forked from OSchip/llvm-project
94 lines
3.7 KiB
C++
94 lines
3.7 KiB
C++
//===-- ImplicitControlFlowTracking.cpp -------------------------*- C++ -*-===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
// This class allows to keep track on instructions with implicit control flow.
|
|
// These are instructions that may not pass execution to their successors. For
|
|
// example, throwing calls and guards do not always do this. If we need to know
|
|
// for sure that some instruction is guaranteed to execute if the given block
|
|
// is reached, then we need to make sure that there is no implicit control flow
|
|
// instruction (ICFI) preceeding it. For example, this check is required if we
|
|
// perform PRE moving non-speculable instruction to other place.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Analysis/ValueTracking.h"
|
|
#include "llvm/Transforms/Utils/ImplicitControlFlowTracking.h"
|
|
|
|
using namespace llvm;
|
|
|
|
const Instruction *
|
|
ImplicitControlFlowTracking::getFirstICFI(const BasicBlock *BB) {
|
|
if (!KnownBlocks.count(BB))
|
|
fill(BB);
|
|
auto *FirstICF = FirstImplicitControlFlowInsts.lookup(BB);
|
|
assert((!FirstICF || FirstICF->getParent() == BB) && "Inconsistent cache!");
|
|
return FirstICF;
|
|
}
|
|
|
|
bool ImplicitControlFlowTracking::hasICF(const BasicBlock *BB) {
|
|
return getFirstICFI(BB) != nullptr;
|
|
}
|
|
|
|
bool ImplicitControlFlowTracking::isDominatedByICFIFromSameBlock(
|
|
const Instruction *Insn) {
|
|
const Instruction *MaybeFirstICF = getFirstICFI(Insn->getParent());
|
|
return MaybeFirstICF && OI.dominates(MaybeFirstICF, Insn);
|
|
}
|
|
|
|
void ImplicitControlFlowTracking::fill(const BasicBlock *BB) {
|
|
auto MayNotTransferExecutionToSuccessor = [&](const Instruction *I) {
|
|
// 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.
|
|
//
|
|
// TODO: Currently, isGuaranteedToTransferExecutionToSuccessor returns false
|
|
// for volatile stores and loads because they can trap. The discussion on
|
|
// whether or not it is correct is still ongoing. We might want to get rid
|
|
// of this logic in the future. Anyways, trapping instructions shouldn't
|
|
// introduce implicit control flow, so we explicitly allow them here. This
|
|
// must be removed once isGuaranteedToTransferExecutionToSuccessor is fixed.
|
|
if (isGuaranteedToTransferExecutionToSuccessor(I))
|
|
return false;
|
|
if (isa<LoadInst>(I)) {
|
|
assert(cast<LoadInst>(I)->isVolatile() &&
|
|
"Non-volatile load should transfer execution to successor!");
|
|
return false;
|
|
}
|
|
if (isa<StoreInst>(I)) {
|
|
assert(cast<StoreInst>(I)->isVolatile() &&
|
|
"Non-volatile store should transfer execution to successor!");
|
|
return false;
|
|
}
|
|
return true;
|
|
};
|
|
FirstImplicitControlFlowInsts.erase(BB);
|
|
|
|
for (auto &I : *BB)
|
|
if (MayNotTransferExecutionToSuccessor(&I)) {
|
|
FirstImplicitControlFlowInsts[BB] = &I;
|
|
break;
|
|
}
|
|
|
|
// Mark this block as having a known result.
|
|
KnownBlocks.insert(BB);
|
|
}
|
|
|
|
void ImplicitControlFlowTracking::invalidateBlock(const BasicBlock *BB) {
|
|
OI.invalidateBlock(BB);
|
|
FirstImplicitControlFlowInsts.erase(BB);
|
|
KnownBlocks.erase(BB);
|
|
}
|
|
|
|
void ImplicitControlFlowTracking::clear() {
|
|
for (auto It : FirstImplicitControlFlowInsts)
|
|
OI.invalidateBlock(It.first);
|
|
FirstImplicitControlFlowInsts.clear();
|
|
KnownBlocks.clear();
|
|
}
|