[clang] 627b5c1 - [Sema][SVE] Reject aligned/_Alignas for sizeless types

[Richard Sandiford via cfe-commits]

Author: Richard Sandiford
Date: 2020-03-12T17:12:40Z
New Revision: 627b5c12068cc90b476a9121862a481e1d57be85

URL: https://github.com/llvm/llvm-project/commit/627b5c12068cc90b476a9121862a481e1d57be85
DIFF: https://github.com/llvm/llvm-project/commit/627b5c12068cc90b476a9121862a481e1d57be85.diff

LOG: [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

Added: 
    

Modified: 
    clang/include/clang/Basic/DiagnosticSemaKinds.td
    clang/lib/Sema/SemaDeclAttr.cpp
    clang/test/Sema/sizeless-1.c
    clang/test/SemaCXX/sizeless-1.cpp

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 3a532fedac48..fe0f9e959a1b 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2807,6 +2807,8 @@ def err_alignas_mismatch : Error<
   "redeclaration has 
diff erent 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">;

diff  --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 2e1710f70753..3385717e3138 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -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)

diff  --git a/clang/test/Sema/sizeless-1.c b/clang/test/Sema/sizeless-1.c
index 3f1bfb93a298..3e3c3259681a 100644
--- a/clang/test/Sema/sizeless-1.c
+++ b/clang/test/Sema/sizeless-1.c
@@ -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

diff  --git a/clang/test/SemaCXX/sizeless-1.cpp b/clang/test/SemaCXX/sizeless-1.cpp
index a2ee6205ec97..638eb523ac9c 100644
--- a/clang/test/SemaCXX/sizeless-1.cpp
+++ b/clang/test/SemaCXX/sizeless-1.cpp
@@ -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