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 "WebAssemblyTargetMachine.h"
17 #include "llvm/CodeGen/MachineInstr.h"
18 #include "llvm/CodeGen/MachineLoopInfo.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/MC/MCContext.h"
21 using namespace llvm;
22
23 // Function names in libc++abi and libunwind
24 const char *const WebAssembly::CxaBeginCatchFn = "__cxa_begin_catch";
25 const char *const WebAssembly::CxaRethrowFn = "__cxa_rethrow";
26 const char *const WebAssembly::StdTerminateFn = "_ZSt9terminatev";
27 const char *const WebAssembly::PersonalityWrapperFn =
28 "_Unwind_Wasm_CallPersonality";
29
30 /// Test whether MI is a child of some other node in an expression tree.
isChild(const MachineInstr & MI,const WebAssemblyFunctionInfo & MFI)31 bool WebAssembly::isChild(const MachineInstr &MI,
32 const WebAssemblyFunctionInfo &MFI) {
33 if (MI.getNumOperands() == 0)
34 return false;
35 const MachineOperand &MO = MI.getOperand(0);
36 if (!MO.isReg() || MO.isImplicit() || !MO.isDef())
37 return false;
38 Register Reg = MO.getReg();
39 return Reg.isVirtual() && MFI.isVRegStackified(Reg);
40 }
41
mayThrow(const MachineInstr & MI)42 bool WebAssembly::mayThrow(const MachineInstr &MI) {
43 switch (MI.getOpcode()) {
44 case WebAssembly::THROW:
45 case WebAssembly::THROW_S:
46 case WebAssembly::RETHROW:
47 case WebAssembly::RETHROW_S:
48 return true;
49 }
50 if (isCallIndirect(MI.getOpcode()))
51 return true;
52 if (!MI.isCall())
53 return false;
54
55 const MachineOperand &MO = getCalleeOp(MI);
56 assert(MO.isGlobal() || MO.isSymbol());
57
58 if (MO.isSymbol()) {
59 // Some intrinsics are lowered to calls to external symbols, which are then
60 // lowered to calls to library functions. Most of libcalls don't throw, but
61 // we only list some of them here now.
62 // TODO Consider adding 'nounwind' info in TargetLowering::CallLoweringInfo
63 // instead for more accurate info.
64 const char *Name = MO.getSymbolName();
65 if (strcmp(Name, "memcpy") == 0 || strcmp(Name, "memmove") == 0 ||
66 strcmp(Name, "memset") == 0)
67 return false;
68 return true;
69 }
70
71 const auto *F = dyn_cast<Function>(MO.getGlobal());
72 if (!F)
73 return true;
74 if (F->doesNotThrow())
75 return false;
76 // These functions never throw
77 if (F->getName() == CxaBeginCatchFn || F->getName() == PersonalityWrapperFn ||
78 F->getName() == StdTerminateFn)
79 return false;
80
81 // TODO Can we exclude call instructions that are marked as 'nounwind' in the
82 // original LLVm IR? (Even when the callee may throw)
83 return true;
84 }
85
getCalleeOp(const MachineInstr & MI)86 const MachineOperand &WebAssembly::getCalleeOp(const MachineInstr &MI) {
87 switch (MI.getOpcode()) {
88 case WebAssembly::CALL:
89 case WebAssembly::CALL_S:
90 case WebAssembly::RET_CALL:
91 case WebAssembly::RET_CALL_S:
92 return MI.getOperand(MI.getNumExplicitDefs());
93 case WebAssembly::CALL_INDIRECT:
94 case WebAssembly::CALL_INDIRECT_S:
95 case WebAssembly::RET_CALL_INDIRECT:
96 case WebAssembly::RET_CALL_INDIRECT_S:
97 return MI.getOperand(MI.getNumExplicitOperands() - 1);
98 default:
99 llvm_unreachable("Not a call instruction");
100 }
101 }
102
getOrCreateFunctionTableSymbol(MCContext & Ctx,const WebAssemblySubtarget * Subtarget)103 MCSymbolWasm *WebAssembly::getOrCreateFunctionTableSymbol(
104 MCContext &Ctx, const WebAssemblySubtarget *Subtarget) {
105 StringRef Name = "__indirect_function_table";
106 MCSymbolWasm *Sym = cast_or_null<MCSymbolWasm>(Ctx.lookupSymbol(Name));
107 if (Sym) {
108 if (!Sym->isFunctionTable())
109 Ctx.reportError(SMLoc(), "symbol is not a wasm funcref table");
110 } else {
111 bool is64 = Subtarget && Subtarget->getTargetTriple().isArch64Bit();
112 Sym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(Name));
113 Sym->setFunctionTable(is64);
114 // The default function table is synthesized by the linker.
