xref: /llvm-project/llvm/lib/Target/WebAssembly/WebAssemblySetP2AlignOperands.cpp (revision 43570a2841e2a8f1efd00503beee751cc1e72513)
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 "llvm/CodeGen/MachineBlockFrequencyInfo.h"
18 #include "llvm/CodeGen/MachineMemOperand.h"
19 #include "llvm/CodeGen/Passes.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Support/raw_ostream.h"
22 using namespace llvm;
23 
24 #define DEBUG_TYPE "wasm-set-p2align-operands"
25 
26 namespace {
27 class WebAssemblySetP2AlignOperands final : public MachineFunctionPass {
28 public:
29   static char ID; // Pass identification, replacement for typeid
30   WebAssemblySetP2AlignOperands() : MachineFunctionPass(ID) {}
31 
32   StringRef getPassName() const override {
33     return "WebAssembly Set p2align Operands";
34   }
35 
36   void getAnalysisUsage(AnalysisUsage &AU) const override {
37     AU.setPreservesCFG();
38     AU.addPreserved<MachineBlockFrequencyInfoWrapperPass>();
39     AU.addPreservedID(MachineDominatorsID);
40     MachineFunctionPass::getAnalysisUsage(AU);
41   }
42 
43   bool runOnMachineFunction(MachineFunction &MF) override;
44 };
45 } // end anonymous namespace
46 
47 char WebAssemblySetP2AlignOperands::ID = 0;
48 INITIALIZE_PASS(WebAssemblySetP2AlignOperands, DEBUG_TYPE,
49                 "Set the p2align operands for WebAssembly loads and stores",
50                 false, false)
51 
52 FunctionPass *llvm::createWebAssemblySetP2AlignOperands() {
53   return new WebAssemblySetP2AlignOperands();
54 }
55 
56 static void rewriteP2Align(MachineInstr &MI, unsigned OperandNo) {
57   assert(MI.getOperand(OperandNo).getImm() == 0 &&
58          "ISel should set p2align operands to 0");
59   assert(MI.hasOneMemOperand() &&
60          "Load and store instructions have exactly one mem operand");
61   assert((*MI.memoperands_begin())->getSize() ==
62              (UINT64_C(1) << WebAssembly::GetDefaultP2Align(MI.getOpcode())) &&
63          "Default p2align value should be natural");
64   assert(MI.getDesc().operands()[OperandNo].OperandType ==
65              WebAssembly::OPERAND_P2ALIGN &&
66          "Load and store instructions should have a p2align operand");
67   uint64_t P2Align = Log2((*MI.memoperands_begin())->getAlign());
68 
69   // WebAssembly does not currently support supernatural alignment.
70   P2Align = std::min(P2Align,
71                      uint64_t(WebAssembly::GetDefaultP2Align(MI.getOpcode())));
72 
73   MI.getOperand(OperandNo).setImm(P2Align);
74 }
75 
76 bool WebAssemblySetP2AlignOperands::runOnMachineFunction(MachineFunction &MF) {
77   LLVM_DEBUG({
78     dbgs() << "********** Set p2align Operands **********\n"
79            << "********** Function: " << MF.getName() << '\n';
80   });
81 
82   bool Changed = false;
83 
84   for (auto &MBB : MF) {
85     for (auto &MI : MBB) {
86       int16_t P2AlignOpNum = WebAssembly::getNamedOperandIdx(
87           MI.getOpcode(), WebAssembly::OpName::p2align);
88       if (P2AlignOpNum != -1) {
89         rewriteP2Align(MI, P2AlignOpNum);
90         Changed = true;
91       }
92     }
93   }
94 
95   return Changed;
96 }
97