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AsmParser/03-May-2024-590466

Disassembler/03-May-2024-215168

InstPrinter/03-May-2024-351266

MCTargetDesc/03-May-2024-1,298905

TargetInfo/03-May-2024-6946

CMakeLists.txtD03-May-20242.1 KiB6559

LLVMBuild.txtD03-May-20241.1 KiB3531

README.txtD03-May-20248.3 KiB197137

WebAssembly.hD03-May-20243.5 KiB8657

WebAssembly.tdD03-May-20243.6 KiB9776

WebAssemblyAddMissingPrototypes.cppD03-May-20244.8 KiB14596

WebAssemblyArgumentMove.cppD03-May-20243.3 KiB9955

WebAssemblyAsmPrinter.cppD03-May-202410.6 KiB290217

WebAssemblyAsmPrinter.hD03-May-20242.7 KiB7748

WebAssemblyCFGSort.cppD03-May-202410.2 KiB281193

WebAssemblyCFGStackify.cppD03-May-202414.7 KiB381266

WebAssemblyCallIndirectFixup.cppD03-May-20244.8 KiB13785

WebAssemblyExceptionInfo.cppD03-May-20246.3 KiB198139

WebAssemblyExceptionInfo.hD03-May-20246.2 KiB171111

WebAssemblyExplicitLocals.cppD03-May-202414.3 KiB393288

WebAssemblyFastISel.cppD03-May-202440 KiB1,3601,142

WebAssemblyFixFunctionBitcasts.cppD03-May-20248.1 KiB238157

WebAssemblyFixIrreducibleControlFlow.cppD03-May-202410.6 KiB300204

WebAssemblyFrameLowering.cppD03-May-20249.5 KiB240161

WebAssemblyFrameLowering.hD03-May-20242.1 KiB5828

WebAssemblyISD.defD03-May-2024786 2622

WebAssemblyISelDAGToDAG.cppD03-May-20243.6 KiB11360

WebAssemblyISelLowering.cppD03-May-202435.8 KiB905671

WebAssemblyISelLowering.hD03-May-20244.4 KiB10773

WebAssemblyInstrAtomics.tdD03-May-202433.3 KiB658565

WebAssemblyInstrCall.tdD03-May-20248.1 KiB165148

WebAssemblyInstrControl.tdD03-May-20247.8 KiB195171

WebAssemblyInstrConv.tdD03-May-202412.7 KiB223208

WebAssemblyInstrExceptRef.tdD03-May-20241.3 KiB3227

WebAssemblyInstrFloat.tdD03-May-20244.4 KiB10486

WebAssemblyInstrFormats.tdD03-May-20248.4 KiB168160

WebAssemblyInstrInfo.cppD03-May-20246.8 KiB204154

WebAssemblyInstrInfo.hD03-May-20242.3 KiB6436

WebAssemblyInstrInfo.tdD03-May-202412.1 KiB288245

WebAssemblyInstrInteger.tdD03-May-20244.3 KiB10087

WebAssemblyInstrMemory.tdD03-May-202423.1 KiB500429

WebAssemblyInstrSIMD.tdD03-May-2024663 2018

WebAssemblyLateEHPrepare.cppD03-May-202414 KiB384257

WebAssemblyLowerBrUnless.cppD03-May-20245.5 KiB139100

WebAssemblyLowerEmscriptenEHSjLj.cppD03-May-202444.7 KiB1,159641

WebAssemblyLowerGlobalDtors.cppD03-May-20247 KiB195134

WebAssemblyMCInstLower.cppD03-May-20248.5 KiB233176

WebAssemblyMCInstLower.hD03-May-20241.5 KiB4724

WebAssemblyMachineFunctionInfo.cppD03-May-20242.2 KiB6337

WebAssemblyMachineFunctionInfo.hD03-May-20244.3 KiB12874

WebAssemblyOptimizeLiveIntervals.cppD03-May-20243.9 KiB10965

WebAssemblyOptimizeReturned.cppD03-May-20242.4 KiB8153

WebAssemblyPeephole.cppD03-May-20247.5 KiB209171

WebAssemblyPrepareForLiveIntervals.cppD03-May-20244.3 KiB12873

WebAssemblyRegColoring.cppD03-May-20246.3 KiB178125

WebAssemblyRegNumbering.cppD03-May-20243.8 KiB11274

WebAssemblyRegStackify.cppD03-May-202433.7 KiB890601

WebAssemblyRegisterInfo.cppD03-May-20245.7 KiB149108

WebAssemblyRegisterInfo.hD03-May-20241.7 KiB5526

WebAssemblyRegisterInfo.tdD03-May-20242.8 KiB6956

WebAssemblyReplacePhysRegs.cppD03-May-20243.5 KiB10466

WebAssemblyRuntimeLibcallSignatures.cppD03-May-202431.7 KiB845769

WebAssemblyRuntimeLibcallSignatures.hD03-May-20241.3 KiB3816

WebAssemblySelectionDAGInfo.cppD03-May-2024674 214

WebAssemblySelectionDAGInfo.hD03-May-2024882 3110

WebAssemblySetP2AlignOperands.cppD03-May-20246.6 KiB180150

WebAssemblyStoreResults.cppD03-May-20247.1 KiB206137

WebAssemblySubtarget.cppD03-May-20242 KiB5729

WebAssemblySubtarget.hD03-May-20243.1 KiB9455

WebAssemblyTargetMachine.cppD03-May-202413 KiB343193

WebAssemblyTargetMachine.hD03-May-20241.7 KiB5426

WebAssemblyTargetObjectFile.cppD03-May-2024858 268

WebAssemblyTargetObjectFile.hD03-May-2024931 3110

WebAssemblyTargetTransformInfo.cppD03-May-20242.7 KiB8450

WebAssemblyTargetTransformInfo.hD03-May-20242.4 KiB7432

WebAssemblyUtilities.cppD03-May-20246.6 KiB243210

WebAssemblyUtilities.hD03-May-20242.4 KiB7335

known_gcc_test_failures.txtD03-May-20242 KiB120112

README.txt

1//===-- README.txt - Notes for WebAssembly code gen -----------------------===//
2
3This WebAssembly backend is presently under development.
4
5The most notable feature which is not yet stable is the ".o" file format.
6".o" file support is needed for many common ways of using LLVM, such as
