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