llvm/lib/Target/X86/X86MacroFusion.cpp

   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
  21 using namespace llvm;
  22
  23 static X86::FirstMacroFusionInstKind classifyFirst(const MachineInstr &MI) {
  24   return X86::classifyFirstOpcodeInMacroFusion(MI.getOpcode());
  25 }
  26
  27 static 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.
  35 static 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(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(*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(TestKind, BranchKind);
  63   }
  64
  65   llvm_unreachable("unknown fusion type");
  66 }
  67
  68 namespace llvm {
  69
  70 std::unique_ptr<ScheduleDAGMutation> createX86MacroFusionDAGMutation() {
  71   return createMacroFusionDAGMutation(shouldScheduleAdjacent,
  72                                       /*BranchOnly=*/true);
  73 }
  74
  75 } // end namespace llvm