7using it through "clang -c", so this backend is not yet considered widely
8usable. However, this backend is usable within some language toolchain
9packages:
10
11Emscripten provides a C/C++ compilation environment that includes standard
12libraries, tools, and packaging for producing WebAssembly applications that
13can run in browsers and other environments. For more information, see the
14Emscripten documentation in general, and this page in particular:
15
16  * https://github.com/kripken/emscripten/wiki/New-WebAssembly-Backend
17
18Rust provides WebAssembly support integrated into Cargo. There are two
19main options:
20 - wasm32-unknown-unknown, which provides a relatively minimal environment
21   that has an emphasis on being "native"
22 - wasm32-unknown-emscripten, which uses Emscripten internally and
23   provides standard C/C++ libraries, filesystem emulation, GL and SDL
24   bindings
25For more information, see:
26  * https://www.hellorust.com/
27
28
29This backend does not yet support debug info. Full DWARF support needs a
30design for how DWARF should be represented in WebAssembly. Sourcemap support
31has an existing design and some corresponding browser implementations, so it
32just needs implementing in LLVM.
33
34Work-in-progress documentation for the ".o" file format is here:
35
36  * https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
37
38A corresponding linker implementation is also under development:
39
40  * https://lld.llvm.org/WebAssembly.html
41
42For more information on WebAssembly itself, see the home page:
43  * https://webassembly.github.io/
44
45The following documents contain some information on the semantics and binary
46encoding of WebAssembly itself:
47  * https://github.com/WebAssembly/design/blob/master/Semantics.md
48  * https://github.com/WebAssembly/design/blob/master/BinaryEncoding.md
49
50The backend is built, tested and archived on the following waterfall:
51  https://wasm-stat.us
52
53The backend's bringup is done in part by using the GCC torture test suite, since
54it doesn't require C library support. Current known failures are in
55known_gcc_test_failures.txt, all other tests should pass. The waterfall will
56turn red if not. Once most of these pass, further testing will use LLVM's own
57test suite. The tests can be run locally using:
58  https://github.com/WebAssembly/waterfall/blob/master/src/compile_torture_tests.py
59
60Some notes on ways that the generated code could be improved follow:
61
62//===---------------------------------------------------------------------===//
63
64Br, br_if, and br_table instructions can support having a value on the value
65stack across the jump (sometimes). We should (a) model this, and (b) extend
66the stackifier to utilize it.
67
68//===---------------------------------------------------------------------===//
69
70The min/max instructions aren't exactly a<b?a:b because of NaN and negative zero
71behavior. The ARM target has the same kind of min/max instructions and has
72implemented optimizations for them; we should do similar optimizations for
73WebAssembly.
74
75//===---------------------------------------------------------------------===//
76
77AArch64 runs SeparateConstOffsetFromGEPPass, followed by EarlyCSE and LICM.
78Would these be useful to run for WebAssembly too? Also, it has an option to
79run SimplifyCFG after running the AtomicExpand pass. Would this be useful for
80us too?
81
82//===---------------------------------------------------------------------===//
83
84Register stackification uses the VALUE_STACK physical register to impose
85ordering dependencies on instructions with stack operands. This is pessimistic;
86we should consider alternate ways to model stack dependencies.
87
88//===---------------------------------------------------------------------===//
89
90Lots of things could be done in WebAssemblyTargetTransformInfo.cpp. Similarly,
91there are numerous optimization-related hooks that can be overridden in
92WebAssemblyTargetLowering.
93
94//===---------------------------------------------------------------------===//
95
96Instead of the OptimizeReturned pass, which should consider preserving the
97"returned" attribute through to MachineInstrs and extending the StoreResults
98pass to do this optimization on calls too. That would also let the
