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      1 //=- WebAssemblySetP2AlignOperands.cpp - Set alignments on loads and stores -=//
      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
     10 /// This file sets the p2align operands on load and store instructions.
     11 ///
     12 //===----------------------------------------------------------------------===//
     13 
     14 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
     15 #include "WebAssembly.h"
     16 #include "WebAssemblyInstrInfo.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   StringRef 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 INITIALIZE_PASS(WebAssemblySetP2AlignOperands, DEBUG_TYPE,
     50                 "Set the p2align operands for WebAssembly loads and stores",
     51                 false, false)
     52 
     53 FunctionPass *llvm::createWebAssemblySetP2AlignOperands() {
     54   return new WebAssemblySetP2AlignOperands();
     55 }
     56 
     57 static void rewriteP2Align(MachineInstr &MI, unsigned OperandNo) {
     58   assert(MI.getOperand(OperandNo).getImm() == 0 &&
     59          "ISel should set p2align operands to 0");
     60   assert(MI.hasOneMemOperand() &&
     61          "Load and store instructions have exactly one mem operand");
     62   assert((*MI.memoperands_begin())->getSize() ==
     63              (UINT64_C(1) << WebAssembly::GetDefaultP2Align(MI.getOpcode())) &&
     64          "Default p2align value should be natural");
     65   assert(MI.getDesc().OpInfo[OperandNo].OperandType ==
     66              WebAssembly::OPERAND_P2ALIGN &&
     67          "Load and store instructions should have a p2align operand");
     68   uint64_t P2Align = Log2((*MI.memoperands_begin())->getAlign());
     69 
     70   // WebAssembly does not currently support supernatural alignment.
     71   P2Align = std::min(P2Align,
     72                      uint64_t(WebAssembly::GetDefaultP2Align(MI.getOpcode())));
     73 
     74   MI.getOperand(OperandNo).setImm(P2Align);
     75 }
     76 
     77 bool WebAssemblySetP2AlignOperands::runOnMachineFunction(MachineFunction &MF) {
     78   LLVM_DEBUG({
     79     dbgs() << "********** Set p2align Operands **********\n"
     80            << "********** Function: " << MF.getName() << '\n';
     81   });
     82 
     83   bool Changed = false;
     84 
     85   for (auto &MBB : MF) {
     86     for (auto &MI : MBB) {
     87       int16_t P2AlignOpNum = WebAssembly::getNamedOperandIdx(
     88           MI.getOpcode(), WebAssembly::OpName::p2align);
     89       if (P2AlignOpNum != -1) {
     90         rewriteP2Align(MI, P2AlignOpNum);
     91         Changed = true;
     92       }
     93     }
     94   }
     95 
     96   return Changed;
     97 }
     98