05da2fe521
This file lists every pass in LLVM, and is included by Pass.h, which is very popular. Every time we add, remove, or rename a pass in LLVM, it caused lots of recompilation. I found this fact by looking at this table, which is sorted by the number of times a file was changed over the last 100,000 git commits multiplied by the number of object files that depend on it in the current checkout: recompiles touches affected_files header 342380 95 3604 llvm/include/llvm/ADT/STLExtras.h 314730 234 1345 llvm/include/llvm/InitializePasses.h 307036 118 2602 llvm/include/llvm/ADT/APInt.h 213049 59 3611 llvm/include/llvm/Support/MathExtras.h 170422 47 3626 llvm/include/llvm/Support/Compiler.h 162225 45 3605 llvm/include/llvm/ADT/Optional.h 158319 63 2513 llvm/include/llvm/ADT/Triple.h 140322 39 3598 llvm/include/llvm/ADT/StringRef.h 137647 59 2333 llvm/include/llvm/Support/Error.h 131619 73 1803 llvm/include/llvm/Support/FileSystem.h Before this change, touching InitializePasses.h would cause 1345 files to recompile. After this change, touching it only causes 550 compiles in an incremental rebuild. Reviewers: bkramer, asbirlea, bollu, jdoerfert Differential Revision: https://reviews.llvm.org/D70211
130 lines
4.3 KiB
C++
130 lines
4.3 KiB
C++
//===- Reg2Mem.cpp - Convert registers to allocas -------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file demotes all registers to memory references. It is intended to be
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// the inverse of PromoteMemoryToRegister. By converting to loads, the only
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// values live across basic blocks are allocas and loads before phi nodes.
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// It is intended that this should make CFG hacking much easier.
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// To make later hacking easier, the entry block is split into two, such that
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// all introduced allocas and nothing else are in the entry block.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/Statistic.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Module.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Utils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include <list>
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using namespace llvm;
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#define DEBUG_TYPE "reg2mem"
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STATISTIC(NumRegsDemoted, "Number of registers demoted");
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STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted");
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namespace {
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struct RegToMem : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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RegToMem() : FunctionPass(ID) {
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initializeRegToMemPass(*PassRegistry::getPassRegistry());
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequiredID(BreakCriticalEdgesID);
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AU.addPreservedID(BreakCriticalEdgesID);
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}
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bool valueEscapes(const Instruction *Inst) const {
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const BasicBlock *BB = Inst->getParent();
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for (const User *U : Inst->users()) {
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const Instruction *UI = cast<Instruction>(U);
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if (UI->getParent() != BB || isa<PHINode>(UI))
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return true;
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}
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return false;
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}
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bool runOnFunction(Function &F) override;
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};
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}
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char RegToMem::ID = 0;
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INITIALIZE_PASS_BEGIN(RegToMem, "reg2mem", "Demote all values to stack slots",
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false, false)
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INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
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INITIALIZE_PASS_END(RegToMem, "reg2mem", "Demote all values to stack slots",
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false, false)
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bool RegToMem::runOnFunction(Function &F) {
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if (F.isDeclaration() || skipFunction(F))
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return false;
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// Insert all new allocas into entry block.
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BasicBlock *BBEntry = &F.getEntryBlock();
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assert(pred_empty(BBEntry) &&
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"Entry block to function must not have predecessors!");
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// Find first non-alloca instruction and create insertion point. This is
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// safe if block is well-formed: it always have terminator, otherwise
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// we'll get and assertion.
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BasicBlock::iterator I = BBEntry->begin();
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while (isa<AllocaInst>(I)) ++I;
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CastInst *AllocaInsertionPoint = new BitCastInst(
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Constant::getNullValue(Type::getInt32Ty(F.getContext())),
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Type::getInt32Ty(F.getContext()), "reg2mem alloca point", &*I);
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// Find the escaped instructions. But don't create stack slots for
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// allocas in entry block.
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std::list<Instruction*> WorkList;
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for (BasicBlock &ibb : F)
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for (BasicBlock::iterator iib = ibb.begin(), iie = ibb.end(); iib != iie;
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++iib) {
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if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) &&
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valueEscapes(&*iib)) {
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WorkList.push_front(&*iib);
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}
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}
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// Demote escaped instructions
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NumRegsDemoted += WorkList.size();
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for (Instruction *ilb : WorkList)
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DemoteRegToStack(*ilb, false, AllocaInsertionPoint);
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WorkList.clear();
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// Find all phi's
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for (BasicBlock &ibb : F)
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for (BasicBlock::iterator iib = ibb.begin(), iie = ibb.end(); iib != iie;
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++iib)
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if (isa<PHINode>(iib))
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WorkList.push_front(&*iib);
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// Demote phi nodes
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NumPhisDemoted += WorkList.size();
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for (Instruction *ilb : WorkList)
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DemotePHIToStack(cast<PHINode>(ilb), AllocaInsertionPoint);
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return true;
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}
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// createDemoteRegisterToMemory - Provide an entry point to create this pass.
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char &llvm::DemoteRegisterToMemoryID = RegToMem::ID;
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FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
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return new RegToMem();
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}
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