1 //===- WebAssemblyTargetMachine.cpp - Define TargetMachine for WebAssembly -==//
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
7 //===----------------------------------------------------------------------===//
10 /// This file defines the WebAssembly-specific subclass of TargetMachine.
12 //===----------------------------------------------------------------------===//
14 #include "WebAssemblyTargetMachine.h"
15 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
16 #include "TargetInfo/WebAssemblyTargetInfo.h"
17 #include "WebAssembly.h"
18 #include "WebAssemblyMachineFunctionInfo.h"
19 #include "WebAssemblyTargetObjectFile.h"
20 #include "WebAssemblyTargetTransformInfo.h"
21 #include "llvm/CodeGen/MIRParser/MIParser.h"
22 #include "llvm/CodeGen/MachineFunctionPass.h"
23 #include "llvm/CodeGen/Passes.h"
24 #include "llvm/CodeGen/RegAllocRegistry.h"
25 #include "llvm/CodeGen/TargetPassConfig.h"
26 #include "llvm/IR/Function.h"
27 #include "llvm/Support/TargetRegistry.h"
28 #include "llvm/Target/TargetOptions.h"
29 #include "llvm/Transforms/Scalar.h"
30 #include "llvm/Transforms/Scalar/LowerAtomic.h"
31 #include "llvm/Transforms/Utils.h"
34 #define DEBUG_TYPE "wasm"
36 // Emscripten's asm.js-style exception handling
37 static cl::opt
<bool> EnableEmException(
38 "enable-emscripten-cxx-exceptions",
39 cl::desc("WebAssembly Emscripten-style exception handling"),
42 // Emscripten's asm.js-style setjmp/longjmp handling
43 static cl::opt
<bool> EnableEmSjLj(
44 "enable-emscripten-sjlj",
45 cl::desc("WebAssembly Emscripten-style setjmp/longjmp handling"),
48 extern "C" void LLVMInitializeWebAssemblyTarget() {
49 // Register the target.
50 RegisterTargetMachine
<WebAssemblyTargetMachine
> X(
51 getTheWebAssemblyTarget32());
52 RegisterTargetMachine
<WebAssemblyTargetMachine
> Y(
53 getTheWebAssemblyTarget64());
55 // Register backend passes
56 auto &PR
= *PassRegistry::getPassRegistry();
57 initializeWebAssemblyAddMissingPrototypesPass(PR
);
58 initializeWebAssemblyLowerEmscriptenEHSjLjPass(PR
);
59 initializeLowerGlobalDtorsPass(PR
);
60 initializeFixFunctionBitcastsPass(PR
);
61 initializeOptimizeReturnedPass(PR
);
62 initializeWebAssemblyArgumentMovePass(PR
);
63 initializeWebAssemblySetP2AlignOperandsPass(PR
);
64 initializeWebAssemblyReplacePhysRegsPass(PR
);
65 initializeWebAssemblyPrepareForLiveIntervalsPass(PR
);
66 initializeWebAssemblyOptimizeLiveIntervalsPass(PR
);
67 initializeWebAssemblyMemIntrinsicResultsPass(PR
);
68 initializeWebAssemblyRegStackifyPass(PR
);
69 initializeWebAssemblyRegColoringPass(PR
);
70 initializeWebAssemblyFixIrreducibleControlFlowPass(PR
);
71 initializeWebAssemblyLateEHPreparePass(PR
);
72 initializeWebAssemblyExceptionInfoPass(PR
);
73 initializeWebAssemblyCFGSortPass(PR
);
74 initializeWebAssemblyCFGStackifyPass(PR
);
75 initializeWebAssemblyExplicitLocalsPass(PR
);
76 initializeWebAssemblyLowerBrUnlessPass(PR
);
77 initializeWebAssemblyRegNumberingPass(PR
);
78 initializeWebAssemblyPeepholePass(PR
);
79 initializeWebAssemblyCallIndirectFixupPass(PR
);
82 //===----------------------------------------------------------------------===//
83 // WebAssembly Lowering public interface.
