Skip to content

C++: Store destinations should not be uses for dataflow SSA #7578

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 3 commits into from
Jan 18, 2022
Merged

C++: Store destinations should not be uses for dataflow SSA #7578

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
e8afec4
C++: Add testcase that demonstrates a FP caused by spurious flow thro…
MathiasVP Jan 14, 2022
25253c7
C++: Don't count write operations as uses for IR dataflow. Accept tes…
MathiasVP Jan 14, 2022
e1598ab
C++: Fix spelling.
MathiasVP Jan 18, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
14 changes: 10 additions & 4 deletions cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaInternals.qll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -170,10 +170,16 @@ private class ReturnParameterIndirection extends Use, TReturnParamIndirection {
}

private predicate isExplicitUse(Operand op) {
op.getDef() instanceof VariableAddressInstruction and
not exists(LoadInstruction load |
load.getSourceAddressOperand() = op and
load.getAUse().getUse() instanceof InitializeIndirectionInstruction
exists(VariableAddressInstruction vai | vai = op.getDef() |
// Don't include this operand as a use if it only exists to initialize the
// indirection of a parameter.
not exists(LoadInstruction load |
load.getSourceAddressOperand() = op and
load.getAUse().getUse() instanceof InitializeIndirectionInstruction
) and
// Don't include this operand as a use if the only use of the address is for a write
// that definitely overrides a variable.
not (explicitWrite(true, _, vai) and exists(unique( | | vai.getAUse())))
)
}

Expand Down
3 changes: 3 additions & 0 deletions cpp/ql/test/library-tests/dataflow/dataflow-tests/dataflow-ir-consistency.expected
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -570,6 +570,9 @@ postWithInFlow
| test.cpp:481:24:481:30 | FieldAddress [post update] | PostUpdateNode should not be the target of local flow. |
| test.cpp:481:24:481:30 | content [post update] | PostUpdateNode should not be the target of local flow. |
| test.cpp:482:8:482:16 | VariableAddress [post update] | PostUpdateNode should not be the target of local flow. |
| test.cpp:489:7:489:7 | VariableAddress [post update] | PostUpdateNode should not be the target of local flow. |
| test.cpp:491:5:491:5 | x [post update] | PostUpdateNode should not be the target of local flow. |
| test.cpp:494:5:494:5 | x [post update] | PostUpdateNode should not be the target of local flow. |
| true_upon_entry.cpp:9:7:9:7 | VariableAddress [post update] | PostUpdateNode should not be the target of local flow. |
| true_upon_entry.cpp:10:12:10:12 | VariableAddress [post update] | PostUpdateNode should not be the target of local flow. |
| true_upon_entry.cpp:10:27:10:27 | VariableAddress [post update] | PostUpdateNode should not be the target of local flow. |
Expand Down
14 changes: 13 additions & 1 deletion cpp/ql/test/library-tests/dataflow/dataflow-tests/test.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -481,4 +481,16 @@ void local_field_flow_def_by_ref_steps_with_local_flow(MyStruct * s) {
writes_to_content(s->content);
int* p_content = s->content;
sink(*p_content);
}
}

bool unknown();

void regression_with_phi_flow(int clean1) {
int x = 0;
while (unknown()) {
x = clean1;
if (unknown()) { }
sink(x); // clean
x = source();
}
}