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[Sema][SVE] Reject aligned/_Alignas for sizeless types 

A previous patch rejected alignof for sizeless types.  This patch
extends that to cover the "aligned" attribute and _Alignas.  Since
sizeless types are not meant to be used for long-term data, cannot
be used in aggregates, and cannot have static storage duration,
there shouldn't be any need to fiddle with their alignment.

Like with alignof, this is a conservative position that can be
relaxed in future if it turns out to be too restrictive.

Differential Revision: https://reviews.llvm.org/D75573
This commit is contained in:
Richard Sandiford 2020-03-02 17:37:58 +00:00
parent 39969c7d3a
commit 627b5c1206
4 changed files with 16 additions and 1 deletions
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2
clang/include/clang/Basic/DiagnosticSemaKinds.td
View File

@ -2807,6 +2807,8 @@ def err_alignas_mismatch : Error<
"redeclaration has different alignment requirement (%1 vs %0)">;
def err_alignas_underaligned : Error<
"requested alignment is less than minimum alignment of %1 for type %0">;
def err_attribute_sizeless_type : Error<
"%0 attribute cannot be applied to sizeless type %1">;
def err_attribute_argument_n_type : Error<
"%0 attribute requires parameter %1 to be %select{int or bool|an integer "
"constant|a string|an identifier}2">;

7
clang/lib/Sema/SemaDeclAttr.cpp
View File

@ -3868,6 +3868,7 @@ void Sema::CheckAlignasUnderalignment(Decl *D) {
// not specify an alignment that is less strict than the alignment that
// would otherwise be required for the entity being declared.
AlignedAttr *AlignasAttr = nullptr;
AlignedAttr *LastAlignedAttr = nullptr;
unsigned Align = 0;
for (auto *I : D->specific_attrs<AlignedAttr>()) {
if (I->isAlignmentDependent())
@ -3875,9 +3876,13 @@ void Sema::CheckAlignasUnderalignment(Decl *D) {
if (I->isAlignas())
AlignasAttr = I;
Align = std::max(Align, I->getAlignment(Context));
LastAlignedAttr = I;
}
if (AlignasAttr && Align) {
if (Align && DiagTy->isSizelessType()) {
Diag(LastAlignedAttr->getLocation(), diag::err_attribute_sizeless_type)
<< LastAlignedAttr << DiagTy;
} else if (AlignasAttr && Align) {
CharUnits RequestedAlign = Context.toCharUnitsFromBits(Align);
CharUnits NaturalAlign = Context.getTypeAlignInChars(UnderlyingTy);
if (NaturalAlign > RequestedAlign)

4
clang/test/Sema/sizeless-1.c
View File

@ -51,6 +51,10 @@ void func(int sel) {
svint8_t local_int8;
svint16_t local_int16;
svint8_t __attribute__((aligned)) aligned_int8_1; // expected-error {{'aligned' attribute cannot be applied to sizeless type 'svint8_t'}}
svint8_t __attribute__((aligned(4))) aligned_int8_2; // expected-error {{'aligned' attribute cannot be applied to sizeless type 'svint8_t'}}
svint8_t _Alignas(int) aligned_int8_3; // expected-error {{'_Alignas' attribute cannot be applied to sizeless type 'svint8_t'}}
int _Alignas(svint8_t) aligned_int; // expected-error {{invalid application of 'alignof' to sizeless type 'svint8_t'}}
// Using pointers to sizeless data isn't wrong here, but because the

4
clang/test/SemaCXX/sizeless-1.cpp
View File

@ -61,6 +61,10 @@ void func(int sel) {
svint8_t local_int8;
svint16_t local_int16;
svint8_t __attribute__((aligned)) aligned_int8_1; // expected-error {{'aligned' attribute cannot be applied to sizeless type 'svint8_t'}}
svint8_t __attribute__((aligned(4))) aligned_int8_2; // expected-error {{'aligned' attribute cannot be applied to sizeless type 'svint8_t'}}
svint8_t _Alignas(int) aligned_int8_3; // expected-error {{'_Alignas' attribute cannot be applied to sizeless type 'svint8_t'}}
int _Alignas(svint8_t) aligned_int; // expected-error {{invalid application of 'alignof' to sizeless type 'svint8_t'}}
// Using pointers to sizeless data isn't wrong here, but because the