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d215bba299
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). llvm-svn: 254170
85 lines
2.6 KiB
C++
85 lines
2.6 KiB
C++
//===-- ElimAvailExtern.cpp - DCE unreachable internal functions
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//----------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This transform is designed to eliminate available external global
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// definitions from the program, turning them into declarations.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/IPO.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Transforms/Utils/GlobalStatus.h"
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#include "llvm/Pass.h"
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using namespace llvm;
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#define DEBUG_TYPE "elim-avail-extern"
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STATISTIC(NumFunctions, "Number of functions removed");
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STATISTIC(NumVariables, "Number of global variables removed");
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namespace {
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struct EliminateAvailableExternally : public ModulePass {
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static char ID; // Pass identification, replacement for typeid
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EliminateAvailableExternally() : ModulePass(ID) {
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initializeEliminateAvailableExternallyPass(
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*PassRegistry::getPassRegistry());
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}
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// run - Do the EliminateAvailableExternally pass on the specified module,
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// optionally updating the specified callgraph to reflect the changes.
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//
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bool runOnModule(Module &M) override;
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};
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}
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char EliminateAvailableExternally::ID = 0;
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INITIALIZE_PASS(EliminateAvailableExternally, "elim-avail-extern",
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"Eliminate Available Externally Globals", false, false)
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ModulePass *llvm::createEliminateAvailableExternallyPass() {
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return new EliminateAvailableExternally();
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}
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bool EliminateAvailableExternally::runOnModule(Module &M) {
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bool Changed = false;
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// Drop initializers of available externally global variables.
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for (GlobalVariable &GV : M.globals()) {
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if (!GV.hasAvailableExternallyLinkage())
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continue;
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if (GV.hasInitializer()) {
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Constant *Init = GV.getInitializer();
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GV.setInitializer(nullptr);
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if (isSafeToDestroyConstant(Init))
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Init->destroyConstant();
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}
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GV.removeDeadConstantUsers();
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GV.setLinkage(GlobalValue::ExternalLinkage);
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NumVariables++;
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Changed = true;
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}
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// Drop the bodies of available externally functions.
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for (Function &F : M) {
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if (!F.hasAvailableExternallyLinkage())
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continue;
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if (!F.isDeclaration())
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// This will set the linkage to external
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F.deleteBody();
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F.removeDeadConstantUsers();
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NumFunctions++;
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Changed = true;
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}
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return Changed;
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}
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