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      1 //=- WebAssemblySetP2AlignOperands.cpp - Set alignments on loads and stores -=//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 ///
     10 /// \file
     11 /// \brief This file sets the p2align operands on load and store instructions.
     12 ///
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "WebAssembly.h"
     16 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
     17 #include "WebAssemblyMachineFunctionInfo.h"
     18 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
     19 #include "llvm/CodeGen/MachineMemOperand.h"
     20 #include "llvm/CodeGen/Passes.h"
     21 #include "llvm/Support/Debug.h"
     22 #include "llvm/Support/raw_ostream.h"
     23 using namespace llvm;
     24 
     25 #define DEBUG_TYPE "wasm-set-p2align-operands"
     26 
     27 namespace {
     28 class WebAssemblySetP2AlignOperands final : public MachineFunctionPass {
     29 public:
     30   static char ID; // Pass identification, replacement for typeid
     31   WebAssemblySetP2AlignOperands() : MachineFunctionPass(ID) {}
     32 
     33   const char *getPassName() const override {
     34     return "WebAssembly Set p2align Operands";
     35   }
     36 
     37   void getAnalysisUsage(AnalysisUsage &AU) const override {
     38     AU.setPreservesCFG();
     39     AU.addPreserved<MachineBlockFrequencyInfo>();
     40     AU.addPreservedID(MachineDominatorsID);
     41     MachineFunctionPass::getAnalysisUsage(AU);
     42   }
     43 
     44   bool runOnMachineFunction(MachineFunction &MF) override;
     45 };
     46 } // end anonymous namespace
     47 
     48 char WebAssemblySetP2AlignOperands::ID = 0;
     49 FunctionPass *llvm::createWebAssemblySetP2AlignOperands() {
     50   return new WebAssemblySetP2AlignOperands();
     51 }
     52 
     53 bool WebAssemblySetP2AlignOperands::runOnMachineFunction(MachineFunction &MF) {
     54   DEBUG({
     55     dbgs() << "********** Set p2align Operands **********\n"
     56            << "********** Function: " << MF.getName() << '\n';
     57   });
     58 
     59   bool Changed = false;
     60 
     61   for (auto &MBB : MF) {
     62     for (auto &MI : MBB) {
     63       switch (MI.getOpcode()) {
     64       case WebAssembly::LOAD_I32:
     65       case WebAssembly::LOAD_I64:
     66       case WebAssembly::LOAD_F32:
     67       case WebAssembly::LOAD_F64:
     68       case WebAssembly::LOAD8_S_I32:
     69       case WebAssembly::LOAD8_U_I32:
     70       case WebAssembly::LOAD16_S_I32:
     71       case WebAssembly::LOAD16_U_I32:
     72       case WebAssembly::LOAD8_S_I64:
     73       case WebAssembly::LOAD8_U_I64:
     74       case WebAssembly::LOAD16_S_I64:
     75       case WebAssembly::LOAD16_U_I64:
     76       case WebAssembly::LOAD32_S_I64:
     77       case WebAssembly::LOAD32_U_I64:
     78       case WebAssembly::STORE_I32:
     79       case WebAssembly::STORE_I64:
     80       case WebAssembly::STORE_F32:
     81       case WebAssembly::STORE_F64:
     82       case WebAssembly::STORE8_I32:
     83       case WebAssembly::STORE16_I32:
     84       case WebAssembly::STORE8_I64:
     85       case WebAssembly::STORE16_I64:
     86       case WebAssembly::STORE32_I64: {
     87         assert(MI.getOperand(3).getImm() == 0 &&
     88                "ISel should set p2align operands to 0");
     89         assert(MI.hasOneMemOperand() &&
     90                "Load and store instructions have exactly one mem operand");
     91         assert((*MI.memoperands_begin())->getSize() ==
     92                    (UINT64_C(1)
     93                     << WebAssembly::GetDefaultP2Align(MI.getOpcode())) &&
     94                "Default p2align value should be natural");
     95         assert(MI.getDesc().OpInfo[3].OperandType ==
     96                    WebAssembly::OPERAND_P2ALIGN &&
     97                "Load and store instructions should have a p2align operand");
     98         uint64_t P2Align = Log2_64((*MI.memoperands_begin())->getAlignment());
     99 
    100         // WebAssembly does not currently support supernatural alignment.
    101         P2Align = std::min(
    102             P2Align, uint64_t(WebAssembly::GetDefaultP2Align(MI.getOpcode())));
    103 
    104         MI.getOperand(3).setImm(P2Align);
    105         break;
    106       }
    107       default:
    108         break;
    109       }
    110     }
    111   }
    112 
    113   return Changed;
    114 }
    115