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[clang] The ms-extension __noop should return zero in a constexpr context. #106849

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Merged
merged 9 commits into from
Sep 2, 2024
Merged

[clang] The ms-extension __noop should return zero in a constexpr context. #106849

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6ce4604
fix cast
c8ef Aug 30, 2024
e946961
Merge branch 'main' into main
c8ef Aug 31, 2024
8b95b33
Merge branch 'main' into main
c8ef Aug 31, 2024
8e7fdb8
Merge branch 'main' into main
c8ef Aug 31, 2024
f0957df
__noop should return 0
c8ef Aug 31, 2024
a53cbbb
Revert "fix cast"
c8ef Aug 31, 2024
a3727d3
__noop should return 0
c8ef Aug 31, 2024
cc6f208
add more test
c8ef Sep 1, 2024
bf2d194
Update clang/lib/AST/ExprConstant.cpp
c8ef Sep 1, 2024
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4 changes: 2 additions & 2 deletions clang/lib/AST/ExprConstant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12720,8 +12720,8 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
}

case Builtin::BI__noop:
// __noop always evaluates successfully
return true;
// __noop always evaluates successfully and returns 0.
return Success(0, E);

case Builtin::BI__builtin_is_constant_evaluated: {
const auto *Callee = Info.CurrentCall->getCallee();
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18 changes: 17 additions & 1 deletion clang/test/SemaCXX/builtins.cpp
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Expand Up @@ -177,5 +177,21 @@ static void __builtin_cpu_init(); // expected-error {{static declaration of '__b
#endif

#ifdef _MSC_VER
constexpr int x = []{ __noop; return 0; }(); // expected-no-diagnostics
constexpr int x = [] {
__noop;
return 0;
}(); // expected-no-diagnostics
static_assert([] { return __noop; }() == 0);
static_assert([] { return __noop(4); }() == 0);
extern int not_accessed;
void not_called();
static_assert([] { return __noop(not_accessed *= 6); }() == 0);
static_assert([] { return __noop(not_called()); }() == 0);
static_assert([] { return __noop(throw ""); }() == 0);
static_assert([] { return __noop(throw "", throw ""); }() == 0);
static_assert([] {
int a = 5;
__noop(++a);
return a;
}() == 5);
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Could you also add tests that calling it returns zero and doesn't evaluate its arguments:

static_assert([]{ return __noop(4); }() == 0);
extern int not_accessed;
void not_called();
static_assert([]{ return __noop(not_accessed *= 6); }() == 0);
static_assert([]{ return __noop(not_called()); }() == 0);
static_assert([]{ return __noop(throw ""); }() == 0);
static_assert([]{ return __noop(throw "", throw ""); }() == 0);
static_assert([]{ int a = 5; __noop(++a); return a; }() == 5);

This passes on MSVC (https://godbolt.org/z/nvxr3GxT4) but currently crashes Clang.

Done.

#endif
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