llvm/lib/Target/WebAssembly/WebAssemblySetP2AlignOperands.cpp

   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<MachineBlockFrequencyInfoWrapperPass>();
  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().operands()[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 }