Before this change, `Expr.isConstant` only was only true for those
constant expressions that could be represented as QL values: numbers,
Booleans, and string literals. It was not true for string literals
converted from arrays to pointers, and it was not true for addresses of
variables with static lifetime.
The concept of a "constant expression" varies between C and C++ and
between versions of the standard, but they all include addresses of data
with static lifetime. These are modelled by the new library
`AddressConstantExpression.qll`, which is based on the code in
`EscapesTree.qll` and modified for its new purpose.
I've tested the change for performance on Wireshark and for correctness
with the included tests. I've also checked on Wireshark that all static
initializers in C files are considered constant, which was not the case
before.
This change suppresses results from "Declaration hides parameter" where
the ParameterDeclarationEntry does not link up to the right
FunctionDeclarationEntry.
Bad magic ended up in `LocalVariable.getFunction` and effectively
created a Cartesian product. Before this change, the timing looked like
this:
Variable::LocalVariable::getFunction_dispred#bb ... 50.1s
#select#cpe#123#fff ............................... 20.6s
After this change, those predicates become much faster:
Variable::LocalVariable::getFunction_dispred#ff ... 121ms
DeclarationHidesParameter::localVariableNames#fff . 77ms
#select#cpe#123#fff ............................... 28ms
Introducing the predicate `localVariableNames` ensures that we can do
the main join on two columns simultaneously, so that's a change we
should keep even if we remove the `pragma[nomagic]` later.
This test was intended to catch regressions in the CFG, but it looks
like it's just catching insignificant extractor changes. The test has
started failing after some recent extractor changes, but I have no way
to pinpoint the failure and understand whether it's a problem or not, so
I think it's better to delete this test.
The remaining tests check whether the QL-based CFG generates the same
graph as the extractor-based CFG. Furthermore, the `successor-tests`
check that the extractor-based CFG works as intended.