84 //===----------------------------------------------------------------------===//
86 static Reloc::Model
getEffectiveRelocModel(Optional
<Reloc::Model
> RM
,
89 // Default to static relocation model. This should always be more optimial
90 // than PIC since the static linker can determine all global addresses and
91 // assume direct function calls.
95 if (!TT
.isOSEmscripten()) {
96 // Relocation modes other than static are currently implemented in a way
97 // that only works for Emscripten, so disable them if we aren't targeting
105 /// Create an WebAssembly architecture model.
107 WebAssemblyTargetMachine::WebAssemblyTargetMachine(
108 const Target
&T
, const Triple
&TT
, StringRef CPU
, StringRef FS
,
109 const TargetOptions
&Options
, Optional
<Reloc::Model
> RM
,
110 Optional
<CodeModel::Model
> CM
, CodeGenOpt::Level OL
, bool JIT
)
111 : LLVMTargetMachine(T
,
112 TT
.isArch64Bit() ? "e-m:e-p:64:64-i64:64-n32:64-S128"
113 : "e-m:e-p:32:32-i64:64-n32:64-S128",
114 TT
, CPU
, FS
, Options
, getEffectiveRelocModel(RM
, TT
),
115 getEffectiveCodeModel(CM
, CodeModel::Large
), OL
),
116 TLOF(new WebAssemblyTargetObjectFile()) {
117 // WebAssembly type-checks instructions, but a noreturn function with a return
118 // type that doesn't match the context will cause a check failure. So we lower
119 // LLVM 'unreachable' to ISD::TRAP and then lower that to WebAssembly's
120 // 'unreachable' instructions which is meant for that case.
121 this->Options
.TrapUnreachable
= true;
123 // WebAssembly treats each function as an independent unit. Force
124 // -ffunction-sections, effectively, so that we can emit them independently.
125 this->Options
.FunctionSections
= true;
126 this->Options
.DataSections
= true;
127 this->Options
.UniqueSectionNames
= true;
131 // Note that we don't use setRequiresStructuredCFG(true). It disables
132 // optimizations than we're ok with, and want, such as critical edge
133 // splitting and tail merging.
136 WebAssemblyTargetMachine::~WebAssemblyTargetMachine() = default; // anchor.
138 const WebAssemblySubtarget
*
139 WebAssemblyTargetMachine::getSubtargetImpl(std::string CPU
,
140 std::string FS
) const {
141 auto &I
= SubtargetMap
[CPU
+ FS
];
143 I
= std::make_unique
<WebAssemblySubtarget
>(TargetTriple
, CPU
, FS
, *this);
148 const WebAssemblySubtarget
*
149 WebAssemblyTargetMachine::getSubtargetImpl(const Function
&F
) const {
150 Attribute CPUAttr
= F
.getFnAttribute("target-cpu");
151 Attribute FSAttr
= F
.getFnAttribute("target-features");
153 std::string CPU
= !CPUAttr
.hasAttribute(Attribute::None
)
154 ? CPUAttr
.getValueAsString().str()
156 std::string FS
= !FSAttr
.hasAttribute(Attribute::None
)
157 ? FSAttr
.getValueAsString().str()
160 // This needs to be done before we create a new subtarget since any
161 // creation will depend on the TM and the code generation flags on the
162 // function that reside in TargetOptions.
163 resetTargetOptions(F
);
165 return getSubtargetImpl(CPU
, FS
);
170 class CoalesceFeaturesAndStripAtomics final
: public ModulePass
{
171 // Take the union of all features used in the module and use it for each
172 // function individually, since having multiple feature sets in one module
173 // currently does not make sense for WebAssembly. If atomics are not enabled,
174 // also strip atomic operations and thread local storage.
