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//===------------ MIRVRegNamerUtils.h - MIR VReg Renaming Utilities -------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// The purpose of these utilities is to abstract out parts of the MIRCanon pass
// that are responsible for renaming virtual registers with the purpose of
// sharing code with a MIRVRegNamer pass that could be the analog of the
// opt -instnamer pass.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_LIB_CODEGEN_MIRVREGNAMERUTILS_H
#define LLVM_LIB_CODEGEN_MIRVREGNAMERUTILS_H
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Support/raw_ostream.h"
#include <queue>
namespace llvm {
/// NamedVRegCursor - The cursor is an object that keeps track of what the next
/// vreg name should be. It does book keeping to determine when to skip the
/// index value and by how much, or if the next vreg name should be an increment
/// from the previous.
class NamedVRegCursor {
MachineRegisterInfo &MRI;
/// virtualVRegNumber - Book keeping of the last vreg position.
unsigned virtualVRegNumber;
/// SkipGapSize - Used to calculate a modulo amount to skip by after every
/// sequence of instructions starting from a given side-effecting
/// MachineInstruction for a given MachineBasicBlock. The general idea is that
/// for a given program compiled with two different opt pipelines, there
/// shouldn't be greater than SkipGapSize difference in how many vregs are in
/// play between the two and for every def-use graph of vregs we rename we
/// will round up to the next SkipGapSize'th number so that we have a high
/// change of landing on the same name for two given matching side-effects
/// for the two compilation outcomes.
const unsigned SkipGapSize;
/// RenamedInOtherBB - VRegs that we already renamed: ie breadcrumbs.
std::vector<Register> RenamedInOtherBB;
public:
NamedVRegCursor() = delete;
/// 1000 for the SkipGapSize was a good heuristic at the time of the writing
/// of the MIRCanonicalizerPass. Adjust as needed.
NamedVRegCursor(MachineRegisterInfo &MRI, unsigned SkipGapSize = 1000)
: MRI(MRI), virtualVRegNumber(0), SkipGapSize(SkipGapSize) {}
/// SkipGapSize - Skips modulo a gap value of indices. Indices are used to
/// produce the next vreg name.
void skipVRegs();
unsigned getVirtualVReg() const { return virtualVRegNumber; }
/// incrementVirtualVReg - This increments an index value that us used to
/// create a new vreg name. This is not a Register.
unsigned incrementVirtualVReg(unsigned incr = 1) {
virtualVRegNumber += incr;
return virtualVRegNumber;
}
/// createVirtualRegister - Given an existing vreg, create a named vreg to
/// take its place.
unsigned createVirtualRegister(unsigned VReg);
/// renameVRegs - For a given MachineBasicBlock, scan for side-effecting
/// instructions, walk the def-use from each side-effecting root (in sorted
/// root order) and rename the encountered vregs in the def-use graph in a
/// canonical ordering. This method maintains book keeping for which vregs
/// were already renamed in RenamedInOtherBB.
// @return changed
bool renameVRegs(MachineBasicBlock *MBB);
};
} // namespace llvm
#endif
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