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[clang] Reject VLAs in __is_layout_compatible() #87737

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Merged
merged 2 commits into from
Apr 6, 2024
Merged

[clang] Reject VLAs in __is_layout_compatible() #87737

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ef24f64
[clang] Reject VLAs in `__is_layout_compatible()`
Endilll Apr 5, 2024
a8c24fb
Improve diagnostic wording
Endilll Apr 5, 2024
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2 changes: 1 addition & 1 deletion clang/include/clang/Basic/DiagnosticSemaKinds.td
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Original file line number Diff line number Diff line change
Expand Up @@ -165,7 +165,7 @@ def ext_vla_folded_to_constant : ExtWarn<
"variable length array folded to constant array as an extension">,
InGroup<GNUFoldingConstant>;
def err_vla_unsupported : Error<
"variable length arrays are not supported for %select{the current target|'%1'}0">;
"variable length arrays are not supported %select{for the current target|in '%1'}0">;
def err_vla_in_coroutine_unsupported : Error<
"variable length arrays in a coroutine are not supported">;
def note_vla_unsupported : Note<
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3 changes: 3 additions & 0 deletions clang/lib/Sema/SemaExprCXX.cpp
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Expand Up @@ -6026,6 +6026,9 @@ static bool EvaluateBinaryTypeTrait(Sema &Self, TypeTrait BTT, QualType LhsT,
return false;
}
case BTT_IsLayoutCompatible: {
if (LhsT->isVariableArrayType() || RhsT->isVariableArrayType())
Self.Diag(KeyLoc, diag::err_vla_unsupported)
<< 1 << tok::kw___is_layout_compatible;
return Self.IsLayoutCompatible(LhsT, RhsT);
}
default: llvm_unreachable("not a BTT");
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10 changes: 6 additions & 4 deletions clang/test/SemaCXX/type-traits.cpp
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Expand Up @@ -740,7 +740,7 @@ void is_bounded_array(int n) {
static_assert(!__is_bounded_array(cvoid *));

int t32[n];
(void)__is_bounded_array(decltype(t32)); // expected-error{{variable length arrays are not supported for '__is_bounded_array'}}
(void)__is_bounded_array(decltype(t32)); // expected-error{{variable length arrays are not supported in '__is_bounded_array'}}
}

void is_unbounded_array(int n) {
Expand Down Expand Up @@ -772,7 +772,7 @@ void is_unbounded_array(int n) {
static_assert(!__is_unbounded_array(cvoid *));

int t32[n];
(void)__is_unbounded_array(decltype(t32)); // expected-error{{variable length arrays are not supported for '__is_unbounded_array'}}
(void)__is_unbounded_array(decltype(t32)); // expected-error{{variable length arrays are not supported in '__is_unbounded_array'}}
}

void is_referenceable() {
Expand Down Expand Up @@ -1741,8 +1741,10 @@ void is_layout_compatible(int n)
static_assert(!__is_layout_compatible(unsigned char, signed char));
static_assert(__is_layout_compatible(int[], int[]));
static_assert(__is_layout_compatible(int[2], int[2]));
static_assert(!__is_layout_compatible(int[n], int[2])); // FIXME: VLAs should be rejected
static_assert(!__is_layout_compatible(int[n], int[n])); // FIXME: VLAs should be rejected
static_assert(!__is_layout_compatible(int[n], int[2]));
// expected-error@-1 {{variable length arrays are not supported in '__is_layout_compatible'}}
static_assert(!__is_layout_compatible(int[n], int[n]));
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I think where we ended up is:

  1. Reject incomplete types (still needs to be done)
  2. Reject VLAs (done, looks good)
  3. FAMs are accepted (no changes needed)

So I think you should implement #1 and add tests for it, then add tests for #3, and I think that finishes this.

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I recognize that discussion has spiraled out of VLAs into incomplete types and flexible array members, but can I keep the original scope of this PR, focusing on just VLAs?

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I'm fine with splitting the work across multiple patches so long as we get to the desired end state (or have issues filed to track what that end state should be).

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Yes, other items will be addressed in subsequent PRs.

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I think focusing on VLAs here is fine, that was the original scope and I don't see an urgent need to expand it here.

// expected-error@-1 {{variable length arrays are not supported in '__is_layout_compatible'}}
static_assert(__is_layout_compatible(int&, int&));
static_assert(!__is_layout_compatible(int&, char&));
static_assert(__is_layout_compatible(void(int), void(int)));
Expand Down