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ID0000325: This issue was created automatically from Mantis Issue 325. Further discussion may take place here.

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Id	Project	Category	View	Due Date	Updated
ID0000325	Frama-C	Plug-in > Eva	public	2009-11-07	2014-02-12

Reporter	pascal	Assigned To	pascal	Resolution	fixed
Priority	normal	Severity	feature	Reproducibility	always
Platform	-	OS	-	OS Version	-
Product Version	Frama-C Beryllium-20090902	Target Version	-	Fixed in Version	Frama-C Boron-20100401

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.

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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; }

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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.