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