cd46354dbd
This change is a step towards fixing one long-standing problem with LLVM's debug WASM codegen: excessive use of locals. One local for each temporary value in IR (roughly speaking). This has a lot of problems: 1) It makes it easy to hit engine limitations of 50K locals with certain code patterns and large functions. 2) It makes for larger binaries that are slower to load and slower to compile to native code. 3) It makes certain compilation strategies (spill all WASM locals to stack, for example) for debug code excessively expensive and makes debug WASM code either run very slow, or be less debuggable. 4) It slows down LLVM itself. This change addresses these partially by running a limited version of the stackification pass for unoptimized code, one that gets rid of the most 'obviously' unnecessary locals. Care needs to be taken to not impact LLVM's ability to produce high quality debug variable locations with this pass. To that end: 1) We only allow stackification when it doesn't require moving any instructions. 2) We disable stackification of any locals that are used in DEBUG_VALUEs, or as a frame base. I have verified on a moderately large example that the baseline and the diff produce the same kinds (local/global/stack) of locations, and the only differences are due to the shifting of instruction offsets, with many local.[get|set]s not being present anymore. Even with this quite conservative approach, the results are pretty good: 1) 30% reduction in raw code size, up to 10x reduction in the number of locals for select large methods (~1000 => ~100). 2) ~10% reduction in instructions retired for an "llc -O0" run on a moderately sized input.
112 lines
4.7 KiB
C++
112 lines
4.7 KiB
C++
//===-- WebAssembly.h - Top-level interface for WebAssembly ----*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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///
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/// \file
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/// This file contains the entry points for global functions defined in
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/// the LLVM WebAssembly back-end.
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIB_TARGET_WEBASSEMBLY_WEBASSEMBLY_H
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#define LLVM_LIB_TARGET_WEBASSEMBLY_WEBASSEMBLY_H
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#include "llvm/PassRegistry.h"
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#include "llvm/Support/CodeGen.h"
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namespace llvm {
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class WebAssemblyTargetMachine;
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class ModulePass;
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class FunctionPass;
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// LLVM IR passes.
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ModulePass *createWebAssemblyLowerEmscriptenEHSjLj();
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ModulePass *createWebAssemblyAddMissingPrototypes();
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ModulePass *createWebAssemblyFixFunctionBitcasts();
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FunctionPass *createWebAssemblyOptimizeReturned();
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FunctionPass *createWebAssemblyLowerRefTypesIntPtrConv();
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FunctionPass *createWebAssemblyRefTypeMem2Local();
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// ISel and immediate followup passes.
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FunctionPass *createWebAssemblyISelDag(WebAssemblyTargetMachine &TM,
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CodeGenOptLevel OptLevel);
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FunctionPass *createWebAssemblyArgumentMove();
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FunctionPass *createWebAssemblySetP2AlignOperands();
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FunctionPass *createWebAssemblyCleanCodeAfterTrap();
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// Late passes.
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FunctionPass *createWebAssemblyReplacePhysRegs();
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FunctionPass *createWebAssemblyNullifyDebugValueLists();
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FunctionPass *createWebAssemblyOptimizeLiveIntervals();
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FunctionPass *createWebAssemblyMemIntrinsicResults();
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FunctionPass *createWebAssemblyRegStackify(CodeGenOptLevel OptLevel);
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FunctionPass *createWebAssemblyRegColoring();
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FunctionPass *createWebAssemblyFixBrTableDefaults();
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FunctionPass *createWebAssemblyFixIrreducibleControlFlow();
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FunctionPass *createWebAssemblyLateEHPrepare();
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FunctionPass *createWebAssemblyCFGSort();
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FunctionPass *createWebAssemblyCFGStackify();
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FunctionPass *createWebAssemblyExplicitLocals();
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FunctionPass *createWebAssemblyLowerBrUnless();
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FunctionPass *createWebAssemblyRegNumbering();
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FunctionPass *createWebAssemblyDebugFixup();
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FunctionPass *createWebAssemblyPeephole();
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ModulePass *createWebAssemblyMCLowerPrePass();
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// PassRegistry initialization declarations.
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void initializeFixFunctionBitcastsPass(PassRegistry &);
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void initializeOptimizeReturnedPass(PassRegistry &);
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void initializeWebAssemblyRefTypeMem2LocalPass(PassRegistry &);
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void initializeWebAssemblyAddMissingPrototypesPass(PassRegistry &);
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void initializeWebAssemblyArgumentMovePass(PassRegistry &);
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void initializeWebAssemblyAsmPrinterPass(PassRegistry &);
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void initializeWebAssemblyCleanCodeAfterTrapPass(PassRegistry &);
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void initializeWebAssemblyCFGSortPass(PassRegistry &);
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void initializeWebAssemblyCFGStackifyPass(PassRegistry &);
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void initializeWebAssemblyDAGToDAGISelLegacyPass(PassRegistry &);
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void initializeWebAssemblyDebugFixupPass(PassRegistry &);
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void initializeWebAssemblyExceptionInfoPass(PassRegistry &);
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void initializeWebAssemblyExplicitLocalsPass(PassRegistry &);
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void initializeWebAssemblyFixBrTableDefaultsPass(PassRegistry &);
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void initializeWebAssemblyFixIrreducibleControlFlowPass(PassRegistry &);
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void initializeWebAssemblyLateEHPreparePass(PassRegistry &);
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void initializeWebAssemblyLowerBrUnlessPass(PassRegistry &);
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void initializeWebAssemblyLowerEmscriptenEHSjLjPass(PassRegistry &);
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void initializeWebAssemblyLowerRefTypesIntPtrConvPass(PassRegistry &);
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void initializeWebAssemblyMCLowerPrePassPass(PassRegistry &);
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void initializeWebAssemblyMemIntrinsicResultsPass(PassRegistry &);
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void initializeWebAssemblyNullifyDebugValueListsPass(PassRegistry &);
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void initializeWebAssemblyOptimizeLiveIntervalsPass(PassRegistry &);
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void initializeWebAssemblyPeepholePass(PassRegistry &);
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void initializeWebAssemblyRegColoringPass(PassRegistry &);
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void initializeWebAssemblyRegNumberingPass(PassRegistry &);
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void initializeWebAssemblyRegStackifyPass(PassRegistry &);
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void initializeWebAssemblyReplacePhysRegsPass(PassRegistry &);
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void initializeWebAssemblySetP2AlignOperandsPass(PassRegistry &);
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namespace WebAssembly {
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enum TargetIndex {
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// Followed by a local index (ULEB).
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TI_LOCAL,
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// Followed by an absolute global index (ULEB). DEPRECATED.
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TI_GLOBAL_FIXED,
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// Followed by the index from the bottom of the Wasm stack.
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TI_OPERAND_STACK,
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// Followed by a compilation unit relative global index (uint32_t)
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// that will have an associated relocation.
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TI_GLOBAL_RELOC,
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// Like TI_LOCAL, but indicates an indirect value (e.g. byval arg
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// passed by pointer).
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TI_LOCAL_INDIRECT
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};
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} // end namespace WebAssembly
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} // end namespace llvm
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#endif
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