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Merge pull request diffblue#2125 from smowton/smowton/feature/symex-ignore-null-derefs
Symex: ignore null dereferences when targeting Java
2 parents 001fca0 + 9fd3434 commit 0784f77

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20 files changed

+651
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‎jbmc/regression/jbmc/symex_should_exclude_null_pointers/test.class

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‎jbmc/regression/jbmc/symex_should_exclude_null_pointers/test.desc

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CORE
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test.class
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--function test.main
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^EXIT=10$
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^SIGNAL=0$
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^VERIFICATION FAILED$
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Null pointer check: FAILURE$
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assertion at file test\.java line 21 .*: SUCCESS$
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--
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^warning: ignoring
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--
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JBMC should reports failure, as it might dereference a null pointer, but as Java
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is a safe language we should statically determine that if we reach the assertion
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it cannot be violated.

‎jbmc/regression/jbmc/symex_should_exclude_null_pointers/test.java

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public class test {
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public int field;
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public test(int value) {
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field = value;
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}
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public static void main(boolean unknown) {
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test t = new test(12345);
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test maybe_t = unknown ? null : t;
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// t could still be null, but symex ought to notice that as the Java frontend introduces
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// checks before all pointer dereference operations, it can statically eliminate
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// the assertion below.
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int field_value = maybe_t.field;
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assert field_value == 12345;
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}
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}

‎jbmc/regression/jbmc/symex_should_exclude_null_pointers/test_vccs.desc

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CORE
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test.class
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--show-vcc --function test.main
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^EXIT=0$
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^SIGNAL=0$
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--
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^warning: ignoring
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assertion at file test\.java line 22
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--
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Because symex should statically determine the assertion can't be violated there should not be a goal for it
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by the time --show-vccs prints the equation.

‎regression/cbmc/symex_should_exclude_null_pointers/main.c

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static void noop() { }
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int main(int argc, char **argv) {
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int x;
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int *maybe_null = argc & 1 ? &x : 0;
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// Should work (guarded by assume):
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int *ptr1 = maybe_null;
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__CPROVER_assume(ptr1 != 0);
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int deref1 = *ptr1;
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// Should work (guarded by else):
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int *ptr2 = maybe_null;
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if(ptr2 == 0)
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{
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}
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else
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{
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int deref2 = *ptr2;
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}
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// Should work (guarded by if):
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int *ptr3 = maybe_null;
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if(ptr3 != 0)
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{
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int deref3 = *ptr3;
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}
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// Shouldn't work yet despite being safe (guarded by backward goto):
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int *ptr4 = maybe_null;
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goto check;
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deref:
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int deref4 = *ptr4;
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goto end_test4;
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check:
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__CPROVER_assume(ptr4 != 0);
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goto deref;
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end_test4:
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// Shouldn't work yet despite being safe (guarded by confluence):
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int *ptr5 = maybe_null;
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if(argc == 5)
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__CPROVER_assume(ptr5 != 0);
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else
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__CPROVER_assume(ptr5 != 0);
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int deref5 = *ptr5;
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// Shouldn't work (unsafe as only guarded on one branch):
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int *ptr6 = maybe_null;
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if(argc == 6)
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__CPROVER_assume(ptr6 != 0);
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else
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{
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}
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int deref6 = *ptr6;
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// Shouldn't work due to suspicion write to ptr6 might alter ptr7:
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int *ptr7 = maybe_null;
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__CPROVER_assume(ptr7 != 0);
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ptr6 = 0;
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int deref7 = *ptr7;
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// Shouldn't work due to suspicion noop() call might alter ptr8:
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int *ptr8 = maybe_null;
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__CPROVER_assume(ptr8 != 0);
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noop();
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int deref8 = *ptr8;
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assert(0);
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}

‎regression/cbmc/symex_should_exclude_null_pointers/test.desc

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CORE
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main.c
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--show-vcc
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^EXIT=0$
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^SIGNAL=0$
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ptr4\$object
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ptr5\$object
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ptr6\$object
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ptr7\$object
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ptr8\$object
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--
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ptr[1-3]\$object
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^warning: ignoring
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--
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ptrX\$object appearing in the VCCs indicates symex was unsure whether the pointer had a valid
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target, and uses the $object symbol as a referred object of last resort. ptr1-3 should be judged
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not-null by symex, so their $object symbols do not occur.

‎regression/goto-instrument/safe-dereferences/main.c

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static void noop() { }
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int main(int argc, char **argv) {
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int x;
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// Should work (guarded by assume):
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int *ptr1 = &x;
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__CPROVER_assume(ptr1 != 0);
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int deref1 = *ptr1;
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// Should work (guarded by else):
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int *ptr2 = &x;
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if(ptr2 == 0)
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{
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}
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else
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{
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int deref2 = *ptr2;
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}
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// Should work (guarded by if):
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int *ptr3 = &x;
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if(ptr3 != 0)
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{
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int deref3 = *ptr3;
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}
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// Shouldn't work yet despite being safe (guarded by backward goto):
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int *ptr4 = &x;
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goto check;
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deref:
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int deref4 = *ptr4;
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goto end_test4;
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check:
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__CPROVER_assume(ptr4 != 0);
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goto deref;
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end_test4:
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// Shouldn't work yet despite being safe (guarded by confluence):
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int *ptr5 = &x;
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if(argc == 5)
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__CPROVER_assume(ptr5 != 0);
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else
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__CPROVER_assume(ptr5 != 0);
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int deref5 = *ptr5;
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// Shouldn't work (unsafe as only guarded on one branch):
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int *ptr6 = &x;
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if(argc == 6)
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__CPROVER_assume(ptr6 != 0);
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else
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{
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}
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int deref6 = *ptr6;
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// Shouldn't work due to suspicion *ptr6 might alter ptr7:
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int *ptr7 = &x;
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__CPROVER_assume(ptr7 != 0);
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ptr6 = 0;
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int deref7 = *ptr7;
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// Shouldn't work due to suspicion noop() call might alter ptr8:
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int *ptr8 = &x;
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__CPROVER_assume(ptr8 != 0);
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noop();
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int deref8 = *ptr8;
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}

‎regression/goto-instrument/safe-dereferences/test.desc

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CORE
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main.c
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--show-safe-dereferences
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^EXIT=0$
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^SIGNAL=0$
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Safe \(known-not-null\) dereferences: \{main::[0-9]+::ptr1\}
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Safe \(known-not-null\) dereferences: \{main::[0-9]+::ptr2\}
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Safe \(known-not-null\) dereferences: \{main::[0-9]+::ptr3\}
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--
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Safe \(known-not-null\) dereferences: \{main::[0-9]+::ptr[4-8]\}
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^warning: ignoring
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--
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See comments in main.c for details about what each ptr variable is testing, and why they
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should or shouldn't be seen as safe accesses.

‎src/analyses/Makefile

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@@ -20,6 +20,7 @@ SRC = ai.cpp \
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local_bitvector_analysis.cpp \
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local_cfg.cpp \
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local_may_alias.cpp \
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local_safe_pointers.cpp \
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locals.cpp \
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natural_loops.cpp \
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reaching_definitions.cpp \

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