Failed to convert code to internal representation

Vulnerability potential	Low
DDoS potential	None

Failed to convert code to internal representation

Impact

This is an analyzer-internal diagnostic. The source parsed successfully into an AST, but the next stage — lowering that tree into Visao’s intermediate representation (IR) — could not complete. It is not a defect in the analyzed program; it reports that the analyzer’s own model of the code could not be built.

Because the analysis engine reasons over the IR (control-flow graphs, value tracking, the defect checks), a function or translation unit that fails to lower is excluded from analysis. Any real defects in that code are not reported, so the file appears clean only because it was never modelled.

Vulnerability potential

This message has essentially no security meaning for the analyzed code: it is a limitation of the lowering stage, not an exploitable state in the target. The one indirect risk is the familiar coverage gap — code that cannot be lowered is skipped, so a genuine vulnerability there is missed. That keeps the rating at Low rather than None. The diagnostic implies no memory corruption or other unsafe behaviour inside Visao itself.

Technical details

IR lowering walks the type-checked AST and rewrites each construct into a small, uniform set of operations the analysis engine understands. The conversion fails when it meets a construct it has no lowering rule for, or when an invariant the IR builder relies on is violated.

Unsupported constructs

Language or library features the lowering pass does not yet model — inline assembly, computed goto, certain C++ features (coroutines, fold expressions, complex template instantiations), compiler builtins, or vendor intrinsics. The AST is valid but there is no rule to translate it.

Incomplete semantic information

Lowering often needs resolved types and sizes. If a type is incomplete, a sizeof is unresolved, or a symbol could not be linked to a declaration, the builder cannot produce well-formed IR and aborts.

Internal invariant violations

A node shape the builder did not anticipate (an unexpected combination of qualifiers, an empty expression where one was required) can trip an assertion in the lowering pass.

Catching the issue

This is a tool diagnostic; the goal is to let lowering succeed, not to alter program logic.

Isolate the construct

The diagnostic points at the offending function or expression. Reduce it to a minimal snippet that still fails; the failing construct is usually one specific feature.

Provide complete types

Make sure all needed headers and definitions are available so the front-end hands complete, resolved types to the lowering stage; many failures are really missing type information rather than a true gap.

Report and gate

When standard, well-typed code fails to lower, file the minimal reproducer so a lowering rule can be added. In CI, treat lowering failures as errors so the resulting coverage gaps are not silently accepted.

How to reproduce

Give the analyzer valid, parseable code that uses a construct the IR builder does not model, such as inline assembly. The AST builds, but lowering reports a failure to convert the function and the body is left unanalyzed.

int probe_tsc(void)
{
    unsigned lo, hi;

    /* Parses fine, but the IR builder has no lowering rule for the
       inline-asm block and cannot model this function. */
    __asm__ volatile ("rdtsc" : "=a"(lo), "=d"(hi));

    return (int)lo;
}