lib/Target/WebAssembly/WebAssemblyUtilities.cpp

   1 //===-- WebAssemblyUtilities.cpp - WebAssembly Utility Functions ----------===//
   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 implements several utility functions for WebAssembly.
  11 ///
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "WebAssemblyUtilities.h"
  15 #include "WebAssemblyMachineFunctionInfo.h"
  16 #include "llvm/CodeGen/MachineInstr.h"
  17 #include "llvm/CodeGen/MachineLoopInfo.h"
  18 using namespace llvm;
  19
  20 const char *const WebAssembly::ClangCallTerminateFn = "__clang_call_terminate";
  21 const char *const WebAssembly::CxaBeginCatchFn = "__cxa_begin_catch";
  22 const char *const WebAssembly::CxaRethrowFn = "__cxa_rethrow";
  23 const char *const WebAssembly::StdTerminateFn = "_ZSt9terminatev";
  24 const char *const WebAssembly::PersonalityWrapperFn =
  25     "_Unwind_Wasm_CallPersonality";
  26
  27 /// Test whether MI is a child of some other node in an expression tree.
  28 bool WebAssembly::isChild(const MachineInstr &MI,
  29                           const WebAssemblyFunctionInfo &MFI) {
  30   if (MI.getNumOperands() == 0)
  31     return false;
  32   const MachineOperand &MO = MI.getOperand(0);
  33   if (!MO.isReg() || MO.isImplicit() || !MO.isDef())
  34     return false;
  35   Register Reg = MO.getReg();
  36   return Register::isVirtualRegister(Reg) && MFI.isVRegStackified(Reg);
  37 }
  38
  39 bool WebAssembly::mayThrow(const MachineInstr &MI) {
  40   switch (MI.getOpcode()) {
  41   case WebAssembly::THROW:
  42   case WebAssembly::THROW_S:
  43   case WebAssembly::RETHROW:
  44   case WebAssembly::RETHROW_S:
  45     return true;
  46   }
  47   if (isCallIndirect(MI.getOpcode()))
  48     return true;
  49   if (!MI.isCall())
  50     return false;
  51
  52   const MachineOperand &MO = MI.getOperand(getCalleeOpNo(MI.getOpcode()));
  53   assert(MO.isGlobal() || MO.isSymbol());
  54
  55   if (MO.isSymbol()) {
  56     // Some intrinsics are lowered to calls to external symbols, which are then
  57     // lowered to calls to library functions. Most of libcalls don't throw, but
  58     // we only list some of them here now.
  59     // TODO Consider adding 'nounwind' info in TargetLowering::CallLoweringInfo
  60     // instead for more accurate info.
  61     const char *Name = MO.getSymbolName();
  62     if (strcmp(Name, "memcpy") == 0 || strcmp(Name, "memmove") == 0 ||
  63         strcmp(Name, "memset") == 0)
  64       return false;
  65     return true;
  66   }
  67
  68   const auto *F = dyn_cast<Function>(MO.getGlobal());
  69   if (!F)
  70     return true;
  71   if (F->doesNotThrow())
  72     return false;
  73   // These functions never throw
  74   if (F->getName() == CxaBeginCatchFn || F->getName() == PersonalityWrapperFn ||
  75       F->getName() == ClangCallTerminateFn || F->getName() == StdTerminateFn)
  76     return false;
  77
  78   // TODO Can we exclude call instructions that are marked as 'nounwind' in the
  79   // original LLVm IR? (Even when the callee may throw)
  80   return true;
  81 }