category | View Status | Date Submitted | Last Update | |||||
| 0000325 | Frama-C | Plug-in > Eva | public | 2009-11-07 12:05 | 2014-02-12 16:55 | |||||
| Reporter | pascal | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Assigned To | pascal | |||||||||
| Priority | normal | Severity | feature | Reproducibility | always | |||||
| Status | closed | Resolution | fixed | |||||||
| Platform | OS | OS Version | ||||||||
| Product Version | Frama-C Beryllium-20090902 | |||||||||
| Target Version | Fixed in Version | Frama-C Boron-20100401 | ||||||||
| Summary | 0000325: Precise widening when a loop condition involves a char or short | |||||||||
| Description | > Depending the type of i, the range is not the same. > The range of i in the loop is [0..10] (for int) or [0..15] for char or > short. _____ void main(void) { char i=0; int j=0; while (i<10) i++; while (j<10) j++; } [value] ====== VALUES COMPUTED ====== [value] Values for function main: i IN {10; 11; 12; 13; 14; 15; } j IN {10; } _____ Note that the AST for the two loops is different: i = (char)0; j = 0; while ((int )i < 10) {i = (char )((int )i + 1);} while (j < 10) {j ++;} CIL transforms the code thus because the standard specifies that operators such as ++ do not operate on types smaller than int, and that values of these types are implicitly promoted to int in these conditions. Meanwhile, in the absence of any loop-related option, the value analysis tries to keep computations short at the price of precision by using a technique called "widening". In order to limit the loss of precision, however, various heuristics are used, including a syntactic one for the j loop that recognizes that j IN [0..10] is a good candidate for the loop invariant. These heuristic does not currently recognize the condition ((int )i < 10) as one where it would be valuable to try the same kind of invariant. | |||||||||
| Tags | No tags attached. | |||||||||
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| Issue History | |||||
| Date Modified | Username | Field | Change | ||
|---|---|---|---|---|---|
| 2009-11-07 12:05 | pascal | New Issue | |||
| 2009-11-07 12:05 | pascal | Status | new => assigned | ||
| 2009-11-07 12:05 | pascal | Assigned To | => pascal | ||
| 2010-02-19 14:46 | pascal | Relationship added | has duplicate 0000414 | ||
| 2010-02-19 16:09 | svn | ||||
| 2010-02-19 16:09 | svn | Status | assigned => resolved | ||
| 2010-02-19 16:09 | svn | Resolution | open => fixed | ||
| 2010-04-13 15:30 | signoles | Status | resolved => new | ||
| 2010-04-13 15:31 | signoles | Status | new => closed | ||
| 2010-04-13 15:33 | signoles | Fixed in Version | => Frama-C Boron | ||
| 2013-12-19 01:13 | pascal | Source_changeset_attached | => framac master 32fe36a6 | ||
| 2014-02-12 16:55 | pascal | Source_changeset_attached | => framac stable/neon 32fe36a6 | ||
| 2018-01-12 14:26 | signoles | Category | Plug-in > value analysis => Plug-in > Eva | ||