llvm/lib/CodeGen/ExpandLargeDivRem.cpp

   1 //===--- ExpandLargeDivRem.cpp - Expand large div/rem ---------------------===//
   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 // This pass expands div/rem instructions with a bitwidth above a threshold
  10 // into a call to auto-generated functions.
  11 // This is useful for targets like x86_64 that cannot lower divisions
  12 // with more than 128 bits or targets like x86_32 that cannot lower divisions
  13 // with more than 64 bits.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #include "llvm/CodeGen/ExpandLargeDivRem.h"
  18 #include "llvm/ADT/SmallVector.h"
  19 #include "llvm/ADT/StringExtras.h"
  20 #include "llvm/Analysis/GlobalsModRef.h"
  21 #include "llvm/CodeGen/Passes.h"
  22 #include "llvm/CodeGen/TargetLowering.h"
  23 #include "llvm/CodeGen/TargetPassConfig.h"
  24 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  25 #include "llvm/IR/IRBuilder.h"
  26 #include "llvm/IR/InstIterator.h"
  27 #include "llvm/IR/PassManager.h"
  28 #include "llvm/InitializePasses.h"
  29 #include "llvm/Pass.h"
  30 #include "llvm/Support/CommandLine.h"
  31 #include "llvm/Target/TargetMachine.h"
  32 #include "llvm/Transforms/Utils/IntegerDivision.h"
  33
  34 using namespace llvm;
  35
  36 static cl::opt<unsigned>
  37     ExpandDivRemBits("expand-div-rem-bits", cl::Hidden,
  38                      cl::init(llvm::IntegerType::MAX_INT_BITS),
  39                      cl::desc("div and rem instructions on integers with "
  40                               "more than <N> bits are expanded."));
  41
  42 static bool isConstantPowerOfTwo(llvm::Value *V, bool SignedOp) {
  43   auto *C = dyn_cast<ConstantInt>(V);
  44   if (!C)
  45     return false;
  46
  47   APInt Val = C->getValue();
  48   if (SignedOp && Val.isNegative())
  49     Val = -Val;
  50   return Val.isPowerOf2();
  51 }
  52
  53 static bool isSigned(unsigned int Opcode) {
  54   return Opcode == Instruction::SDiv || Opcode == Instruction::SRem;
  55 }
  56
  57 static bool runImpl(Function &F, const TargetLowering &TLI) {
  58   SmallVector<BinaryOperator *, 4> Replace;
  59   bool Modified = false;
  60
  61   unsigned MaxLegalDivRemBitWidth = TLI.getMaxDivRemBitWidthSupported();
  62   if (ExpandDivRemBits != llvm::IntegerType::MAX_INT_BITS)
  63     MaxLegalDivRemBitWidth = ExpandDivRemBits;
  64
  65   if (MaxLegalDivRemBitWidth >= llvm::IntegerType::MAX_INT_BITS)
  66     return false;
  67
  68   for (auto &I : instructions(F)) {
  69     switch (I.getOpcode()) {
  70     case Instruction::UDiv:
  71     case Instruction::SDiv:
  72     case Instruction::URem:
  73     case Instruction::SRem: {
  74       // TODO: This doesn't handle vectors.
  75       auto *IntTy = dyn_cast<IntegerType>(I.getType());
  76       if (!IntTy || IntTy->getIntegerBitWidth() <= MaxLegalDivRemBitWidth)
  77         continue;
  78
  79       // The backend has peephole optimizations for powers of two.
  80       if (isConstantPowerOfTwo(I.getOperand(1), isSigned(I.getOpcode())))
  81         continue;
  82
  83       Replace.push_back(&cast<BinaryOperator>(I));
  84       Modified = true;
  85       break;
  86     }
  87     default:
  88       break;
  89     }
  90   }
  91
  92   if (Replace.empty())
  93     return false;
  94
  95   while (!Replace.empty()) {
  96     BinaryOperator *I = Replace.pop_back_val();
  97
  98     if (I->getOpcode() == Instruction::UDiv ||
  99         I->getOpcode() == Instruction::SDiv) {
 100       expandDivision(I);
 101     } else {
 102       expandRemainder(I);
 103     }
 104   }
 105
 106   return Modified;
 107 }
 108
 109 namespace {
 110 class ExpandLargeDivRemLegacyPass : public FunctionPass {
 111 public:
 112   static char ID;
 113
 114   ExpandLargeDivRemLegacyPass() : FunctionPass(ID) {
 115     initializeExpandLargeDivRemLegacyPassPass(*PassRegistry::getPassRegistry());
 116   }
 117
 118   bool runOnFunction(Function &F) override {
 119     auto *TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
 120     auto *TLI = TM->getSubtargetImpl(F)->getTargetLowering();
 121     return runImpl(F, *TLI);
 122   }
 123
 124   void getAnalysisUsage(AnalysisUsage &AU) const override {
 125     AU.addRequired<TargetPassConfig>();
 126     AU.addPreserved<AAResultsWrapperPass>();
 127     AU.addPreserved<GlobalsAAWrapperPass>();
 128   }
 129 };
 130 } // namespace
 131
 132 PreservedAnalyses ExpandLargeDivRemPass::run(Function &F,
 133                                              FunctionAnalysisManager &FAM) {
 134   const TargetSubtargetInfo *STI = TM->getSubtargetImpl(F);
 135   return runImpl(F, *STI->getTargetLowering()) ? PreservedAnalyses::none()
 136                                                : PreservedAnalyses::all();
 137 }
 138
 139 char ExpandLargeDivRemLegacyPass::ID = 0;
 140 INITIALIZE_PASS_BEGIN(ExpandLargeDivRemLegacyPass, "expand-large-div-rem",
 141                       "Expand large div/rem", false, false)
 142 INITIALIZE_PASS_END(ExpandLargeDivRemLegacyPass, "expand-large-div-rem",
 143                     "Expand large div/rem", false, false)
 144
 145 FunctionPass *llvm::createExpandLargeDivRemPass() {
 146   return new ExpandLargeDivRemLegacyPass();
 147 }