[MS Compat] Add support for __declspec(noalias)

The attribute '__declspec(noalias)' communicates that the function only
accesses memory pointed to by its pointer-typed arguments.

llvm-svn: 242728

2 files changed, 7 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 2dc94d06f32..a61f13fb9ab 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -1421,13 +1421,16 @@ void CodeGenModule::ConstructAttributeList(const CGFunctionInfo &FI,
         FuncAttrs.addAttribute(llvm::Attribute::NoReturn);
     }
 
-    // 'const' and 'pure' attribute functions are also nounwind.
+    // 'const', 'pure' and 'noalias' attributed functions are also nounwind.
     if (TargetDecl->hasAttr<ConstAttr>()) {
       FuncAttrs.addAttribute(llvm::Attribute::ReadNone);
       FuncAttrs.addAttribute(llvm::Attribute::NoUnwind);
     } else if (TargetDecl->hasAttr<PureAttr>()) {
       FuncAttrs.addAttribute(llvm::Attribute::ReadOnly);
       FuncAttrs.addAttribute(llvm::Attribute::NoUnwind);
+    } else if (TargetDecl->hasAttr<NoAliasAttr>()) {
+      FuncAttrs.addAttribute(llvm::Attribute::ArgMemOnly);
+      FuncAttrs.addAttribute(llvm::Attribute::NoUnwind);
     }
     if (TargetDecl->hasAttr<RestrictAttr>())
       RetAttrs.addAttribute(llvm::Attribute::NoAlias);
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 191dbd05c9b..9ec3356d048 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -4723,6 +4723,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_Mode:
     handleModeAttr(S, D, Attr);
     break;
+  case AttributeList::AT_NoAlias:
+    handleSimpleAttribute<NoAliasAttr>(S, D, Attr);
+    break;
   case AttributeList::AT_NoCommon:
     handleSimpleAttribute<NoCommonAttr>(S, D, Attr);
     break;