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Revert "[llvm] Preliminary fat-lto-objects support"

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There seems to be a problem on arm buildbots. Reverting until I can
investigate.  https://lab.llvm.org/buildbot#builders/245/builds/10184

This reverts commit a67208e1c6
and dependent commit e54a3112ce.
This commit is contained in:
Paul Kirth 2023-06-23 18:43:02 +00:00
parent 62fa708ceb
commit a3800ad9d8
14 changed files with 1 additions and 300 deletions
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77
llvm/docs/FatLTO.rst
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@ -1,77 +0,0 @@
===================
FatLTO
===================
.. contents::
:local:
:depth: 2
.. toctree::
:maxdepth: 1
Introduction
============
FatLTO objects are a special type of `fat object file
<https://en.wikipedia.org/wiki/Fat_binary>`_ that contain LTO compatible IR in
addition to generated object code, instead of containing object code for
multiple target architectures. This allows users to defer the choice of whether
to use LTO or not to link-time, and has been a feature available in other
compilers, like `GCC
<https://gcc.gnu.org/onlinedocs/gccint/LTO-Overview.html>`_, for some time.
Under FatLTO the compiler can emit standard object files which contain both the
machine code in the ``.text`` section and LLVM bitcode in the ``.llvm.lto``
section.
Overview
========
Within LLVM, FatLTO is supported by choosing the ``FatLTODefaultPipeline``.
This pipeline will:
#) Clone the IR module.
#) Run the pre-link (Thin)LTO pipeline using the cloned module.
#) Embed the pre-link bitcode in a special ``.llvm.lto`` section.
#) Optimize the unmodified copy of the module using the normal compilation pipeline.
#) Emit the object file, including the new ``.llvm.lto`` section.
.. NOTE
At the time of writing, we conservatively run independent pipelines to
generate the bitcode section and the object code, which happen to be
identical to those used outside of FatLTO. This results in compiled
artifacts that are identical to those produced by the default and (Thin)LTO
pipelines. However, this is not a guarantee, and we reserve the right to
change this at any time. Explicitly, users should not rely on the produced
bitcode or object code to mach their non-LTO counterparts precisely. They
will exhibit similar performance characteristics, but may not be bit-for-bit
the same.
Internally, the ``.llvm.lto`` section is created by running the
``EmbedBitcodePass`` at the start of the ``PerModuleDefaultPipeline``. This
pass is responsible for cloning and optimizing the module with the appropriate
LTO pipeline and emitting the ``.llvm.lto`` section. Afterwards, the
``PerModuleDefaultPipeline`` runs normally and the compiler can emit the fat
object file.
Limitations
===========
Linkers
-------
Currently, using LTO with LLVM fat lto objects is supported by LLD and by the
GNU linkers via :doc:`GoldPlugin`. This may change in the future, but
extending support to other linkers isn't planned for now.
.. NOTE
For standard linking the fat object files should be usable by any
linker capable of using ELF objects, since the ``.llvm.lto`` section is
marked ``SHF_EXLUDE``.
Supported File Formats
----------------------
The current implementation only supports ELF files. At time of writing, it is
unclear if it will be useful to support other object file formats like ``COFF``
or ``Mach-O``.

6
llvm/docs/ReleaseNotes.rst
View File

@ -80,12 +80,6 @@ Changes to LLVM infrastructure
* InstructionSimplify APIs now require instructions be inserted into a
parent function.
* A new FatLTO pipeline was added to support generating object files that have
both machine code and LTO compatible bitcode. See the :doc:`FatLTO`
documentation and the original
`RFC <https://discourse.llvm.org/t/rfc-ffat-lto-objects-support/63977>`_
for more details.
Changes to building LLVM
------------------------

1
llvm/docs/UserGuides.rst
View File

@ -32,7 +32,6 @@ intermediate LLVM representation.
DebuggingJITedCode
DirectXUsage
Docker
FatLTO
ExtendingLLVM
GoldPlugin
HowToBuildOnARM

12
llvm/include/llvm/Passes/PassBuilder.h
View File

@ -234,18 +234,6 @@ public:
ModulePassManager buildPerModuleDefaultPipeline(OptimizationLevel Level,
bool LTOPreLink = false);
/// Build a fat object default optimization pipeline.
///
/// This builds a pipeline that runs the LTO/ThinLTO pre-link pipeline, and
/// emits a section containing the pre-link bitcode along side the object code
/// generated by running the PerModuleDefaultPipeline, used when compiling
/// without LTO. It clones the module and runs the LTO/non-LTO pipelines
/// separately to avoid any inconsistencies with an ad-hoc pipeline that tries
/// to approximate the PerModuleDefaultPipeline from the pre-link LTO
/// pipelines.
ModulePassManager buildFatLTODefaultPipeline(OptimizationLevel Level,
bool ThinLTO, bool EmitSummary);
/// Build a pre-link, ThinLTO-targeting default optimization pipeline to
/// a pass manager.
///

