[GlobalObject] Fix setSection("")

[loladiro]

Summary

In rL291613, the section name was interned in LLVMContext. However,
this broke the ability to remove the section from a GlobalObject,
because it tried to intern empty strings, which is not allowed.
Fix that and add an appropriate regression test.

[rnk]

Lgtm

llvm/trunk/lib/IR/Globals.cpp

 
 void GlobalObject::setSection(StringRef S) {
   // Do nothing if we're clearing the section and it is already empty.
   if (!hasSection() && S.empty())
     return;
 
   // Get or create a stable section name string and put it in the table in the
   // context.
+  if (!S.empty()) {
     S = getContext().pImpl->SectionStrings.insert(S).first->first();
+  }
   getContext().pImpl->GlobalObjectSections[this] = S;
 
   // Update the HasSectionHashEntryBit. Setting the section to the empty string
   // means this global no longer has a section.
   setGlobalObjectFlag(HasSectionHashEntryBit, !S.empty());
 }
 
 bool GlobalValue::isDeclaration() const {

llvm/trunk/unittests/IR/FunctionTest.cpp

 //===- FunctionTest.cpp - Function unit tests -----------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/IR/Function.h"
+#include "llvm/IR/Module.h"
 #include "gtest/gtest.h"
 using namespace llvm;
 
 namespace {
 
 TEST(FunctionTest, hasLazyArguments) {
   LLVMContext C;
 
TEST(FunctionTest, stealArgumentListFrom) {
   // arguments.
   //
   //   steal(empty); drop (real)
   F1->stealArgumentListFrom(*F2);
   EXPECT_TRUE(F1->hasLazyArguments());
   EXPECT_TRUE(F2->hasLazyArguments());
 }
 
+// Test setting and removing section information
+TEST(FunctionTest, setSection) {
+  LLVMContext C;
+  Module M("test", C);
+
+  llvm::Function *F =
+      Function::Create(llvm::FunctionType::get(llvm::Type::getVoidTy(C), false),
+                       llvm::GlobalValue::ExternalLinkage, "F", &M);
+
+  F->setSection(".text.test");
+  EXPECT_TRUE(F->getSection() == ".text.test");
+  EXPECT_TRUE(F->hasSection());
+  F->setSection("");
+  EXPECT_FALSE(F->hasSection());
+  F->setSection(".text.test");
+  F->setSection(".text.test2");
+  EXPECT_TRUE(F->getSection() == ".text.test2");
+  EXPECT_TRUE(F->hasSection());
+}
+
 } // end namespace