3 files changed, 91 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 3db23f2bcb7..b40fa9d93d4 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -1743,6 +1743,25 @@ void CodeGenFunction::EmitFunctionProlog(const CGFunctionInfo &FI,
                                                   AI->getArgNo() + 1,
                                                   llvm::Attribute::NonNull));
           }
+
+          const auto *AVAttr = PVD->getAttr<AlignValueAttr>();
+          if (!AVAttr)
+            if (const auto *TOTy = dyn_cast<TypedefType>(OTy))
+              AVAttr = TOTy->getDecl()->getAttr<AlignValueAttr>();
+          if (AVAttr) {         
+            llvm::Value *AlignmentValue =
+              EmitScalarExpr(AVAttr->getAlignment());
+            llvm::ConstantInt *AlignmentCI =
+              cast<llvm::ConstantInt>(AlignmentValue);
+            unsigned Alignment =
+              std::min((unsigned) AlignmentCI->getZExtValue(),
+                       +llvm::Value::MaximumAlignment);
+
+            llvm::AttrBuilder Attrs;
+            Attrs.addAlignmentAttr(Alignment);
+            AI->addAttr(llvm::AttributeSet::get(getLLVMContext(),
+                                                AI->getArgNo() + 1, Attrs));
+          }
         }
 
         if (Arg->getType().isRestrictQualified())
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 227ceaaee29..406e511651f 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -2757,6 +2757,58 @@ static void handleAnnotateAttr(Sema &S, Decl *D, const AttributeList &Attr) {
                           Attr.getAttributeSpellingListIndex()));
 }
 
+static void handleAlignValueAttr(Sema &S, Decl *D,
+                                 const AttributeList &Attr) {
+  S.AddAlignValueAttr(Attr.getRange(), D, Attr.getArgAsExpr(0),
+                      Attr.getAttributeSpellingListIndex());
+}
+
+void Sema::AddAlignValueAttr(SourceRange AttrRange, Decl *D, Expr *E,
+                             unsigned SpellingListIndex) {
+  AlignValueAttr TmpAttr(AttrRange, Context, E, SpellingListIndex);
+  SourceLocation AttrLoc = AttrRange.getBegin();
+
+  QualType T;
+  if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(D))
+    T = TD->getUnderlyingType();
+  else if (ValueDecl *VD = dyn_cast<ValueDecl>(D))
+    T = VD->getType();
+  else
+    llvm_unreachable("Unknown decl type for align_value");
+
+  if (!T->isDependentType() && !T->isAnyPointerType() &&
+      !T->isReferenceType() && !T->isMemberPointerType()) {
+    Diag(AttrLoc, diag::warn_attribute_pointer_or_reference_only)
+      << &TmpAttr /*TmpAttr.getName()*/ << T << D->getSourceRange();
+    return;
+  }
+
+  if (!E->isValueDependent()) {
+    llvm::APSInt Alignment(32);
+    ExprResult ICE
+      = VerifyIntegerConstantExpression(E, &Alignment,
+          diag::err_align_value_attribute_argument_not_int,
+            /*AllowFold*/ false);
+    if (ICE.isInvalid())
+      return;
+
+    if (!Alignment.isPowerOf2()) {
+      Diag(AttrLoc, diag::err_alignment_not_power_of_two)
+        << E->getSourceRange();
+      return;
+    }
+
+    D->addAttr(::new (Context)
+               AlignValueAttr(AttrRange, Context, ICE.get(),
+               SpellingListIndex));
+    return;
+  }
+
+  // Save dependent expressions in the AST to be instantiated.
+  D->addAttr(::new (Context) AlignValueAttr(TmpAttr));
+  return;
+}
+
 static void handleAlignedAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   // check the attribute arguments.
   if (Attr.getNumArgs() > 1) {
@@ -4181,6 +4233,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_Aligned:
     handleAlignedAttr(S, D, Attr);
     break;
+  case AttributeList::AT_AlignValue:
+    handleAlignValueAttr(S, D, Attr);
+    break;
   case AttributeList::AT_AlwaysInline:
     handleAlwaysInlineAttr(S, D, Attr);
     break;
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 9d194a3ad14..dce8ca4c8a9 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -152,6 +152,17 @@ static void instantiateDependentAssumeAlignedAttr(
                          Aligned->getSpellingListIndex());
 }
 
+static void instantiateDependentAlignValueAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const AlignValueAttr *Aligned, Decl *New) {
+  // The alignment expression is a constant expression.
+  EnterExpressionEvaluationContext Unevaluated(S, Sema::ConstantEvaluated);
+  ExprResult Result = S.SubstExpr(Aligned->getAlignment(), TemplateArgs);
+  if (!Result.isInvalid())
+    S.AddAlignValueAttr(Aligned->getLocation(), New, Result.getAs<Expr>(),
+                        Aligned->getSpellingListIndex());
+}
+
 static void instantiateDependentEnableIfAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const EnableIfAttr *A, const Decl *Tmpl, Decl *New) {
@@ -205,6 +216,12 @@ void Sema::InstantiateAttrs(const MultiLevelTemplateArgumentList &TemplateArgs,
       continue;
     }
 
+    const AlignValueAttr *AlignValue = dyn_cast<AlignValueAttr>(TmplAttr);
+    if (AlignValue) {
+      instantiateDependentAlignValueAttr(*this, TemplateArgs, AlignValue, New);
+      continue;
+    }
+
     const EnableIfAttr *EnableIf = dyn_cast<EnableIfAttr>(TmplAttr);
     if (EnableIf && EnableIf->getCond()->isValueDependent()) {
       instantiateDependentEnableIfAttr(*this, TemplateArgs, EnableIf, Tmpl,