[PowerPC][AIX] attribute aligned cannot decrease align of a vector var.

[sfertile]

Summary

On AIX an aligned attribute cannot decrease the alignment of a variable when placed on a variable declaration of vector type.

[aaron.ballman]

clang/lib/Sema/SemaDeclAttr.cpp

4066–4071

4079

4084

This should produce a diagnostic rather than silently drop the attribute. I'd recommend err_alignas_underaligned if you're willing to make this an error. If not, you could add a new warning with the same wording.

[sfertile]

• Fixed spelling mistake
• Check that VD is non-nulll earlier.
• added warning that the requested alignment is too small.
• renamed test

[sfertile]

clang/lib/Sema/SemaDeclAttr.cpp

4084

Thanks for the feedback Aaron. I think an error is too drastic a difference from the other compilers on AIX so I added the warning.

[aaron.ballman]

LGTM aside from a minor nit.

clang/include/clang/Basic/DiagnosticSemaKinds.td

2989–2990

clang/include/clang/Basic/DiagnosticSemaKinds.td

def err_alignas_attribute_wrong_decl_type : Error<
   "variable with 'register' storage class|'catch' variable|bit-field}1">;
 def err_alignas_missing_on_definition : Error<
   "%0 must be specified on definition if it is specified on any declaration">;
 def note_alignas_on_declaration : Note<"declared with %0 attribute here">;
 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 warn_aligned_attr_underaligned : Warning<err_alignas_underaligned.Text>,
+  InGroup<IgnoredAttributes>;
 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|a constant expression}2">;
 def err_attribute_argument_type : Error<
   "%0 attribute requires %select{int or bool|an integer "
   "constant|a string|an identifier}1">;

clang/lib/Sema/SemaDeclAttr.cpp

else if (Context.getTargetInfo().getTriple().isOSAIX())
     MaximumAlignment = std::min(MaximumAlignment, 4096u);
 
   if (AlignVal > MaximumAlignment) {
     Diag(AttrLoc, diag::err_attribute_aligned_too_great)
         << MaximumAlignment << E->getSourceRange();
     return;
   }
 
-  if (Context.getTargetInfo().isTLSSupported()) {
+  const auto *VD = dyn_cast<VarDecl>(D);
+  if (VD && Context.getTargetInfo().isTLSSupported()) {
     unsigned MaxTLSAlign =
         Context.toCharUnitsFromBits(Context.getTargetInfo().getMaxTLSAlign())
             .getQuantity();
-    const auto *VD = dyn_cast<VarDecl>(D);
-    if (MaxTLSAlign && AlignVal > MaxTLSAlign && VD &&
+    if (MaxTLSAlign && AlignVal > MaxTLSAlign &&
         VD->getTLSKind() != VarDecl::TLS_None) {
       Diag(VD->getLocation(), diag::err_tls_var_aligned_over_maximum)
           << (unsigned)AlignVal << VD << MaxTLSAlign;
       return;
     }
   }
 
+  // On AIX, an aligned attribute can not decrease the alignment when applied
+  // to a variable declaration with vector type.
+  if (VD && Context.getTargetInfo().getTriple().isOSAIX()) {
+    const Type *Ty = VD->getType().getTypePtr();
+    if (Ty->isVectorType() && AlignVal < 16) {
+      Diag(VD->getLocation(), diag::warn_aligned_attr_underaligned)
+          << VD->getType() << 16;
+      return;
+    }
+  }
+
   AlignedAttr *AA = ::new (Context) AlignedAttr(Context, CI, true, ICE.get());
   AA->setPackExpansion(IsPackExpansion);
   D->addAttr(AA);
 }
 
 void Sema::AddAlignedAttr(Decl *D, const AttributeCommonInfo &CI,
                           TypeSourceInfo *TS, bool IsPackExpansion) {
   // FIXME: Cache the number on the AL object if non-dependent?

clang/test/CodeGen/aix-vector-attr-aligned.c

+// REQUIRES: powerpc-registered-target
+// RUN: %clang_cc1 -triple powerpc-unknown-aix -target-feature +altivec -target-cpu pwr7 -emit-llvm -o - %s | \
+// RUN:   FileCheck %s
+// RUN: %clang_cc1 -triple powerpc64-unknown-aix -target-feature +altivec -target-cpu pwr7 -emit-llvm -o - %s | \
+// RUN:   FileCheck %s
+
+typedef vector int __attribute__((aligned(8))) UnderAlignedVI;
+
+vector int g32 __attribute__((aligned(32)));
+vector int g8 __attribute__((aligned(8)));
+UnderAlignedVI TypedefedGlobal;
+
+int escape(vector int*);
+
+int local32(void) {
+  vector int l32 __attribute__((aligned(32)));
+  return escape(&l32);
+}
+
+int local8(void) {
+  vector int l8 __attribute__((aligned(8)));
+  return escape(&l8);
+}
+
+// CHECK: @g32 = global <4 x i32> zeroinitializer, align 32
+// CHECK: @g8 = global <4 x i32> zeroinitializer, align 16
+// CHECK: @TypedefedGlobal = global <4 x i32> zeroinitializer, align 8
+
+// CHECK-LABEL: @local32
+// CHECK:         %l32 = alloca <4 x i32>, align 32
+//
+// CHECK-LABEL: @local8
+// CHECK:         %l8 = alloca <4 x i32>, align 16

clang/test/Sema/aix-attr-aligned-vector-warn.c

+// RUN: %clang_cc1 -triple powerpc64-unknown-aix -target-feature +altivec -target-cpu pwr7 -verify -fsyntax-only %s
+// RUN: %clang_cc1 -triple powerpc-unknown-aix -target-feature +altivec -target-cpu pwr7 -verify -fsyntax-only %s
+
+int escape(vector int*);
+
+typedef vector int __attribute__((aligned(8))) UnderAlignedVI;
+UnderAlignedVI TypedefedGlobal;
+
+vector int V __attribute__((aligned(8))); // expected-warning {{requested alignment is less than minimum alignment of 16 for type '__vector int' (vector of 4 'int' values)}}
+
+int localTypedefed(void) {
+  UnderAlignedVI TypedefedLocal;
+  return escape(&TypedefedLocal); // expected-warning {{passing 8-byte aligned argument to 16-byte aligned parameter 1 of 'escape' may result in an unaligned pointer access}}
+}