From 0fad0d7724339d9397ad55ec6c9580a9236dad17 Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Tue, 22 Oct 2013 13:51:06 +0000
Subject: This patch causes clang to reject alias attributes that point to
 undefined names. For example, with this patch we now reject

void f1(void) __attribute__((alias("g1")));

This patch is implemented in CodeGen. It is quiet a bit simpler and more
compatible with gcc than implementing it in Sema. The downside is that the
errors only fire during -emit-llvm.

llvm-svn: 193161
---
 clang/lib/CodeGen/CodeGenModule.cpp | 39 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

(limited to 'clang/lib/CodeGen/CodeGenModule.cpp')

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 96ae437..2939b4a 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -37,6 +37,7 @@
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/Version.h"
 #include "clang/Frontend/CodeGenOptions.h"
+#include "clang/Sema/SemaDiagnostic.h"
 #include "llvm/ADT/APSInt.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/IR/CallingConv.h"
@@ -933,6 +934,12 @@ void CodeGenModule::EmitDeferred() {
     GlobalDecl D = DeferredDeclsToEmit.back();
     DeferredDeclsToEmit.pop_back();
 
+    const ValueDecl *Global = cast<ValueDecl>(D.getDecl());
+    if (Global->hasAttr<AliasAttr>()) {
+      EmitAliasDefinition(D);
+      continue;
+    }
+
     // Check to see if we've already emitted this.  This is necessary
     // for a couple of reasons: first, decls can end up in the
     // deferred-decls queue multiple times, and second, decls can end
@@ -1098,7 +1105,7 @@ void CodeGenModule::EmitGlobal(GlobalDecl GD) {
   // If this is an alias definition (which otherwise looks like a declaration)
   // emit it now.
   if (Global->hasAttr<AliasAttr>())
-    return EmitAliasDefinition(GD);
+    return scheduleAliasDefinitionEmission(GD);
 
   // If this is CUDA, be selective about which declarations we emit.
   if (LangOpts.CUDA) {
@@ -2075,6 +2082,24 @@ void CodeGenModule::EmitGlobalFunctionDefinition(GlobalDecl GD) {
     AddGlobalAnnotations(D, Fn);
 }
 
+void CodeGenModule::scheduleAliasDefinitionEmission(GlobalDecl GD) {
+  const ValueDecl *D = cast<ValueDecl>(GD.getDecl());
+  const AliasAttr *AA = D->getAttr<AliasAttr>();
+  assert(AA && "Not an alias?");
+
+  // Schedule it.
+  DeferredDeclsToEmit.push_back(GD);
+
+  llvm::Type *DeclTy = getTypes().ConvertTypeForMem(D->getType());
+
+  // Cause the aliasee emission to be scheduled.
+  if (isa<llvm::FunctionType>(DeclTy))
+    GetOrCreateLLVMFunction(AA->getAliasee(), DeclTy, GD, /*ForVTable=*/false);
+  else
+    GetOrCreateLLVMGlobal(AA->getAliasee(),
+                          llvm::PointerType::getUnqual(DeclTy), 0);
+}
+
 void CodeGenModule::EmitAliasDefinition(GlobalDecl GD) {
   const ValueDecl *D = cast<ValueDecl>(GD.getDecl());
   const AliasAttr *AA = D->getAttr<AliasAttr>();
@@ -2100,6 +2125,18 @@ void CodeGenModule::EmitAliasDefinition(GlobalDecl GD) {
     Aliasee = GetOrCreateLLVMGlobal(AA->getAliasee(),
                                     llvm::PointerType::getUnqual(DeclTy), 0);
 
+  llvm::GlobalValue *GV = dyn_cast<llvm::GlobalValue>(Aliasee);
+  if (!GV) {
+    llvm::ConstantExpr *CE = cast<llvm::ConstantExpr>(Aliasee);
+    assert(CE->getOpcode() == llvm::Instruction::BitCast ||
+           CE->getOpcode() == llvm::Instruction::GetElementPtr);
+    GV = cast<llvm::GlobalValue>(CE->getOperand(0));
+  }
+  if (GV->isDeclaration()) {
+    getDiags().Report(AA->getLocation(), diag::err_alias_to_undefined);
+    return;
+  }
+
   // Create the new alias itself, but don't set a name yet.
   llvm::GlobalValue *GA =
     new llvm::GlobalAlias(Aliasee->getType(),
-- 
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