1//===- X86MacroFusion.cpp - X86 Macro Fusion ------------------------------===//
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//
9/// \file This file contains the X86 implementation of the DAG scheduling
10/// mutation to pair instructions back to back.
11//
12//===----------------------------------------------------------------------===//
13
14#include "X86MacroFusion.h"
15#include "MCTargetDesc/X86BaseInfo.h"
16#include "X86Subtarget.h"
17#include "llvm/CodeGen/MacroFusion.h"
18#include "llvm/CodeGen/ScheduleDAGMutation.h"
19#include "llvm/CodeGen/TargetInstrInfo.h"
20
21using namespace llvm;
22
23static X86::FirstMacroFusionInstKind classifyFirst(const MachineInstr &MI) {
24 return X86::classifyFirstOpcodeInMacroFusion(Opcode: MI.getOpcode());
25}
26
27static X86::SecondMacroFusionInstKind classifySecond(const MachineInstr &MI) {
28 X86::CondCode CC = X86::getCondFromBranch(MI);
29 return X86::classifySecondCondCodeInMacroFusion(CC);
30}
31
32/// Check if the instr pair, FirstMI and SecondMI, should be fused
33/// together. Given SecondMI, when FirstMI is unspecified, then check if
34/// SecondMI may be part of a fused pair at all.
35static bool shouldScheduleAdjacent(const TargetInstrInfo &TII,
36 const TargetSubtargetInfo &TSI,
37 const MachineInstr *FirstMI,
38 const MachineInstr &SecondMI) {
39 const X86Subtarget &ST = static_cast<const X86Subtarget &>(TSI);
40
41 // Check if this processor supports any kind of fusion.
42 if (!(ST.hasBranchFusion() || ST.hasMacroFusion()))
43 return false;
44
45 const X86::SecondMacroFusionInstKind BranchKind = classifySecond(MI: SecondMI);
46
47 if (BranchKind == X86::SecondMacroFusionInstKind::Invalid)
48 return false; // Second cannot be fused with anything.
49
50 if (FirstMI == nullptr)
51 return true; // We're only checking whether Second can be fused at all.
52
53 const X86::FirstMacroFusionInstKind TestKind = classifyFirst(MI: *FirstMI);
54
55 if (ST.hasBranchFusion()) {
56 // Branch fusion can merge CMP and TEST with all conditional jumps.
57 return (TestKind == X86::FirstMacroFusionInstKind::Cmp ||
58 TestKind == X86::FirstMacroFusionInstKind::Test);
59 }
60
61 if (ST.hasMacroFusion()) {
62 return X86::isMacroFused(FirstKind: TestKind, SecondKind: BranchKind);
63 }
64
65 llvm_unreachable("unknown fusion type");
66}
67
68namespace llvm {
69
70std::unique_ptr<ScheduleDAGMutation> createX86MacroFusionDAGMutation() {
71 return createMacroFusionDAGMutation(Predicates: shouldScheduleAdjacent,
72 /*BranchOnly=*/true);
73}
74
75} // end namespace llvm
76