99WebAssemblyPeephole pass clean up dead defs for such calls, as it does for
100stores.
101
102//===---------------------------------------------------------------------===//
103
104Consider implementing optimizeSelect, optimizeCompareInstr, optimizeCondBranch,
105optimizeLoadInstr, and/or getMachineCombinerPatterns.
106
107//===---------------------------------------------------------------------===//
108
109Find a clean way to fix the problem which leads to the Shrink Wrapping pass
110being run after the WebAssembly PEI pass.
111
112//===---------------------------------------------------------------------===//
113
114When setting multiple local variables to the same constant, we currently get
115code like this:
116
117    i32.const   $4=, 0
118    i32.const   $3=, 0
119
120It could be done with a smaller encoding like this:
121
122    i32.const   $push5=, 0
123    tee_local   $push6=, $4=, $pop5
124    copy_local  $3=, $pop6
125
126//===---------------------------------------------------------------------===//
127
128WebAssembly registers are implicitly initialized to zero. Explicit zeroing is
129therefore often redundant and could be optimized away.
130
131//===---------------------------------------------------------------------===//
132
133Small indices may use smaller encodings than large indices.
134WebAssemblyRegColoring and/or WebAssemblyRegRenumbering should sort registers
135according to their usage frequency to maximize the usage of smaller encodings.
136
137//===---------------------------------------------------------------------===//
138
139Many cases of irreducible control flow could be transformed more optimally
140than via the transform in WebAssemblyFixIrreducibleControlFlow.cpp.
141
142It may also be worthwhile to do transforms before register coloring,
143particularly when duplicating code, to allow register coloring to be aware of
144the duplication.
145
146//===---------------------------------------------------------------------===//
147
148WebAssemblyRegStackify could use AliasAnalysis to reorder loads and stores more
149aggressively.
150
151//===---------------------------------------------------------------------===//
152
153WebAssemblyRegStackify is currently a greedy algorithm. This means that, for
154example, a binary operator will stackify with its user before its operands.
155However, if moving the binary operator to its user moves it to a place where
156its operands can't be moved to, it would be better to leave it in place, or
157perhaps move it up, so that it can stackify its operands. A binary operator
158has two operands and one result, so in such cases there could be a net win by
159preferring the operands.
160
161//===---------------------------------------------------------------------===//
162
163Instruction ordering has a significant influence on register stackification and
164coloring. Consider experimenting with the MachineScheduler (enable via
165enableMachineScheduler) and determine if it can be configured to schedule
166instructions advantageously for this purpose.
167
168//===---------------------------------------------------------------------===//
169
170WebAssemblyRegStackify currently assumes that the stack must be empty after
171an instruction with no return values, however wasm doesn't actually require
172this. WebAssemblyRegStackify could be extended, or possibly rewritten, to take
173full advantage of what WebAssembly permits.
174
175//===---------------------------------------------------------------------===//
176
177Add support for mergeable sections in the Wasm writer, such as for strings and
178floating-point constants.
179
180//===---------------------------------------------------------------------===//
181
182The function @dynamic_alloca_redzone in test/CodeGen/WebAssembly/userstack.ll
183ends up with a tee_local in its prolog which has an unused result, requiring
184an extra drop:
185
186    get_global  $push8=, 0
187    tee_local   $push9=, 1, $pop8
188    drop        $pop9
189    [...]
190
191The prologue code initially thinks it needs an FP register, but later it
192turns out to be unneeded, so one could either approach this by being more
193clever about not inserting code for an FP in the first place, or optimizing
194away the copy later.
195
196//===---------------------------------------------------------------------===//
197