llvm/lib/Transforms/IPO/ElimAvailExtern.cpp
Rafael Espindola 58019e7bea Disallow aliases to available_externally.
They are as much trouble as aliases to declarations. They are requiring
the code generator to define a symbol with the same value as another
symbol, but the second symbol is undefined.

If representing this is important for some optimization, we could add
support for available_externally aliases. They would be *required* to
point to a declaration (or available_externally definition).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254170 91177308-0d34-0410-b5e6-96231b3b80d8
2015-11-26 19:22:59 +00:00

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2.6 KiB
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//===-- ElimAvailExtern.cpp - DCE unreachable internal functions
//----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This transform is designed to eliminate available external global
// definitions from the program, turning them into declarations.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Module.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
#include "llvm/Pass.h"
using namespace llvm;
#define DEBUG_TYPE "elim-avail-extern"
STATISTIC(NumFunctions, "Number of functions removed");
STATISTIC(NumVariables, "Number of global variables removed");
namespace {
struct EliminateAvailableExternally : public ModulePass {
static char ID; // Pass identification, replacement for typeid
EliminateAvailableExternally() : ModulePass(ID) {
initializeEliminateAvailableExternallyPass(
*PassRegistry::getPassRegistry());
}
// run - Do the EliminateAvailableExternally pass on the specified module,
// optionally updating the specified callgraph to reflect the changes.
//
bool runOnModule(Module &M) override;
};
}
char EliminateAvailableExternally::ID = 0;
INITIALIZE_PASS(EliminateAvailableExternally, "elim-avail-extern",
"Eliminate Available Externally Globals", false, false)
ModulePass *llvm::createEliminateAvailableExternallyPass() {
return new EliminateAvailableExternally();
}
bool EliminateAvailableExternally::runOnModule(Module &M) {
bool Changed = false;
// Drop initializers of available externally global variables.
for (GlobalVariable &GV : M.globals()) {
if (!GV.hasAvailableExternallyLinkage())
continue;
if (GV.hasInitializer()) {
Constant *Init = GV.getInitializer();
GV.setInitializer(nullptr);
if (isSafeToDestroyConstant(Init))
Init->destroyConstant();
}
GV.removeDeadConstantUsers();
GV.setLinkage(GlobalValue::ExternalLinkage);
NumVariables++;
Changed = true;
}
// Drop the bodies of available externally functions.
for (Function &F : M) {
if (!F.hasAvailableExternallyLinkage())
continue;
if (!F.isDeclaration())
// This will set the linkage to external
F.deleteBody();
F.removeDeadConstantUsers();
NumFunctions++;
Changed = true;
}
return Changed;
}