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//- X86Insertwait.cpp - Strict-Fp:Insert wait instruction X87 instructions --//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file defines the pass which insert x86 wait instructions after each
// X87 instructions when strict float is enabled.
//
// The logic to insert a wait instruction after an X87 instruction is as below:
// 1. If the X87 instruction don't raise float exception nor is a load/store
// instruction, or is a x87 control instruction, don't insert wait.
// 2. If the X87 instruction is an instruction which the following instruction
// is an X87 exception synchronizing X87 instruction, don't insert wait.
// 3. For other situations, insert wait instruction.
//
//===----------------------------------------------------------------------===//
#include "X86.h"
#include "X86InstrInfo.h"
#include "X86Subtarget.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
#define DEBUG_TYPE "x86-insert-wait"
namespace {
class WaitInsert : public MachineFunctionPass {
public:
static char ID;
WaitInsert() : MachineFunctionPass(ID) {}
bool runOnMachineFunction(MachineFunction &MF) override;
StringRef getPassName() const override {
return "X86 insert wait instruction";
}
};
} // namespace
char WaitInsert::ID = 0;
FunctionPass *llvm::createX86InsertX87waitPass() { return new WaitInsert(); }
/// Return true if the Reg is X87 register.
static bool isX87Reg(unsigned Reg) {
return (Reg == X86::FPCW || Reg == X86::FPSW ||
(Reg >= X86::ST0 && Reg <= X86::ST7));
}
/// check if the instruction is X87 instruction
static bool isX87Instruction(MachineInstr &MI) {
for (const MachineOperand &MO : MI.operands()) {
if (!MO.isReg())
continue;
if (isX87Reg(MO.getReg()))
return true;
}
return false;
}
static bool isX87ControlInstruction(MachineInstr &MI) {
switch (MI.getOpcode()) {
case X86::FNINIT:
case X86::FLDCW16m:
case X86::FNSTCW16m:
case X86::FNSTSW16r:
case X86::FNSTSWm:
case X86::FNCLEX:
case X86::FLDENVm:
case X86::FSTENVm:
case X86::FRSTORm:
case X86::FSAVEm:
case X86::FINCSTP:
case X86::FDECSTP:
case X86::FFREE:
case X86::FFREEP:
case X86::FNOP:
case X86::WAIT:
return true;
default:
return false;
}
}
static bool isX87NonWaitingControlInstruction(MachineInstr &MI) {
// a few special control instructions don't perform a wait operation
switch (MI.getOpcode()) {
case X86::FNINIT:
case X86::FNSTSW16r:
case X86::FNSTSWm:
case X86::FNSTCW16m:
case X86::FNCLEX:
return true;
default:
return false;
}
}
bool WaitInsert::runOnMachineFunction(MachineFunction &MF) {
if (!MF.getFunction().hasFnAttribute(Attribute::StrictFP))
return false;
const X86Subtarget &ST = MF.getSubtarget<X86Subtarget>();
const X86InstrInfo *TII = ST.getInstrInfo();
bool Changed = false;
for (MachineBasicBlock &MBB : MF) {
for (MachineBasicBlock::iterator MI = MBB.begin(); MI != MBB.end(); ++MI) {
// Jump non X87 instruction.
if (!isX87Instruction(*MI))
continue;
// If the instruction instruction neither has float exception nor is
// a load/store instruction, or the instruction is x87 control
// instruction, do not insert wait.
if (!(MI->mayRaiseFPException() || MI->mayLoadOrStore()) ||
isX87ControlInstruction(*MI))
continue;
// If the following instruction is an X87 instruction and isn't an X87
// non-waiting control instruction, we can omit insert wait instruction.
MachineBasicBlock::iterator AfterMI = std::next(MI);
if (AfterMI != MBB.end() && isX87Instruction(*AfterMI) &&
!isX87NonWaitingControlInstruction(*AfterMI))
continue;
BuildMI(MBB, AfterMI, MI->getDebugLoc(), TII->get(X86::WAIT));
LLVM_DEBUG(dbgs() << "\nInsert wait after:\t" << *MI);
// Jump the newly inserting wait
++MI;
Changed = true;
}
}
return Changed;
}
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