58
llvm/include/llvm/Transforms/IPO/EmbedBitcodePass.h
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@ -1,58 +0,0 @@
//===-- EmbedBitcodePass.h - Embeds bitcode into global ---------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
///
/// This file provides a pass which clones the current module and runs the
/// provided pass pipeline on the clone. The optimized module is stored into a
/// global variable in the `.llvm.lto` section. Primarily, this pass is used
/// to support the FatLTO pipeline, but could be used to generate a bitcode
/// section for any arbitrary pass pipeline without changing the current module.
///
//===----------------------------------------------------------------------===//
//
#ifndef LLVM_TRANSFORMS_IPO_EMBEDBITCODEPASS_H
#define LLVM_TRANSFORMS_IPO_EMBEDBITCODEPASS_H
#include "llvm/IR/PassManager.h"
namespace llvm {
class Module;
class ModulePass;
class Pass;
struct EmbedBitcodeOptions {
EmbedBitcodeOptions() : EmbedBitcodeOptions(false, false) {}
EmbedBitcodeOptions(bool IsThinLTO, bool EmitLTOSummary)
: IsThinLTO(IsThinLTO), EmitLTOSummary(EmitLTOSummary) {}
bool IsThinLTO;
bool EmitLTOSummary;
};
/// Pass embeds a copy of the module optimized with the provided pass pipeline
/// into a global variable.
class EmbedBitcodePass : public PassInfoMixin<EmbedBitcodePass> {
bool IsThinLTO;
bool EmitLTOSummary;
ModulePassManager MPM;
public:
EmbedBitcodePass(EmbedBitcodeOptions Opts)
: EmbedBitcodePass(Opts.IsThinLTO, Opts.EmitLTOSummary,
ModulePassManager()) {}
EmbedBitcodePass(bool IsThinLTO, bool EmitLTOSummary, ModulePassManager &&MPM)
: IsThinLTO(IsThinLTO), EmitLTOSummary(EmitLTOSummary),
MPM(std::move(MPM)) {}
PreservedAnalyses run(Module &M, ModuleAnalysisManager &);
static bool isRequired() { return true; }
};
} // end namespace llvm.
#endif

2
llvm/lib/Object/ObjectFile.cpp
View File

@ -79,7 +79,7 @@ uint32_t ObjectFile::getSymbolAlignment(DataRefImpl DRI) const { return 0; }
bool ObjectFile::isSectionBitcode(DataRefImpl Sec) const {
Expected<StringRef> NameOrErr = getSectionName(Sec);
if (NameOrErr)
return *NameOrErr == ".llvmbc" || *NameOrErr == ".llvm.lto";
return *NameOrErr == ".llvmbc";
consumeError(NameOrErr.takeError());
return false;
}

21
llvm/lib/Passes/PassBuilder.cpp
View File

@ -102,7 +102,6 @@
#include "llvm/Transforms/IPO/CrossDSOCFI.h"
#include "llvm/Transforms/IPO/DeadArgumentElimination.h"
#include "llvm/Transforms/IPO/ElimAvailExtern.h"
#include "llvm/Transforms/IPO/EmbedBitcodePass.h"
#include "llvm/Transforms/IPO/ForceFunctionAttrs.h"
#include "llvm/Transforms/IPO/FunctionAttrs.h"
#include "llvm/Transforms/IPO/FunctionImport.h"
@ -739,26 +738,6 @@ Expected<HWAddressSanitizerOptions> parseHWASanPassOptions(StringRef Params) {
return Result;
}
Expected<EmbedBitcodeOptions> parseEmbedBitcodePassOptions(StringRef Params) {
EmbedBitcodeOptions Result;
while (!Params.empty()) {
StringRef ParamName;
std::tie(ParamName, Params) = Params.split(';');
if (ParamName == "thinlto") {
Result.IsThinLTO = true;
} else if (ParamName == "emit-summary") {
Result.EmitLTOSummary = true;
} else {
return make_error<StringError>(
formatv("invalid EmbedBitcode pass parameter '{0}' ", ParamName)
.str(),
inconvertibleErrorCode());
}
}
return Result;
}
Expected<MemorySanitizerOptions> parseMSanPassOptions(StringRef Params) {
MemorySanitizerOptions Result;
while (!Params.empty()) {

