forked from OSchip/llvm-project
119 lines
3.9 KiB
C++
119 lines
3.9 KiB
C++
//===------------ BPFIRPeephole.cpp - IR Peephole Transformation ----------===//
|
|
//
|
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
|
|
// See https://llvm.org/LICENSE.txt for license information.
|
|
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// IR level peephole optimization, specifically removing @llvm.stacksave() and
|
|
// @llvm.stackrestore().
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "BPF.h"
|
|
#include "llvm/IR/Instruction.h"
|
|
#include "llvm/IR/Instructions.h"
|
|
#include "llvm/IR/Module.h"
|
|
#include "llvm/IR/PassManager.h"
|
|
#include "llvm/IR/Type.h"
|
|
#include "llvm/IR/User.h"
|
|
#include "llvm/IR/Value.h"
|
|
#include "llvm/Pass.h"
|
|
|
|
#define DEBUG_TYPE "bpf-ir-peephole"
|
|
|
|
using namespace llvm;
|
|
|
|
namespace {
|
|
|
|
static bool BPFIRPeepholeImpl(Function &F) {
|
|
LLVM_DEBUG(dbgs() << "******** BPF IR Peephole ********\n");
|
|
|
|
bool Changed = false;
|
|
Instruction *ToErase = nullptr;
|
|
for (auto &BB : F) {
|
|
for (auto &I : BB) {
|
|
// The following code pattern is handled:
|
|
// %3 = call i8* @llvm.stacksave()
|
|
// store i8* %3, i8** %saved_stack, align 8
|
|
// ...
|
|
// %4 = load i8*, i8** %saved_stack, align 8
|
|
// call void @llvm.stackrestore(i8* %4)
|
|
// ...
|
|
// The goal is to remove the above four instructions,
|
|
// so we won't have instructions with r11 (stack pointer)
|
|
// if eventually there is no variable length stack allocation.
|
|
// InstrCombine also tries to remove the above instructions,
|
|
// if it is proven safe (constant alloca etc.), but depending
|
|
// on code pattern, it may still miss some.
|
|
//
|
|
// With unconditionally removing these instructions, if alloca is
|
|
// constant, we are okay then. Otherwise, SelectionDag will complain
|
|
// since BPF does not support dynamic allocation yet.
|
|
if (ToErase) {
|
|
ToErase->eraseFromParent();
|
|
ToErase = nullptr;
|
|
}
|
|
|
|
if (auto *Call = dyn_cast<CallInst>(&I)) {
|
|
if (auto *GV = dyn_cast<GlobalValue>(Call->getCalledOperand())) {
|
|
if (!GV->getName().equals("llvm.stacksave"))
|
|
continue;
|
|
if (!Call->hasOneUser())
|
|
continue;
|
|
auto *Inst = cast<Instruction>(*Call->user_begin());
|
|
LLVM_DEBUG(dbgs() << "Remove:"; I.dump());
|
|
LLVM_DEBUG(dbgs() << "Remove:"; Inst->dump(); dbgs() << '\n');
|
|
Changed = true;
|
|
Inst->eraseFromParent();
|
|
ToErase = &I;
|
|
}
|
|
continue;
|
|
}
|
|
|
|
if (auto *LD = dyn_cast<LoadInst>(&I)) {
|
|
if (!LD->hasOneUser())
|
|
continue;
|
|
auto *Call = dyn_cast<CallInst>(*LD->user_begin());
|
|
if (!Call)
|
|
continue;
|
|
auto *GV = dyn_cast<GlobalValue>(Call->getCalledOperand());
|
|
if (!GV)
|
|
continue;
|
|
if (!GV->getName().equals("llvm.stackrestore"))
|
|
continue;
|
|
LLVM_DEBUG(dbgs() << "Remove:"; I.dump());
|
|
LLVM_DEBUG(dbgs() << "Remove:"; Call->dump(); dbgs() << '\n');
|
|
Changed = true;
|
|
Call->eraseFromParent();
|
|
ToErase = &I;
|
|
}
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
class BPFIRPeephole final : public FunctionPass {
|
|
bool runOnFunction(Function &F) override;
|
|
|
|
public:
|
|
static char ID;
|
|
BPFIRPeephole() : FunctionPass(ID) {}
|
|
};
|
|
} // End anonymous namespace
|
|
|
|
char BPFIRPeephole::ID = 0;
|
|
INITIALIZE_PASS(BPFIRPeephole, DEBUG_TYPE, "BPF IR Peephole", false, false)
|
|
|
|
FunctionPass *llvm::createBPFIRPeephole() { return new BPFIRPeephole(); }
|
|
|
|
bool BPFIRPeephole::runOnFunction(Function &F) { return BPFIRPeepholeImpl(F); }
|
|
|
|
PreservedAnalyses BPFIRPeepholePass::run(Function &F,
|
|
FunctionAnalysisManager &AM) {
|
|
return BPFIRPeepholeImpl(F) ? PreservedAnalyses::none()
|
|
: PreservedAnalyses::all();
|
|
}
|