115 Sym->setUndefined();
116 }
117 // MVP object files can't have symtab entries for tables.
118 if (!(Subtarget && Subtarget->hasReferenceTypes()))
119 Sym->setOmitFromLinkingSection();
120 return Sym;
121 }
122
getOrCreateFuncrefCallTableSymbol(MCContext & Ctx,const WebAssemblySubtarget * Subtarget)123 MCSymbolWasm *WebAssembly::getOrCreateFuncrefCallTableSymbol(
124 MCContext &Ctx, const WebAssemblySubtarget *Subtarget) {
125 StringRef Name = "__funcref_call_table";
126 MCSymbolWasm *Sym = cast_or_null<MCSymbolWasm>(Ctx.lookupSymbol(Name));
127 if (Sym) {
128 if (!Sym->isFunctionTable())
129 Ctx.reportError(SMLoc(), "symbol is not a wasm funcref table");
130 } else {
131 Sym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(Name));
132
133 // Setting Weak ensure only one table is left after linking when multiple
134 // modules define the table.
135 Sym->setWeak(true);
136
137 wasm::WasmLimits Limits = {0, 1, 1};
138 wasm::WasmTableType TableType = {wasm::ValType::FUNCREF, Limits};
139 Sym->setType(wasm::WASM_SYMBOL_TYPE_TABLE);
140 Sym->setTableType(TableType);
141 }
142 // MVP object files can't have symtab entries for tables.
143 if (!(Subtarget && Subtarget->hasReferenceTypes()))
144 Sym->setOmitFromLinkingSection();
145 return Sym;
146 }
147
148 // Find a catch instruction from an EH pad.
findCatch(MachineBasicBlock * EHPad)149 MachineInstr *WebAssembly::findCatch(MachineBasicBlock *EHPad) {
150 assert(EHPad->isEHPad());
151 auto Pos = EHPad->begin();
152 // Skip any label or debug instructions. Also skip 'end' marker instructions
153 // that may exist after marker placement in CFGStackify.
154 while (Pos != EHPad->end() &&
155 (Pos->isLabel() || Pos->isDebugInstr() || isMarker(Pos->getOpcode())))
156 Pos++;
157 if (Pos != EHPad->end() && WebAssembly::isCatch(Pos->getOpcode()))
158 return &*Pos;
159 return nullptr;
160 }
161
getCopyOpcodeForRegClass(const TargetRegisterClass * RC)162 unsigned WebAssembly::getCopyOpcodeForRegClass(const TargetRegisterClass *RC) {
163 assert(RC != nullptr);
164 switch (RC->getID()) {
165 case WebAssembly::I32RegClassID:
166 return WebAssembly::COPY_I32;
167 case WebAssembly::I64RegClassID:
168 return WebAssembly::COPY_I64;
169 case WebAssembly::F32RegClassID:
170 return WebAssembly::COPY_F32;
171 case WebAssembly::F64RegClassID:
172 return WebAssembly::COPY_F64;
173 case WebAssembly::V128RegClassID:
174 return WebAssembly::COPY_V128;
175 case WebAssembly::FUNCREFRegClassID:
176 return WebAssembly::COPY_FUNCREF;
177 case WebAssembly::EXTERNREFRegClassID:
178 return WebAssembly::COPY_EXTERNREF;
179 case WebAssembly::EXNREFRegClassID:
180 return WebAssembly::COPY_EXNREF;
181 default:
182 llvm_unreachable("Unexpected register class");
183 }
184 }
185
canLowerMultivalueReturn(const WebAssemblySubtarget * Subtarget)186 bool WebAssembly::canLowerMultivalueReturn(
187 const WebAssemblySubtarget *Subtarget) {
188 const auto &TM = static_cast<const WebAssemblyTargetMachine &>(
189 Subtarget->getTargetLowering()->getTargetMachine());
190 return Subtarget->hasMultivalue() && TM.usesMultivalueABI();
191 }
192
canLowerReturn(size_t ResultSize,const WebAssemblySubtarget * Subtarget)193 bool WebAssembly::canLowerReturn(size_t ResultSize,
194 const WebAssemblySubtarget *Subtarget) {
195 return ResultSize <= 1 || canLowerMultivalueReturn(Subtarget);
196 }
197