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//===- SplitModule.cpp - Split a module into partitions -------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the function llvm::SplitModule, which splits a module
// into multiple linkable partitions. It can be used to implement parallel code
// generation for link-time optimization.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/SplitModule.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalObject.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/MD5.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Cloning.h"
using namespace llvm;
static void externalize(GlobalValue *GV) {
if (GV->hasLocalLinkage()) {
GV->setLinkage(GlobalValue::ExternalLinkage);
GV->setVisibility(GlobalValue::HiddenVisibility);
}
// Unnamed entities must be named consistently between modules. setName will
// give a distinct name to each such entity.
if (!GV->hasName())
GV->setName("__llvmsplit_unnamed");
}
// Returns whether GV should be in partition (0-based) I of N.
static bool isInPartition(const GlobalValue *GV, unsigned I, unsigned N) {
if (auto GA = dyn_cast<GlobalAlias>(GV))
if (const GlobalObject *Base = GA->getBaseObject())
GV = Base;
StringRef Name;
if (const Comdat *C = GV->getComdat())
Name = C->getName();
else
Name = GV->getName();
// Partition by MD5 hash. We only need a few bits for evenness as the number
// of partitions will generally be in the 1-2 figure range; the low 16 bits
// are enough.
MD5 H;
MD5::MD5Result R;
H.update(Name);
H.final(R);
return (R[0] | (R[1] << 8)) % N == I;
}
void llvm::SplitModule(
std::unique_ptr<Module> M, unsigned N,
std::function<void(std::unique_ptr<Module> MPart)> ModuleCallback) {
for (Function &F : *M)
externalize(&F);
for (GlobalVariable &GV : M->globals())
externalize(&GV);
for (GlobalAlias &GA : M->aliases())
externalize(&GA);
// FIXME: We should be able to reuse M as the last partition instead of
// cloning it.
for (unsigned I = 0; I != N; ++I) {
ValueToValueMapTy VMap;
std::unique_ptr<Module> MPart(
CloneModule(M.get(), VMap, [=](const GlobalValue *GV) {
return isInPartition(GV, I, N);
}));
if (I != 0)
MPart->setModuleInlineAsm("");
ModuleCallback(std::move(MPart));
}
}
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