176 WebAssemblyTargetMachine
*WasmTM
;
179 CoalesceFeaturesAndStripAtomics(WebAssemblyTargetMachine
*WasmTM
)
180 : ModulePass(ID
), WasmTM(WasmTM
) {}
182 bool runOnModule(Module
&M
) override
{
183 FeatureBitset Features
= coalesceFeatures(M
);
185 std::string FeatureStr
= getFeatureString(Features
);
187 replaceFeatures(F
, FeatureStr
);
189 bool StrippedAtomics
= false;
190 bool StrippedTLS
= false;
192 if (!Features
[WebAssembly::FeatureAtomics
])
193 StrippedAtomics
= stripAtomics(M
);
195 if (!Features
[WebAssembly::FeatureBulkMemory
])
196 StrippedTLS
= stripThreadLocals(M
);
198 if (StrippedAtomics
&& !StrippedTLS
)
199 stripThreadLocals(M
);
200 else if (StrippedTLS
&& !StrippedAtomics
)
203 recordFeatures(M
, Features
, StrippedAtomics
|| StrippedTLS
);
205 // Conservatively assume we have made some change
210 FeatureBitset
coalesceFeatures(const Module
&M
) {
211 FeatureBitset Features
=
213 ->getSubtargetImpl(WasmTM
->getTargetCPU(),
214 WasmTM
->getTargetFeatureString())
217 Features
|= WasmTM
->getSubtargetImpl(F
)->getFeatureBits();
221 std::string
getFeatureString(const FeatureBitset
&Features
) {
223 for (const SubtargetFeatureKV
&KV
: WebAssemblyFeatureKV
) {
224 if (Features
[KV
.Value
])
225 Ret
+= (StringRef("+") + KV
.Key
+ ",").str();
230 void replaceFeatures(Function
&F
, const std::string
&Features
) {
231 F
.removeFnAttr("target-features");
232 F
.removeFnAttr("target-cpu");
233 F
.addFnAttr("target-features", Features
);
236 bool stripAtomics(Module
&M
) {
237 // Detect whether any atomics will be lowered, since there is no way to tell
238 // whether the LowerAtomic pass lowers e.g. stores.
239 bool Stripped
= false;
255 LowerAtomicPass Lowerer
;
256 FunctionAnalysisManager FAM
;
263 bool stripThreadLocals(Module
&M
) {
264 bool Stripped
= false;
265 for (auto &GV
: M
.globals()) {
266 if (GV
.getThreadLocalMode() !=
267 GlobalValue::ThreadLocalMode::NotThreadLocal
) {
269 GV
.setThreadLocalMode(GlobalValue::ThreadLocalMode::NotThreadLocal
);
275 void recordFeatures(Module
&M
, const FeatureBitset
&Features
, bool Stripped
) {
276 for (const SubtargetFeatureKV
&KV
: WebAssemblyFeatureKV
) {
277 std::string MDKey
= (StringRef("wasm-feature-") + KV
.Key
).str();
278 if (KV
.Value
== WebAssembly::FeatureAtomics
&& Stripped
) {
279 // "atomics" is special: code compiled without atomics may have had its
280 // atomics lowered to nonatomic operations. In that case, atomics is
281 // disallowed to prevent unsafe linking with atomics-enabled objects.
282 assert(!Features
[WebAssembly::FeatureAtomics
] ||
283 !Features
[WebAssembly::FeatureBulkMemory
]);
284 M
.addModuleFlag(Module::ModFlagBehavior::Error
, MDKey
,
285 wasm::WASM_FEATURE_PREFIX_DISALLOWED
);
286 } else if (Features
[KV
.Value
]) {
287 // Otherwise features are marked Used or not mentioned
288 M
.addModuleFlag(Module::ModFlagBehavior::Error
, MDKey
,
289 wasm::WASM_FEATURE_PREFIX_USED
);
294 char CoalesceFeaturesAndStripAtomics::ID
= 0;
296 /// WebAssembly Code Generator Pass Configuration Options.
