r246882 - Don't crash on a self-alias declaration

[Hal Finkel via cfe-commits]

Author: hfinkel
Date: Fri Sep  4 16:49:21 2015
New Revision: 246882

URL: http://llvm.org/viewvc/llvm-project?rev=246882&view=rev
Log:
Don't crash on a self-alias declaration

We were crashing in CodeGen given input like this:

  int self_alias(void) __attribute__((weak, alias("self_alias")));

such a self-alias is invalid, but instead of diagnosing the situation, we'd
proceed to produce IR for both the function declaration and the alias. Because
we already had a function named 'self_alias', the alias could not be named the
same thing, and so LLVM would pick a different name ('self_alias1' for example)
for that value. When we later called CodeGenModule::checkAliases, we'd look up
the IR value corresponding to the alias name, find the function declaration
instead, and then assert in a cast to llvm::GlobalAlias. The easiest way to prevent
this is simply to avoid creating the wrongly-named alias value in the first
place and issue the diagnostic there (instead of in checkAliases). We detect a
related cycle case in CodeGenModule::EmitAliasDefinition already, so this just
adds a second such check.

Even though the other test cases for this 'alias definition is part of a cycle'
diagnostic are in test/Sema/attr-alias-elf.c, I've added a separate regression
test for this case. This is because I can't add this check to
test/Sema/attr-alias-elf.c without disturbing the other test cases in that
file. In order to avoid construction of the bad IR values, this diagnostic
is emitted from within CodeGenModule::EmitAliasDefinition (and the relevant
declaration is not added to the Aliases vector). The other cycle checks are
done within the CodeGenModule::checkAliases function based on the Aliases
vector, called from CodeGenModule::Release.  However, if there have been errors
earlier, HandleTranslationUnit does not call Release, and so checkAliases is
never called, and so none of the other diagnostics would be produced.

Fixes PR23509.

Added:
    cfe/trunk/test/Sema/attr-self-alias.c
Modified:
    cfe/trunk/lib/CodeGen/CodeGenModule.cpp

Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=246882&r1=246881&r2=246882&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Fri Sep  4 16:49:21 2015
@@ -2613,6 +2613,11 @@ void CodeGenModule::EmitAliasDefinition(
 
   StringRef MangledName = getMangledName(GD);
 
+  if (AA->getAliasee() == MangledName) {
+    Diags.Report(AA->getLocation(), diag::err_cyclic_alias);
+    return;
+  }
+
   // If there is a definition in the module, then it wins over the alias.
   // This is dubious, but allow it to be safe.  Just ignore the alias.
   llvm::GlobalValue *Entry = GetGlobalValue(MangledName);

Added: cfe/trunk/test/Sema/attr-self-alias.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/attr-self-alias.c?rev=246882&view=auto
==============================================================================
--- cfe/trunk/test/Sema/attr-self-alias.c (added)
+++ cfe/trunk/test/Sema/attr-self-alias.c Fri Sep  4 16:49:21 2015
@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -triple x86_64-pc-linux  -fsyntax-only -verify -emit-llvm-only %s
+
+int self_alias(void) __attribute__((weak, alias("self_alias"))); // expected-error {{alias definition is part of a cycle}}
+