1//===-- GuardUtils.cpp - Utils for work with guards -------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8// Utils that are used to perform transformations related to guards and their
9// conditions.
10//===----------------------------------------------------------------------===//
11
12#include "llvm/Transforms/Utils/GuardUtils.h"
13#include "llvm/Analysis/GuardUtils.h"
14#include "llvm/IR/Function.h"
15#include "llvm/IR/IRBuilder.h"
16#include "llvm/IR/Instructions.h"
17#include "llvm/IR/MDBuilder.h"
18#include "llvm/IR/PatternMatch.h"
19#include "llvm/Support/CommandLine.h"
20#include "llvm/Transforms/Utils/BasicBlockUtils.h"
21
22using namespace llvm;
23using namespace llvm::PatternMatch;
24
25static cl::opt<uint32_t> PredicatePassBranchWeight(
26    "guards-predicate-pass-branch-weight", cl::Hidden, cl::init(1 << 20),
27    cl::desc("The probability of a guard failing is assumed to be the "
28             "reciprocal of this value (default = 1 << 20)"));
29
30void llvm::makeGuardControlFlowExplicit(Function *DeoptIntrinsic,
31                                        CallInst *Guard, bool UseWC) {
32  OperandBundleDef DeoptOB(*Guard->getOperandBundle(LLVMContext::OB_deopt));
33  SmallVector<Value *, 4> Args(std::next(Guard->arg_begin()), Guard->arg_end());
34
35  auto *CheckBB = Guard->getParent();
36  auto *DeoptBlockTerm =
37      SplitBlockAndInsertIfThen(Guard->getArgOperand(0), Guard, true);
38
39  auto *CheckBI = cast<BranchInst>(CheckBB->getTerminator());
40
41  // SplitBlockAndInsertIfThen inserts control flow that branches to
42  // DeoptBlockTerm if the condition is true.  We want the opposite.
43  CheckBI->swapSuccessors();
44
45  CheckBI->getSuccessor(0)->setName("guarded");
46  CheckBI->getSuccessor(1)->setName("deopt");
47
48  if (auto *MD = Guard->getMetadata(LLVMContext::MD_make_implicit))
49    CheckBI->setMetadata(LLVMContext::MD_make_implicit, MD);
50
51  MDBuilder MDB(Guard->getContext());
52  CheckBI->setMetadata(LLVMContext::MD_prof,
53                       MDB.createBranchWeights(PredicatePassBranchWeight, 1));
54
55  IRBuilder<> B(DeoptBlockTerm);
56  auto *DeoptCall = B.CreateCall(DeoptIntrinsic, Args, {DeoptOB}, "");
57
58  if (DeoptIntrinsic->getReturnType()->isVoidTy()) {
59    B.CreateRetVoid();
60  } else {
61    DeoptCall->setName("deoptcall");
62    B.CreateRet(DeoptCall);
63  }
64
65  DeoptCall->setCallingConv(Guard->getCallingConv());
66  DeoptBlockTerm->eraseFromParent();
67
68  if (UseWC) {
69    // We want the guard to be expressed as explicit control flow, but still be
70    // widenable. For that, we add Widenable Condition intrinsic call to the
71    // guard's condition.
72    IRBuilder<> B(CheckBI);
73    auto *WC = B.CreateIntrinsic(Intrinsic::experimental_widenable_condition,
74                                 {}, {}, nullptr, "widenable_cond");
75    CheckBI->setCondition(B.CreateAnd(CheckBI->getCondition(), WC,
76                                      "exiplicit_guard_cond"));
77    assert(isWidenableBranch(CheckBI) && "sanity check");
78  }
79}
80
81
82void llvm::widenWidenableBranch(BranchInst *WidenableBR, Value *NewCond) {
83  assert(isWidenableBranch(WidenableBR) && "precondition");
84
85  // The tempting trivially option is to produce something like this:
86  // br (and oldcond, newcond) where oldcond is assumed to contain a widenable
87  // condition, but that doesn't match the pattern parseWidenableBranch expects
88  // so we have to be more sophisticated.
89
90  Use *C, *WC;
91  BasicBlock *IfTrueBB, *IfFalseBB;
92  parseWidenableBranch(WidenableBR, C, WC, IfTrueBB, IfFalseBB);
93  if (!C) {
94    // br (wc()), ... form
95    IRBuilder<> B(WidenableBR);
96    WidenableBR->setCondition(B.CreateAnd(NewCond, WC->get()));
97  } else {
98    // br (wc & C), ... form
99    IRBuilder<> B(WidenableBR);
100    C->set(B.CreateAnd(NewCond, C->get()));
101    Instruction *WCAnd = cast<Instruction>(WidenableBR->getCondition());
102    // Condition is only guaranteed to dominate branch
103    WCAnd->moveBefore(WidenableBR);
104  }
105  assert(isWidenableBranch(WidenableBR) && "preserve widenabiliy");
106}
107
108void llvm::setWidenableBranchCond(BranchInst *WidenableBR, Value *NewCond) {
109  assert(isWidenableBranch(WidenableBR) && "precondition");
110
111  Use *C, *WC;
112  BasicBlock *IfTrueBB, *IfFalseBB;
113  parseWidenableBranch(WidenableBR, C, WC, IfTrueBB, IfFalseBB);
114  if (!C) {
115    // br (wc()), ... form
116    IRBuilder<> B(WidenableBR);
117    WidenableBR->setCondition(B.CreateAnd(NewCond, WC->get()));
118  } else {
119    // br (wc & C), ... form
120    Instruction *WCAnd = cast<Instruction>(WidenableBR->getCondition());
121    // Condition is only guaranteed to dominate branch
122    WCAnd->moveBefore(WidenableBR);
123    C->set(NewCond);
124  }
125  assert(isWidenableBranch(WidenableBR) && "preserve widenabiliy");
126}
127