From: David Majnemer <david.majnemer@gmail.com>
Date: Mon, 20 Jul 2015 22:51:52 +0000 (+0000)
Subject: [MS Compat] Add support for __declspec(noalias)
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=f3e8e6409f7fdf07b2d058dcb797b019ec2595a2;p=clang

[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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@242728 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/clang/Basic/Attr.td b/include/clang/Basic/Attr.td
index fb1eb58dcc..11b3263d70 100644
--- a/include/clang/Basic/Attr.td
+++ b/include/clang/Basic/Attr.td
@@ -867,6 +867,12 @@ def ReturnsTwice : InheritableAttr {
   let Documentation = [Undocumented];
 }
 
+def NoAlias : InheritableAttr {
+  let Spellings = [Declspec<"noalias">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [NoAliasDocs];
+}
+
 def NoCommon : InheritableAttr {
   let Spellings = [GCC<"nocommon">];
   let Subjects = SubjectList<[Var]>;
diff --git a/include/clang/Basic/AttrDocs.td b/include/clang/Basic/AttrDocs.td
index e4ca0cb477..9d7c7662fa 100644
--- a/include/clang/Basic/AttrDocs.td
+++ b/include/clang/Basic/AttrDocs.td
@@ -1583,3 +1583,13 @@ The ``returns_nonnull`` attribute indicates that a particular function (or Objec
 The ``returns_nonnull`` attribute implies that returning a null pointer is undefined behavior, which the optimizer may take advantage of. The ``_Nonnull`` type qualifier indicates that a pointer cannot be null in a more general manner (because it is part of the type system) and does not imply undefined behavior, making it more widely applicable
 }];
 }
+
+def NoAliasDocs : Documentation {
+  let Category = DocCatFunction;
+  let Heading = "noalias";
+  let Content = [{
+The ``noalias`` attribute indicates that the only memory accesses inside
+function are loads and stores from objects pointed to by its pointer-typed
+arguments, with arbitrary offsets.
+  }];
+}
diff --git a/lib/CodeGen/CGCall.cpp b/lib/CodeGen/CGCall.cpp
index 2dc94d06f3..a61f13fb9a 100644
--- a/lib/CodeGen/CGCall.cpp
+++ b/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/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 191dbd05c9..9ec3356d04 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/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;
diff --git a/test/CodeGen/ms-declspecs.c b/test/CodeGen/ms-declspecs.c
index c32733e65f..d5071ab60c 100644
--- a/test/CodeGen/ms-declspecs.c
+++ b/test/CodeGen/ms-declspecs.c
@@ -33,7 +33,12 @@ __declspec(noinline) void t2() {}
 __declspec(noreturn) void f20_t(void);
 void f20(void) { f20_t(); }
 
+__declspec(noalias) void noalias_callee(int *x);
+// CHECK: call void @noalias_callee({{.*}}) [[NA:#[0-9]+]]
+void noalias_caller(int *x) { noalias_callee(x); }
+
 // CHECK: attributes [[NAKED]] = { naked noinline nounwind{{.*}} }
 // CHECK: attributes [[NUW]] = { nounwind{{.*}} }
 // CHECK: attributes [[NI]] = { noinline nounwind{{.*}} }
 // CHECK: attributes [[NR]] = { noreturn }
+// CHECK: attributes [[NA]] = { nounwind argmemonly{{.*}} }
diff --git a/test/Parser/MicrosoftExtensions.c b/test/Parser/MicrosoftExtensions.c
index a29f6c0b54..e58a7455c0 100644
--- a/test/Parser/MicrosoftExtensions.c
+++ b/test/Parser/MicrosoftExtensions.c
@@ -5,7 +5,7 @@ typedef int (__cdecl *tptr)(void);
 void (*__fastcall fastpfunc)(void);
 extern __declspec(dllimport) void __stdcall VarR4FromDec(void);
 __declspec(deprecated) __declspec(deprecated) char * __cdecl ltoa( long _Val, char * _DstBuf, int _Radix);
-__declspec(safebuffers) __declspec(noalias) __declspec(restrict) void * __cdecl xxx(void *_Memory); /* expected-warning{{__declspec attribute 'safebuffers' is not supported}} expected-warning{{__declspec attribute 'noalias' is not supported}} */
+__declspec(safebuffers) __declspec(noalias) __declspec(restrict) void * __cdecl xxx(void *_Memory); /* expected-warning{{__declspec attribute 'safebuffers' is not supported}} */
 typedef __w64 unsigned long ULONG_PTR, *PULONG_PTR;
 
 void * __ptr64 PtrToPtr64(const void *p) {