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Fix remaining clang warnings for fallthrough switch cases (in debug build). (#10314)

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https://github.com/Z3Prover/z3/pull/10284 changed the UNREACHABLE macro
in debug.h to use __builtin_unreachable() to indicate to the compiler
that the
code leading it should be considered unreachable.

In https://github.com/Z3Prover/z3/pull/10295 Copilot figured out that
this was wrong: the unreachable macro makes calls, which shouldn't be
elided, and whose arguments should be evaluated. It partially fixed the
problem by declaring invoke_exit_action to be `[[noreturn]]`. This
eliminated warnings in non-debug builds, but when Z3_DEBUG is enabled,
`UNREACHABLE` ends with an invocation of `INVOKE_DEBUGER()`. This can
call `invoke_debugger()`, which *can* actually return (so it can't be
given the `[[noreturn]]` attribute. So we still get warnings in debug
builds.

This PR fixes those, creating a Z3_unreachable_case macro, which is just
a combination of `UNREACHABLE()` and `Z3_fallthrough`. It uses that in
the places that give warnings.

It seemed better to me to still have these cases have a single macro,
rather than `UNREACHABLE` followed by an explicit `Z3_fallthrough`; this
seemed to me like it would confuse people -- "how can you fall through
if this code is unreachable?" But I'm open to alternative suggestions!
This commit is contained in:
davedets 2026-07-30 19:24:46 -07:00 • committed by GitHub
parent 141e99ffe7
commit c49eb07c3e
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6 changed files with 11 additions and 5 deletions
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2
src/util/sexpr.cpp
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@ -123,7 +123,7 @@ sexpr * const * sexpr::get_children() const {
void sexpr::display_atom(std::ostream & out) const {
switch (get_kind()) {
case sexpr::kind_t::COMPOSITE:
UNREACHABLE();
Z3_unreachable_case();
case sexpr::kind_t::NUMERAL:
out << static_cast<sexpr_numeral const *>(this)->m_val;
break;

6
src/util/util.h
View file

@ -80,6 +80,12 @@ static_assert(sizeof(int64_t) == 8, "64 bits");
# define Z3_fallthrough
#endif
// UNREACHABLE is not defined in a way that makes it clear to the compiler
// that it does not return (because it calls INVOKE_DEBUGGER() in debug builds,
// and that *may* return). Using this for unreachable switch cases avoids
// any fall-through warnings.
#define Z3_unreachable_case() UNREACHABLE(); Z3_fallthrough
static inline bool is_power_of_two(unsigned v) { return !(v & (v - 1)) && v; }
/**