297 class WebAssemblyPassConfig final
: public TargetPassConfig
{
299 WebAssemblyPassConfig(WebAssemblyTargetMachine
&TM
, PassManagerBase
&PM
)
300 : TargetPassConfig(TM
, PM
) {}
302 WebAssemblyTargetMachine
&getWebAssemblyTargetMachine() const {
303 return getTM
<WebAssemblyTargetMachine
>();
306 FunctionPass
*createTargetRegisterAllocator(bool) override
;
308 void addIRPasses() override
;
309 bool addInstSelector() override
;
310 void addPostRegAlloc() override
;
311 bool addGCPasses() override
{ return false; }
312 void addPreEmitPass() override
;
315 bool addRegAssignmentFast() override
{ return false; }
318 bool addRegAssignmentOptimized() override
{ return false; }
320 } // end anonymous namespace
323 WebAssemblyTargetMachine::getTargetTransformInfo(const Function
&F
) {
324 return TargetTransformInfo(WebAssemblyTTIImpl(this, F
));
328 WebAssemblyTargetMachine::createPassConfig(PassManagerBase
&PM
) {
329 return new WebAssemblyPassConfig(*this, PM
);
332 FunctionPass
*WebAssemblyPassConfig::createTargetRegisterAllocator(bool) {
333 return nullptr; // No reg alloc
336 //===----------------------------------------------------------------------===//
337 // The following functions are called from lib/CodeGen/Passes.cpp to modify
338 // the CodeGen pass sequence.
339 //===----------------------------------------------------------------------===//
341 void WebAssemblyPassConfig::addIRPasses() {
342 // Runs LowerAtomicPass if necessary
343 addPass(new CoalesceFeaturesAndStripAtomics(&getWebAssemblyTargetMachine()));
345 // This is a no-op if atomics are not used in the module
346 addPass(createAtomicExpandPass());
348 // Add signatures to prototype-less function declarations
349 addPass(createWebAssemblyAddMissingPrototypes());
351 // Lower .llvm.global_dtors into .llvm_global_ctors with __cxa_atexit calls.
352 addPass(createWebAssemblyLowerGlobalDtors());
354 // Fix function bitcasts, as WebAssembly requires caller and callee signatures
356 addPass(createWebAssemblyFixFunctionBitcasts());
358 // Optimize "returned" function attributes.
359 if (getOptLevel() != CodeGenOpt::None
)
360 addPass(createWebAssemblyOptimizeReturned());
362 // If exception handling is not enabled and setjmp/longjmp handling is
363 // enabled, we lower invokes into calls and delete unreachable landingpad
364 // blocks. Lowering invokes when there is no EH support is done in
365 // TargetPassConfig::addPassesToHandleExceptions, but this runs after this
366 // function and SjLj handling expects all invokes to be lowered before.
367 if (!EnableEmException
&&
368 TM
->Options
.ExceptionModel
== ExceptionHandling::None
) {
369 addPass(createLowerInvokePass());
370 // The lower invoke pass may create unreachable code. Remove it in order not
371 // to process dead blocks in setjmp/longjmp handling.
372 addPass(createUnreachableBlockEliminationPass());
375 // Handle exceptions and setjmp/longjmp if enabled.
376 if (EnableEmException
|| EnableEmSjLj
)
377 addPass(createWebAssemblyLowerEmscriptenEHSjLj(EnableEmException
,
380 // Expand indirectbr instructions to switches.
381 addPass(createIndirectBrExpandPass());
383 TargetPassConfig::addIRPasses();
386 bool WebAssemblyPassConfig::addInstSelector() {
387 (void)TargetPassConfig::addInstSelector();
389 createWebAssemblyISelDag(getWebAssemblyTargetMachine(), getOptLevel()));
390 // Run the argument-move pass immediately after the ScheduleDAG scheduler
391 // so that we can fix up the ARGUMENT instructions before anything else
392 // sees them in the wrong place.
393 addPass(createWebAssemblyArgumentMove());
394 // Set the p2align operands. This information is present during ISel, however
395 // it's inconvenient to collect. Collect it now, and update the immediate
397 addPass(createWebAssemblySetP2AlignOperands());
401 void WebAssemblyPassConfig::addPostRegAlloc() {
402 // TODO: The following CodeGen passes don't currently support code containing
403 // virtual registers. Consider removing their restrictions and re-enabling
406 // These functions all require the NoVRegs property.
