1 //===- WebAssemblyTargetMachine.cpp - Define TargetMachine for WebAssembly -==//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 /// \brief This file defines the WebAssembly-specific subclass of TargetMachine.
13 //===----------------------------------------------------------------------===//
15 #include "WebAssembly.h"
16 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
17 #include "WebAssemblyTargetMachine.h"
18 #include "WebAssemblyTargetObjectFile.h"
19 #include "WebAssemblyTargetTransformInfo.h"
20 #include "llvm/CodeGen/MachineFunctionPass.h"
21 #include "llvm/CodeGen/Passes.h"
22 #include "llvm/CodeGen/RegAllocRegistry.h"
23 #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
24 #include "llvm/IR/Function.h"
25 #include "llvm/Support/CommandLine.h"
26 #include "llvm/Support/TargetRegistry.h"
27 #include "llvm/Target/TargetOptions.h"
28 #include "llvm/Transforms/Scalar.h"
31 #define DEBUG_TYPE "wasm"
33 extern "C" void LLVMInitializeWebAssemblyTarget() {
34 // Register the target.
35 RegisterTargetMachine<WebAssemblyTargetMachine> X(TheWebAssemblyTarget32);
36 RegisterTargetMachine<WebAssemblyTargetMachine> Y(TheWebAssemblyTarget64);
39 //===----------------------------------------------------------------------===//
40 // WebAssembly Lowering public interface.
41 //===----------------------------------------------------------------------===//
43 /// Create an WebAssembly architecture model.
45 WebAssemblyTargetMachine::WebAssemblyTargetMachine(
46 const Target &T, const Triple &TT, StringRef CPU, StringRef FS,
47 const TargetOptions &Options, Reloc::Model RM, CodeModel::Model CM,
49 : LLVMTargetMachine(T, TT.isArch64Bit() ? "e-p:64:64-i64:64-n32:64-S128"
50 : "e-p:32:32-i64:64-n32:64-S128",
51 TT, CPU, FS, Options, RM, CM, OL),
52 TLOF(make_unique<WebAssemblyTargetObjectFile>()) {
53 // WebAssembly type-checks expressions, but a noreturn function with a return
54 // type that doesn't match the context will cause a check failure. So we lower
55 // LLVM 'unreachable' to ISD::TRAP and then lower that to WebAssembly's
56 // 'unreachable' expression which is meant for that case.
57 this->Options.TrapUnreachable = true;
61 // We need a reducible CFG, so disable some optimizations which tend to
62 // introduce irreducibility.
63 setRequiresStructuredCFG(true);
66 WebAssemblyTargetMachine::~WebAssemblyTargetMachine() {}
68 const WebAssemblySubtarget *
69 WebAssemblyTargetMachine::getSubtargetImpl(const Function &F) const {
70 Attribute CPUAttr = F.getFnAttribute("target-cpu");
71 Attribute FSAttr = F.getFnAttribute("target-features");
73 std::string CPU = !CPUAttr.hasAttribute(Attribute::None)
74 ? CPUAttr.getValueAsString().str()
76 std::string FS = !FSAttr.hasAttribute(Attribute::None)
77 ? FSAttr.getValueAsString().str()
80 auto &I = SubtargetMap[CPU + FS];
82 // This needs to be done before we create a new subtarget since any
83 // creation will depend on the TM and the code generation flags on the
84 // function that reside in TargetOptions.
85 resetTargetOptions(F);
86 I = llvm::make_unique<WebAssemblySubtarget>(TargetTriple, CPU, FS, *this);
92 /// WebAssembly Code Generator Pass Configuration Options.
93 class WebAssemblyPassConfig final : public TargetPassConfig {
95 WebAssemblyPassConfig(WebAssemblyTargetMachine *TM, PassManagerBase &PM)
96 : TargetPassConfig(TM, PM) {}
98 WebAssemblyTargetMachine &getWebAssemblyTargetMachine() const {
99 return getTM<WebAssemblyTargetMachine>();
102 FunctionPass *createTargetRegisterAllocator(bool) override;
104 void addIRPasses() override;
105 bool addInstSelector() override;
106 bool addILPOpts() override;
107 void addPreRegAlloc() override;
108 void addPostRegAlloc() override;
109 void addPreEmitPass() override;
111 } // end anonymous namespace
113 TargetIRAnalysis WebAssemblyTargetMachine::getTargetIRAnalysis() {
114 return TargetIRAnalysis([this](const Function &F) {
115 return TargetTransformInfo(WebAssemblyTTIImpl(this, F));
120 WebAssemblyTargetMachine::createPassConfig(PassManagerBase &PM) {
121 return new WebAssemblyPassConfig(this, PM);
124 FunctionPass *WebAssemblyPassConfig::createTargetRegisterAllocator(bool) {
125 return nullptr; // No reg alloc
128 //===----------------------------------------------------------------------===//
129 // The following functions are called from lib/CodeGen/Passes.cpp to modify
130 // the CodeGen pass sequence.
131 //===----------------------------------------------------------------------===//
133 void WebAssemblyPassConfig::addIRPasses() {
134 if (TM->Options.ThreadModel == ThreadModel::Single)
135 // In "single" mode, atomics get lowered to non-atomics.
136 addPass(createLowerAtomicPass());
138 // Expand some atomic operations. WebAssemblyTargetLowering has hooks which
139 // control specifically what gets lowered.
140 addPass(createAtomicExpandPass(TM));
142 // Optimize "returned" function attributes.
143 addPass(createWebAssemblyOptimizeReturned());
145 TargetPassConfig::addIRPasses();
148 bool WebAssemblyPassConfig::addInstSelector() {
150 createWebAssemblyISelDag(getWebAssemblyTargetMachine(), getOptLevel()));
154 bool WebAssemblyPassConfig::addILPOpts() { return true; }
156 void WebAssemblyPassConfig::addPreRegAlloc() {
157 // Prepare store instructions for register stackifying.
158 addPass(createWebAssemblyStoreResults());
160 // Mark registers as representing wasm's expression stack.
161 addPass(createWebAssemblyRegStackify());
164 void WebAssemblyPassConfig::addPostRegAlloc() {
165 // TODO: The following CodeGen passes don't currently support code containing
166 // virtual registers. Consider removing their restrictions and re-enabling
169 // Fails with: Regalloc must assign all vregs.
170 disablePass(&PrologEpilogCodeInserterID);
171 // Fails with: should be run after register allocation.
172 disablePass(&MachineCopyPropagationID);
174 // TODO: Until we get ReverseBranchCondition support, MachineBlockPlacement
175 // can create ugly-looking control flow.
176 disablePass(&MachineBlockPlacementID);
178 // Run the register coloring pass to reduce the total number of registers.
179 addPass(createWebAssemblyRegColoring());
182 void WebAssemblyPassConfig::addPreEmitPass() {
183 // Put the CFG in structured form; insert BLOCK and LOOP markers.
184 addPass(createWebAssemblyCFGStackify());
186 // Create a mapping from LLVM CodeGen virtual registers to wasm registers.
187 addPass(createWebAssemblyRegNumbering());
189 // Perform the very last peephole optimizations on the code.
190 addPass(createWebAssemblyPeephole());