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().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 }
98