The IR generation for `InitializeIndirection` currently connects its load operand to the result of the corresponding `InitializeParameter` instruction. This isn't exactly wrong, but it doesn't fit the IR invariant of "All unmodeled uses consume `UnmodeledDefinition`". Our current code doesn't care, because we just throw away all of the existing def-use information, modeled or otherwise, when we build unaliased SSA. However, some upcoming SSA changes don't work correctly if this invariant is broken.
I've added the trivial IR generation change, along with a new sanity query.
When the extractor can't prove that control flow will never reach the end of a non-`void`-returning function without reaching an explicit `return` statement, it inserts an implicit `return` without an operand. If control actually reaches this point, the behavior is undefined.
We were previously generating invalid IR for these implicit `return` statements, because the lack of an operand meant that there was no definition of the return value variable along that path. Instead, I've changed the IR generation to emit an `Unreached` instruction for the implicit `return`. This ensures that we don't create a control flow edge from the end of the body to the function epilogue.
The change to the range analysis test avoids having that test depend on the previous bad IR behavior, while still preserving the original spirit of the test.
Flow through partial chi-instruction operands was introduced to make
definition-by-reference work, but its implementation also allowed all
other partial writes to propagate. In particular, tainting a field would
taint the whole struct, which in turn led to taint propagating across
unrelated fields of a struct.
The security test `CWE-134/semmle/argv/argvLocal.c` shows that we also
want to propagate taint from an array element to the whole array, and it
also seems right to propagate taint from a union member to the whole
union.
