[PATCH] D67734: [CLANG-BPF] change __builtin_preserve_access_index() signature

[Yonghong Song via Phabricator via cfe-commits]

yonghong-song created this revision.
yonghong-song added a reviewer: ast.
Herald added subscribers: cfe-commits, arphaman.
Herald added a project: clang.

The clang intrinsic __builtin_preserve_access_index() currently
has signature:

  const void * __builtin_preserve_access_index(const void * ptr)

This may cause compiler warning when:

- parameter type is "volatile void *" or "const volatile void *", or
- the assign-to type of the intrinsic does not have "const" qualifier.

These warnings can be suppressed by type casting in the user code.
But let's design the __builtin_preserve_access_index() to be more
user friendly to avoid user casting.

The new signature looks like:

  void * __builtin_preserve_access_index(const volatile void * ptr)

A type casting is generated to "void *" at the end of builtin
codegen. This type casting is typically combined with other subsequent
user casts or optimized away completely and has little impact on
optimized IR.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D67734

Files:
  clang/docs/LanguageExtensions.rst
  clang/include/clang/Basic/Builtins.def
  clang/lib/CodeGen/CGBuiltin.cpp
  clang/lib/Sema/SemaChecking.cpp
  clang/test/Sema/builtin-preserve-access-index.c


Index: clang/test/Sema/builtin-preserve-access-index.c
===================================================================
--- clang/test/Sema/builtin-preserve-access-index.c
+++ clang/test/Sema/builtin-preserve-access-index.c
@@ -4,10 +4,10 @@
   return __builtin_preserve_access_index(&arg[1], 1); // expected-error {{too many arguments to function call, expected 1, have 2}}
 }
 
-void *invalid2(const int *arg) {
-  return __builtin_preserve_access_index(&arg[1]); // expected-warning {{returning 'const void *' from a function with result type 'void *' discards qualifiers}}
+void *valid2(const int *arg) {
+  return __builtin_preserve_access_index(&arg[1]);
 }
 
 const void *invalid3(const int *arg) {
-  return __builtin_preserve_access_index(1); // expected-warning {{incompatible integer to pointer conversion passing 'int' to parameter of type 'const void *'}}
+  return __builtin_preserve_access_index(1); // expected-warning {{incompatible integer to pointer conversion passing 'int' to parameter of type 'const volatile void *'}}
 }
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -197,7 +197,6 @@
   if (checkArgCount(S, TheCall, 1))
     return true;
 
-  TheCall->setType(TheCall->getArg(0)->getType());
   return false;
 }
 
Index: clang/lib/CodeGen/CGBuiltin.cpp
===================================================================
--- clang/lib/CodeGen/CGBuiltin.cpp
+++ clang/lib/CodeGen/CGBuiltin.cpp
@@ -1879,6 +1879,8 @@
 
     IsInPreservedAIRegion = true;
     Value *Res = EmitScalarExpr(E->getArg(0));
+    unsigned AddrSpace = Res->getType()->getPointerAddressSpace();
+    Res = Builder.CreateBitCast(Res, Int8Ty->getPointerTo(AddrSpace));
     IsInPreservedAIRegion = false;
     return RValue::get(Res);
   }
Index: clang/include/clang/Basic/Builtins.def
===================================================================
--- clang/include/clang/Basic/Builtins.def
+++ clang/include/clang/Basic/Builtins.def
@@ -1470,7 +1470,7 @@
 BUILTIN(__builtin_operator_delete, "vv*", "tn")
 BUILTIN(__builtin_char_memchr, "c*cC*iz", "n")
 BUILTIN(__builtin_dump_struct, "ivC*v*", "tn")
-BUILTIN(__builtin_preserve_access_index, "vC*vC*", "nU")
+BUILTIN(__builtin_preserve_access_index, "v*vCD*", "nU")
 
 // Safestack builtins
 BUILTIN(__builtin___get_unsafe_stack_start, "v*", "Fn")
Index: clang/docs/LanguageExtensions.rst
===================================================================
--- clang/docs/LanguageExtensions.rst
+++ clang/docs/LanguageExtensions.rst
@@ -2358,7 +2358,7 @@
 
 .. code-block:: c
 
-  const void * __builtin_preserve_access_index(const void * ptr)
+  void * __builtin_preserve_access_index(const volatile void * ptr)
 
 **Example of Use**:
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D67734.220750.patch
Type: text/x-patch
Size: 2829 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20190918/8d74ac88/attachment.bin>