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//===-- InstructionPrecedenceTracking.cpp -----------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
// Implements a class that is able to define some instructions as "special"
// (e.g. as having implicit control flow, or writing memory, or having another
// interesting property) and then efficiently answers queries of the types:
// 1. Are there any special instructions in the block of interest?
// 2. Return first of the special instructions in the given block;
// 3. Check if the given instruction is preceeded by the first special
// instruction in the same block.
// The class provides caching that allows to answer these queries quickly. The
// user must make sure that the cached data is invalidated properly whenever
// a content of some tracked block is changed.
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/InstructionPrecedenceTracking.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/CommandLine.h"
using namespace llvm;
#define DEBUG_TYPE "ipt"
STATISTIC(NumInstScanned, "Number of insts scanned while updating ibt");
#ifndef NDEBUG
static cl::opt<bool> ExpensiveAsserts(
"ipt-expensive-asserts",
cl::desc("Perform expensive assert validation on every query to Instruction"
" Precedence Tracking"),
cl::init(false), cl::Hidden);
#endif
const Instruction *InstructionPrecedenceTracking::getFirstSpecialInstruction(
const BasicBlock *BB) {
#ifndef NDEBUG
// If there is a bug connected to invalid cache, turn on ExpensiveAsserts to
// catch this situation as early as possible.
if (ExpensiveAsserts)
validateAll();
else
validate(BB);
#endif
if (FirstSpecialInsts.find(BB) == FirstSpecialInsts.end()) {
fill(BB);
assert(FirstSpecialInsts.find(BB) != FirstSpecialInsts.end() && "Must be!");
}
return FirstSpecialInsts[BB];
}
bool InstructionPrecedenceTracking::hasSpecialInstructions(
const BasicBlock *BB) {
return getFirstSpecialInstruction(BB) != nullptr;
}
bool InstructionPrecedenceTracking::isPreceededBySpecialInstruction(
const Instruction *Insn) {
const Instruction *MaybeFirstSpecial =
getFirstSpecialInstruction(Insn->getParent());
return MaybeFirstSpecial && MaybeFirstSpecial->comesBefore(Insn);
}
void InstructionPrecedenceTracking::fill(const BasicBlock *BB) {
FirstSpecialInsts.erase(BB);
for (const auto &I : *BB) {
NumInstScanned++;
if (isSpecialInstruction(&I)) {
FirstSpecialInsts[BB] = &I;
return;
}
}
// Mark this block as having no special instructions.
FirstSpecialInsts[BB] = nullptr;
}
#ifndef NDEBUG
void InstructionPrecedenceTracking::validate(const BasicBlock *BB) const {
auto It = FirstSpecialInsts.find(BB);
// Bail if we don't have anything cached for this block.
if (It == FirstSpecialInsts.end())
return;
for (const Instruction &Insn : *BB)
if (isSpecialInstruction(&Insn)) {
assert(It->second == &Insn &&
"Cached first special instruction is wrong!");
return;
}
assert(It->second == nullptr &&
"Block is marked as having special instructions but in fact it has "
"none!");
}
void InstructionPrecedenceTracking::validateAll() const {
// Check that for every known block the cached value is correct.
for (const auto &It : FirstSpecialInsts)
validate(It.first);
}
#endif
void InstructionPrecedenceTracking::insertInstructionTo(const Instruction *Inst,
const BasicBlock *BB) {
if (isSpecialInstruction(Inst))
FirstSpecialInsts.erase(BB);
}
void InstructionPrecedenceTracking::removeInstruction(const Instruction *Inst) {
auto *BB = Inst->getParent();
assert(BB && "must be called before instruction is actually removed");
if (FirstSpecialInsts.count(BB) && FirstSpecialInsts[BB] == Inst)
FirstSpecialInsts.erase(BB);
}
void InstructionPrecedenceTracking::removeUsersOf(const Instruction *Inst) {
for (const auto *U : Inst->users()) {
if (const auto *UI = dyn_cast<Instruction>(U))
removeInstruction(UI);
}
}
void InstructionPrecedenceTracking::clear() {
FirstSpecialInsts.clear();
#ifndef NDEBUG
// The map should be valid after clearing (at least empty).
validateAll();
#endif
}
bool ImplicitControlFlowTracking::isSpecialInstruction(
const Instruction *Insn) const {
// If a block's instruction doesn't always pass the control to its successor
// instruction, mark the block as having implicit control flow. We use them
// to avoid wrong assumptions of sort "if A is executed and B post-dominates
// A, then B is also executed". This is not true is there is an implicit
// control flow instruction (e.g. a guard) between them.
return !isGuaranteedToTransferExecutionToSuccessor(Insn);
}
bool MemoryWriteTracking::isSpecialInstruction(
const Instruction *Insn) const {
using namespace PatternMatch;
if (match(Insn, m_Intrinsic<Intrinsic::experimental_widenable_condition>()))
return false;
return Insn->mayWriteToMemory();
}
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