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127 lines
4.7 KiB
C++
127 lines
4.7 KiB
C++
//===-- GuardUtils.cpp - Utils for work with guards -------------*- C++ -*-===//
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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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// Utils that are used to perform transformations related to guards and their
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// conditions.
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/GuardUtils.h"
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#include "llvm/Analysis/GuardUtils.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/MDBuilder.h"
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#include "llvm/IR/PatternMatch.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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using namespace llvm;
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using namespace llvm::PatternMatch;
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static cl::opt<uint32_t> PredicatePassBranchWeight(
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"guards-predicate-pass-branch-weight", cl::Hidden, cl::init(1 << 20),
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cl::desc("The probability of a guard failing is assumed to be the "
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"reciprocal of this value (default = 1 << 20)"));
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void llvm::makeGuardControlFlowExplicit(Function *DeoptIntrinsic,
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CallInst *Guard, bool UseWC) {
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OperandBundleDef DeoptOB(*Guard->getOperandBundle(LLVMContext::OB_deopt));
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SmallVector<Value *, 4> Args(drop_begin(Guard->args()));
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auto *CheckBB = Guard->getParent();
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auto *DeoptBlockTerm =
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SplitBlockAndInsertIfThen(Guard->getArgOperand(0), Guard, true);
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auto *CheckBI = cast<BranchInst>(CheckBB->getTerminator());
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// SplitBlockAndInsertIfThen inserts control flow that branches to
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// DeoptBlockTerm if the condition is true. We want the opposite.
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CheckBI->swapSuccessors();
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CheckBI->getSuccessor(0)->setName("guarded");
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CheckBI->getSuccessor(1)->setName("deopt");
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if (auto *MD = Guard->getMetadata(LLVMContext::MD_make_implicit))
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CheckBI->setMetadata(LLVMContext::MD_make_implicit, MD);
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MDBuilder MDB(Guard->getContext());
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CheckBI->setMetadata(LLVMContext::MD_prof,
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MDB.createBranchWeights(PredicatePassBranchWeight, 1));
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IRBuilder<> B(DeoptBlockTerm);
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auto *DeoptCall = B.CreateCall(DeoptIntrinsic, Args, {DeoptOB}, "");
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if (DeoptIntrinsic->getReturnType()->isVoidTy()) {
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B.CreateRetVoid();
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} else {
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DeoptCall->setName("deoptcall");
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B.CreateRet(DeoptCall);
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}
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DeoptCall->setCallingConv(Guard->getCallingConv());
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DeoptBlockTerm->eraseFromParent();
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if (UseWC) {
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// We want the guard to be expressed as explicit control flow, but still be
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// widenable. For that, we add Widenable Condition intrinsic call to the
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// guard's condition.
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IRBuilder<> B(CheckBI);
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auto *WC = B.CreateIntrinsic(Intrinsic::experimental_widenable_condition,
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{}, {}, nullptr, "widenable_cond");
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CheckBI->setCondition(B.CreateAnd(CheckBI->getCondition(), WC,
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"exiplicit_guard_cond"));
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assert(isWidenableBranch(CheckBI) && "sanity check");
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}
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}
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void llvm::widenWidenableBranch(BranchInst *WidenableBR, Value *NewCond) {
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assert(isWidenableBranch(WidenableBR) && "precondition");
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// The tempting trivially option is to produce something like this:
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// br (and oldcond, newcond) where oldcond is assumed to contain a widenable
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// condition, but that doesn't match the pattern parseWidenableBranch expects
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// so we have to be more sophisticated.
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Use *C, *WC;
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BasicBlock *IfTrueBB, *IfFalseBB;
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parseWidenableBranch(WidenableBR, C, WC, IfTrueBB, IfFalseBB);
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if (!C) {
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// br (wc()), ... form
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IRBuilder<> B(WidenableBR);
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WidenableBR->setCondition(B.CreateAnd(NewCond, WC->get()));
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} else {
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// br (wc & C), ... form
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IRBuilder<> B(WidenableBR);
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C->set(B.CreateAnd(NewCond, C->get()));
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Instruction *WCAnd = cast<Instruction>(WidenableBR->getCondition());
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// Condition is only guaranteed to dominate branch
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WCAnd->moveBefore(WidenableBR);
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}
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assert(isWidenableBranch(WidenableBR) && "preserve widenabiliy");
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}
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void llvm::setWidenableBranchCond(BranchInst *WidenableBR, Value *NewCond) {
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assert(isWidenableBranch(WidenableBR) && "precondition");
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Use *C, *WC;
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BasicBlock *IfTrueBB, *IfFalseBB;
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parseWidenableBranch(WidenableBR, C, WC, IfTrueBB, IfFalseBB);
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if (!C) {
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// br (wc()), ... form
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IRBuilder<> B(WidenableBR);
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WidenableBR->setCondition(B.CreateAnd(NewCond, WC->get()));
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} else {
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// br (wc & C), ... form
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Instruction *WCAnd = cast<Instruction>(WidenableBR->getCondition());
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// Condition is only guaranteed to dominate branch
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WCAnd->moveBefore(WidenableBR);
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C->set(NewCond);
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}
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assert(isWidenableBranch(WidenableBR) && "preserve widenabiliy");
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}
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