[PATCH] D54188: [Sema] Mark target of __attribute__((alias("target"))) used for C

[Nick Desaulniers via Phabricator via cfe-commits]

nickdesaulniers created this revision.
nickdesaulniers added a reviewer: rsmith.
Herald added subscribers: cfe-commits, erik.pilkington.

Prevents -Wunneeded-internal-delcaration warnings when the target has no
other references. This occurs frequently in device drivers in the Linux
kernel.

Sema would need to invoke the demangler on the target, since in C++ the
target name is mangled:

int f() { return 42; }
int g() __attribute__((alias("_Z1fv")));

Sema does not have the ability to demangle names at this time.

https://bugs.llvm.org/show_bug.cgi?id=39088
ClangBuiltLinux/linux#203
ClangBuiltLinux/linux#205
ClangBuiltLinux/linux#207
ClangBuiltLinux/linux#209
ClangBuiltLinux/linux#232


Repository:
  rC Clang

https://reviews.llvm.org/D54188

Files:
  lib/Sema/SemaDeclAttr.cpp
  test/Sema/alias-unused.c


Index: test/Sema/alias-unused.c
===================================================================
--- /dev/null
+++ test/Sema/alias-unused.c
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -Wunneeded-internal-declaration -x c -verify %s
+// expected-no-diagnostics
+int f() { return 42; }
+int g() __attribute__((alias("f")));
+
+static int foo [] = { 42, 0xDEAD };
+extern typeof(foo) bar __attribute__((unused, alias("foo")));
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -1851,7 +1851,16 @@
     }
   }
 
-  // FIXME: check if target symbol exists in current file
+  // Mark target used to prevent unneeded-internal-declaration warnings.
+  if (!S.LangOpts.CPlusPlus) {
+    // FIXME: demangle Str for C++, as the attribute refers to the mangled
+    // linkage name, not the pre-mangled identifier.
+    const DeclarationNameInfo target(&S.Context.Idents.get(Str), AL.getLoc());
+    LookupResult LR(S, target, Sema::LookupOrdinaryName);
+    if (S.LookupQualifiedName(LR, S.getCurLexicalContext()))
+      for (NamedDecl *ND : LR)
+        ND->markUsed(S.Context);
+  }
 
   D->addAttr(::new (S.Context) AliasAttr(AL.getRange(), S.Context, Str,
                                          AL.getAttributeSpellingListIndex()));


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