[llvm] r239480 - Add new EliminateAvailableExternally module pass, which is performed in
Teresa Johnson
tejohnson at google.com
Wed Jun 10 10:49:29 PDT 2015
Author: tejohnson
Date: Wed Jun 10 12:49:28 2015
New Revision: 239480
URL: http://llvm.org/viewvc/llvm-project?rev=239480&view=rev
Log:
Add new EliminateAvailableExternally module pass, which is performed in
O2 compiles just before GlobalDCE, unless we are preparing for LTO.
This pass eliminates available externally globals (turning them into
declarations), regardless of whether they are dead/unreferenced, since
we are guaranteed to have a copy available elsewhere at link time.
This enables additional opportunities for GlobalDCE.
If we are preparing for LTO (e.g. a -flto -c compile), the pass is not
included as we want to preserve available externally functions for possible
link time inlining. The FE indicates whether we are doing an -flto compile
via the new PrepareForLTO flag on the PassManagerBuilder.
Added:
llvm/trunk/lib/Transforms/IPO/ElimAvailExtern.cpp
Modified:
llvm/trunk/include/llvm/InitializePasses.h
llvm/trunk/include/llvm/Transforms/IPO.h
llvm/trunk/include/llvm/Transforms/IPO/PassManagerBuilder.h
llvm/trunk/lib/Transforms/IPO/CMakeLists.txt
llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
Modified: llvm/trunk/include/llvm/InitializePasses.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/InitializePasses.h?rev=239480&r1=239479&r2=239480&view=diff
==============================================================================
--- llvm/trunk/include/llvm/InitializePasses.h (original)
+++ llvm/trunk/include/llvm/InitializePasses.h Wed Jun 10 12:49:28 2015
@@ -130,6 +130,7 @@ void initializeSanitizerCoverageModulePa
void initializeDataFlowSanitizerPass(PassRegistry&);
void initializeScalarizerPass(PassRegistry&);
void initializeEarlyCSELegacyPassPass(PassRegistry &);
+void initializeEliminateAvailableExternallyPass(PassRegistry&);
void initializeExpandISelPseudosPass(PassRegistry&);
void initializeFunctionAttrsPass(PassRegistry&);
void initializeGCMachineCodeAnalysisPass(PassRegistry&);
Modified: llvm/trunk/include/llvm/Transforms/IPO.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/IPO.h?rev=239480&r1=239479&r2=239480&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/IPO.h (original)
+++ llvm/trunk/include/llvm/Transforms/IPO.h Wed Jun 10 12:49:28 2015
@@ -71,6 +71,12 @@ ModulePass *createGlobalOptimizerPass();
ModulePass *createGlobalDCEPass();
//===----------------------------------------------------------------------===//
+/// This transform is designed to eliminate available external globals
+/// (functions or global variables)
+///
+ModulePass *createEliminateAvailableExternallyPass();
+
+//===----------------------------------------------------------------------===//
/// createGVExtractionPass - If deleteFn is true, this pass deletes
/// the specified global values. Otherwise, it deletes as much of the module as
/// possible, except for the global values specified.
Modified: llvm/trunk/include/llvm/Transforms/IPO/PassManagerBuilder.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/IPO/PassManagerBuilder.h?rev=239480&r1=239479&r2=239480&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/IPO/PassManagerBuilder.h (original)
+++ llvm/trunk/include/llvm/Transforms/IPO/PassManagerBuilder.h Wed Jun 10 12:49:28 2015
@@ -121,6 +121,7 @@ public:
bool VerifyInput;
bool VerifyOutput;
bool MergeFunctions;
+ bool PrepareForLTO;
private:
/// ExtensionList - This is list of all of the extensions that are registered.
Modified: llvm/trunk/lib/Transforms/IPO/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/CMakeLists.txt?rev=239480&r1=239479&r2=239480&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/CMakeLists.txt (original)
+++ llvm/trunk/lib/Transforms/IPO/CMakeLists.txt Wed Jun 10 12:49:28 2015
@@ -3,6 +3,7 @@ add_llvm_library(LLVMipo
BarrierNoopPass.cpp
ConstantMerge.cpp
DeadArgumentElimination.cpp
+ ElimAvailExtern.cpp
ExtractGV.cpp
FunctionAttrs.cpp
GlobalDCE.cpp
Added: llvm/trunk/lib/Transforms/IPO/ElimAvailExtern.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/ElimAvailExtern.cpp?rev=239480&view=auto
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/ElimAvailExtern.cpp (added)
+++ llvm/trunk/lib/Transforms/IPO/ElimAvailExtern.cpp Wed Jun 10 12:49:28 2015
@@ -0,0 +1,96 @@
+//===-- 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/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Transforms/Utils/CtorUtils.h"
+#include "llvm/Transforms/Utils/GlobalStatus.h"
+#include "llvm/Pass.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "elim-avail-extern"
+
+STATISTIC(NumAliases , "Number of global aliases removed");
+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 (Module::global_iterator I = M.global_begin(), E = M.global_end();
+ I != E; ++I) {
+ if (!I->hasAvailableExternallyLinkage())
+ continue;
+ if (I->hasInitializer()) {
+ Constant *Init = I->getInitializer();
+ I->setInitializer(nullptr);
+ if (isSafeToDestroyConstant(Init))
+ Init->destroyConstant();
+ }
+ I->removeDeadConstantUsers();
+ I->setLinkage(GlobalValue::ExternalLinkage);
+ NumVariables++;
+ }
+
+ // Drop the bodies of available externally functions.
+ for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
+ if (!I->hasAvailableExternallyLinkage())
+ continue;
+ if (!I->isDeclaration())
+ // This will set the linkage to external
+ I->deleteBody();
+ I->removeDeadConstantUsers();
+ NumFunctions++;
+ }
+
+ // Drop targets of available externally aliases.
+ for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E;
+ ++I) {
+ if (!I->hasAvailableExternallyLinkage())
+ continue;
+ I->setAliasee(nullptr);
+ I->removeDeadConstantUsers();
+ I->setLinkage(GlobalValue::ExternalLinkage);
+ NumAliases++;
+ }
+
+ return Changed;
+}
Modified: llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp?rev=239480&r1=239479&r2=239480&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp Wed Jun 10 12:49:28 2015
@@ -105,6 +105,7 @@ PassManagerBuilder::PassManagerBuilder()
VerifyInput = false;
VerifyOutput = false;
MergeFunctions = false;
+ PrepareForLTO = false;
}
PassManagerBuilder::~PassManagerBuilder() {
@@ -401,6 +402,17 @@ void PassManagerBuilder::populateModuleP
// GlobalOpt already deletes dead functions and globals, at -O2 try a
// late pass of GlobalDCE. It is capable of deleting dead cycles.
if (OptLevel > 1) {
+ if (!PrepareForLTO) {
+ // Remove avail extern fns and globals definitions if we aren't
+ // compiling an object file for later LTO. For LTO we want to preserve
+ // these so they are eligible for inlining at link-time. Note if they
+ // are unreferenced they will be removed by GlobalDCE below, so
+ // this only impacts referenced available externally globals.
+ // Eventually they will be suppressed during codegen, but eliminating
+ // here enables more opportunity for GlobalDCE as it may make
+ // globals referenced by available external functions dead.
+ MPM.add(createEliminateAvailableExternallyPass());
+ }
MPM.add(createGlobalDCEPass()); // Remove dead fns and globals.
MPM.add(createConstantMergePass()); // Merge dup global constants
}
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