407 disablePass(&MachineCopyPropagationID
);
408 disablePass(&PostRAMachineSinkingID
);
409 disablePass(&PostRASchedulerID
);
410 disablePass(&FuncletLayoutID
);
411 disablePass(&StackMapLivenessID
);
412 disablePass(&LiveDebugValuesID
);
413 disablePass(&PatchableFunctionID
);
414 disablePass(&ShrinkWrapID
);
416 // This pass hurts code size for wasm because it can generate irreducible
418 disablePass(&MachineBlockPlacementID
);
420 TargetPassConfig::addPostRegAlloc();
423 void WebAssemblyPassConfig::addPreEmitPass() {
424 TargetPassConfig::addPreEmitPass();
426 // Rewrite pseudo call_indirect instructions as real instructions.
427 // This needs to run before register stackification, because we change the
428 // order of the arguments.
429 addPass(createWebAssemblyCallIndirectFixup());
431 // Eliminate multiple-entry loops.
432 addPass(createWebAssemblyFixIrreducibleControlFlow());
434 // Do various transformations for exception handling.
435 // Every CFG-changing optimizations should come before this.
436 addPass(createWebAssemblyLateEHPrepare());
438 // Now that we have a prologue and epilogue and all frame indices are
439 // rewritten, eliminate SP and FP. This allows them to be stackified,
440 // colored, and numbered with the rest of the registers.
441 addPass(createWebAssemblyReplacePhysRegs());
443 // Preparations and optimizations related to register stackification.
444 if (getOptLevel() != CodeGenOpt::None
) {
445 // LiveIntervals isn't commonly run this late. Re-establish preconditions.
446 addPass(createWebAssemblyPrepareForLiveIntervals());
448 // Depend on LiveIntervals and perform some optimizations on it.
449 addPass(createWebAssemblyOptimizeLiveIntervals());
451 // Prepare memory intrinsic calls for register stackifying.
452 addPass(createWebAssemblyMemIntrinsicResults());
454 // Mark registers as representing wasm's value stack. This is a key
455 // code-compression technique in WebAssembly. We run this pass (and
456 // MemIntrinsicResults above) very late, so that it sees as much code as
457 // possible, including code emitted by PEI and expanded by late tail
459 addPass(createWebAssemblyRegStackify());
461 // Run the register coloring pass to reduce the total number of registers.
462 // This runs after stackification so that it doesn't consider registers
463 // that become stackified.
464 addPass(createWebAssemblyRegColoring());
467 // Sort the blocks of the CFG into topological order, a prerequisite for
468 // BLOCK and LOOP markers.
469 addPass(createWebAssemblyCFGSort());
471 // Insert BLOCK and LOOP markers.
472 addPass(createWebAssemblyCFGStackify());
474 // Insert explicit local.get and local.set operators.
475 addPass(createWebAssemblyExplicitLocals());
477 // Lower br_unless into br_if.
478 addPass(createWebAssemblyLowerBrUnless());
480 // Perform the very last peephole optimizations on the code.
481 if (getOptLevel() != CodeGenOpt::None
)
482 addPass(createWebAssemblyPeephole());
484 // Create a mapping from LLVM CodeGen virtual registers to wasm registers.
485 addPass(createWebAssemblyRegNumbering());
488 yaml::MachineFunctionInfo
*
489 WebAssemblyTargetMachine::createDefaultFuncInfoYAML() const {
490 return new yaml::WebAssemblyFunctionInfo();
493 yaml::MachineFunctionInfo
*WebAssemblyTargetMachine::convertFuncInfoToYAML(
494 const MachineFunction
&MF
) const {
495 const auto *MFI
= MF
.getInfo
<WebAssemblyFunctionInfo
>();
496 return new yaml::WebAssemblyFunctionInfo(*MFI
);
499 bool WebAssemblyTargetMachine::parseMachineFunctionInfo(
500 const yaml::MachineFunctionInfo
&MFI
, PerFunctionMIParsingState
&PFS
,
501 SMDiagnostic
&Error
, SMRange
&SourceRange
) const {
502 const auto &YamlMFI
=
503 reinterpret_cast<const yaml::WebAssemblyFunctionInfo
&>(MFI
);
504 MachineFunction
&MF
= PFS
.MF
;
505 MF
.getInfo
<WebAssemblyFunctionInfo
>()->initializeBaseYamlFields(YamlMFI
);