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Congruences: Make % sound by restricting cases where we return a constant #1161

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Sep 13, 2023
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Congruences: Make % sound by restricting cases where we return a constant #1161

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4 changes: 2 additions & 2 deletions src/cdomains/intDomain.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -3199,8 +3199,8 @@ struct
| None, _ | _, None -> raise (ArithmeticOnIntegerBot (Printf.sprintf "%s op %s" (show x) (show y)))
| Some (c1, m1), Some(c2, m2) ->
if m2 =: Ints_t.zero then
if (c2 |: m1) then
Some(c1 %: c2,Ints_t.zero)
if (c2 |: m1) && (c1 %: c2 =: Ints_t.zero || m1 =: Ints_t.zero || not (Cil.isSigned ik)) then
Some(c1 %: c2, Ints_t.zero)
else
normalize ik (Some(c1, (Ints_t.gcd m1 c2)))
else
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5 changes: 3 additions & 2 deletions tests/regression/37-congruence/06-refinements.c
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Expand Up @@ -5,14 +5,15 @@ int main() {
int top;
int i = 0;
if(top % 17 == 3) {
__goblint_check(top%17 ==3);
__goblint_check(top%17 ==3); //TODO (Refine top to be positive above, and reuse information in %)
if(top %17 != 3) {
i = 12;
} else {

}
}
__goblint_check(i ==0);
__goblint_check(i ==0); // TODO
i = 0;

if(top % 17 == 0) {
__goblint_check(top%17 == 0);
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5 changes: 3 additions & 2 deletions tests/regression/37-congruence/07-refinements-o.c
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Expand Up @@ -32,15 +32,16 @@ int main() {
int top;
int i = 0;
if(top % 17 == 3) {
__goblint_check(top%17 ==3);
__goblint_check(top%17 ==3); //TODO (Refine top to be positive above, and reuse information in %)
if(top %17 != 3) {
i = 12;
} else {

}
}
__goblint_check(i ==0);
__goblint_check(i ==0); //TODO

i = 0;
if(top % 17 == 0) {
__goblint_check(top%17 == 0);
if(top %17 != 0) {
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6 changes: 3 additions & 3 deletions tests/regression/37-congruence/11-overflow-signed.c
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Expand Up @@ -12,8 +12,8 @@ int basic(){
{
if (b % two_pow_16 == 5)
{
__goblint_check(a % two_pow_16 == 3);
__goblint_check(b % two_pow_16 == 5);
__goblint_check(a % two_pow_16 == 3); //TODO (Refine a to be positive above, and reuse information in %)
__goblint_check(b % two_pow_16 == 5); //TODO (Refine a to be positive above, and reuse information in %)

unsigned int e = a * b;
__goblint_check(e % two_pow_16 == 15); // UNKNOWN!
Expand All @@ -35,7 +35,7 @@ int special(){

if (a % two_pow_18 == two_pow_17)
{
__goblint_check(a % two_pow_18 == two_pow_17);
__goblint_check(a % two_pow_18 == two_pow_17); //TODO (Refine a to be positive above, and reuse information in %)

unsigned int e = a * a;
__goblint_check(e == 0); //UNKNOWN!
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12 changes: 9 additions & 3 deletions tests/regression/37-congruence/13-bitand.c
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Expand Up @@ -5,11 +5,16 @@ int main()
{
// Assuming modulo expression

long x;
unsigned long x;
__goblint_assume(x % 2 == 1);
__goblint_check(x % 2 == 1);
__goblint_check(x & 1);

long xx;
__goblint_assume(xx % 2 == 1);
__goblint_check(xx % 2 == 1); //TODO (Refine xx to be positive above, and reuse information in %)
__goblint_check(xx & 1);

long y;
__goblint_assume(y % 2 == 0);
__goblint_check(y % 2 == 0);
Expand All @@ -27,14 +32,15 @@ int main()
__goblint_check(xz & 1);

// Assuming bitwise expression
// Does NOT actually lead to modulo information, as negative values may also have their last bit set!

long a;
__goblint_assume(a & 1);
__goblint_check(a % 2 == 1);
__goblint_check(a % 2 == 1); //UNKNOWN!
__goblint_check(a & 1);

int b;
__goblint_assume(b & 1);
__goblint_check(b % 2 == 1);
__goblint_check(b % 2 == 1); //UNKNOWN!
__goblint_check(b & 1);
}
15 changes: 15 additions & 0 deletions tests/regression/37-congruence/14-negative.c
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@@ -0,0 +1,15 @@
// PARAM: --enable ana.int.congruence --set sem.int.signed_overflow assume_none
#include <goblint.h>

int main()
{
int top;

int c = -5;
if (top)
{
c = -7;
}
__goblint_check(c % 2 == 1); //UNKNOWN! (Does not hold at runtime)
__goblint_check(c % 2 == -1); //TODO (Track information that c is negative)
}