[clang] New __attribute__((__clang_arm_mve_alias)).

This allows you to declare a function with a name of your choice (say
`foo`), but have clang treat it as if it were a builtin function (say
`__builtin_foo`), by writing

  static __inline__ __attribute__((__clang_arm_mve_alias(__builtin_foo)))
  int foo(args);

I'm intending to use this for the ACLE intrinsics for MVE, which have
to be polymorphic on their argument types and also need to be
implemented by builtins. To avoid having to implement the polymorphism
with several layers of nested _Generic and make error reporting
hideous, I want to make all the user-facing intrinsics correspond
directly to clang builtins, so that after clang resolves
__attribute__((overloadable)) polymorphism it's already holding the
right BuiltinID for the intrinsic it selected.

However, this commit itself just introduces the new attribute, and
doesn't use it for anything.

To avoid unanticipated side effects if this attribute is used to make
aliases to other builtins, there's a restriction mechanism: only
(BuiltinID, alias) pairs that are approved by the function
ArmMveAliasValid() will be permitted. At present, that function
doesn't permit anything, because the Tablegen that will generate its
list of valid pairs isn't yet implemented. So the only test of this
facility is one that checks that an unapproved builtin _can't_ be
aliased.

Reviewers: dmgreen, miyuki, ostannard

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67159

1 files changed, 29 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index b2be6245a81..cebb1c642b9 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -23,6 +23,7 @@
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Basic/TargetBuiltins.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Sema/DeclSpec.h"
@@ -4830,6 +4831,30 @@ static void handleXRayLogArgsAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
                  XRayLogArgsAttr(S.Context, AL, ArgCount.getSourceIndex()));
 }
 
+static bool ArmMveAliasValid(unsigned BuiltinID, StringRef AliasName) {
+  // FIXME: this will be filled in by Tablegen which isn't written yet
+  return false;
+}
+
+static void handleArmMveAliasAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  if (!AL.isArgIdent(0)) {
+    S.Diag(AL.getLoc(), diag::err_attribute_argument_n_type)
+        << AL << 1 << AANT_ArgumentIdentifier;
+    return;
+  }
+
+  IdentifierInfo *Ident = AL.getArgAsIdent(0)->Ident;
+  unsigned BuiltinID = Ident->getBuiltinID();
+
+  if (!ArmMveAliasValid(BuiltinID,
+                        cast<FunctionDecl>(D)->getIdentifier()->getName())) {
+    S.Diag(AL.getLoc(), diag::err_attribute_arm_mve_alias);
+    return;
+  }
+
+  D->addAttr(::new (S.Context) ArmMveAliasAttr(S.Context, AL, Ident));
+}
+
 //===----------------------------------------------------------------------===//
 // Checker-specific attribute handlers.
 //===----------------------------------------------------------------------===//
@@ -7160,6 +7185,10 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_MSAllocator:
     handleMSAllocatorAttr(S, D, AL);
     break;
+
+  case ParsedAttr::AT_ArmMveAlias:
+    handleArmMveAliasAttr(S, D, AL);
+    break;
   }
 }