12
llvm/lib/Passes/PassBuilderPipelines.cpp
View File

@ -46,7 +46,6 @@
#include "llvm/Transforms/IPO/CrossDSOCFI.h"
#include "llvm/Transforms/IPO/DeadArgumentElimination.h"
#include "llvm/Transforms/IPO/ElimAvailExtern.h"
#include "llvm/Transforms/IPO/EmbedBitcodePass.h"
#include "llvm/Transforms/IPO/ForceFunctionAttrs.h"
#include "llvm/Transforms/IPO/FunctionAttrs.h"
#include "llvm/Transforms/IPO/GlobalDCE.h"
@ -1465,18 +1464,7 @@ PassBuilder::buildPerModuleDefaultPipeline(OptimizationLevel Level,
if (LTOPreLink)
addRequiredLTOPreLinkPasses(MPM);
return MPM;
}
ModulePassManager
PassBuilder::buildFatLTODefaultPipeline(OptimizationLevel Level, bool ThinLTO,
bool EmitSummary) {
ModulePassManager MPM;
MPM.addPass(EmbedBitcodePass(ThinLTO, EmitSummary,
ThinLTO
? buildThinLTOPreLinkDefaultPipeline(Level)
: buildLTOPreLinkDefaultPipeline(Level)));
MPM.addPass(buildPerModuleDefaultPipeline(Level));
return MPM;
}

7
llvm/lib/Passes/PassRegistry.def
View File

@ -170,13 +170,6 @@ MODULE_PASS_WITH_PARAMS("ipsccp",
},
parseIPSCCPOptions,
"no-func-spec;func-spec")
MODULE_PASS_WITH_PARAMS("embed-bitcode",
"EmbedBitcodePass",
[](EmbedBitcodeOptions Opts) {
return EmbedBitcodePass(Opts);
},
parseEmbedBitcodePassOptions,
"thinlto;emit-summary")
#undef MODULE_PASS_WITH_PARAMS
#ifndef CGSCC_ANALYSIS

1
llvm/lib/Transforms/IPO/CMakeLists.txt
View File

@ -11,7 +11,6 @@ add_llvm_component_library(LLVMipo
CrossDSOCFI.cpp
DeadArgumentElimination.cpp
ElimAvailExtern.cpp
EmbedBitcodePass.cpp
ExtractGV.cpp
ForceFunctionAttrs.cpp
FunctionAttrs.cpp

50
llvm/lib/Transforms/IPO/EmbedBitcodePass.cpp
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@ -1,50 +0,0 @@
//===- EmbedBitcodePass.cpp - Pass that embeds the bitcode into a global---===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO/EmbedBitcodePass.h"
#include "llvm/Bitcode/BitcodeWriter.h"
#include "llvm/Bitcode/BitcodeWriterPass.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/PassManager.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/TargetParser/Triple.h"
#include "llvm/Transforms/IPO/ThinLTOBitcodeWriter.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
using namespace llvm;
PreservedAnalyses EmbedBitcodePass::run(Module &M, ModuleAnalysisManager &AM) {
if (M.getGlobalVariable("llvm.embedded.module", /*AllowInternal=*/true))
report_fatal_error("Can only embed the module once",
/*gen_crash_diag=*/false);
Triple T(M.getTargetTriple());
if (T.getObjectFormat() != Triple::ELF)
report_fatal_error(
"EmbedBitcode pass currently only supports ELF object format",
/*gen_crash_diag=*/false);
std::unique_ptr<Module> NewModule = CloneModule(M);
MPM.run(*NewModule, AM);
std::string Data;
raw_string_ostream OS(Data);
if (IsThinLTO)
ThinLTOBitcodeWriterPass(OS, /*ThinLinkOS=*/nullptr).run(*NewModule, AM);
else
BitcodeWriterPass(OS, /*ShouldPreserveUseListOrder=*/false, EmitLTOSummary)
.run(*NewModule, AM);
embedBufferInModule(M, MemoryBufferRef(Data, "ModuleData"), ".llvm.lto");
return PreservedAnalyses::all();
}

6
llvm/test/Transforms/EmbedBitcode/embed-multiple.ll
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@ -1,6 +0,0 @@
; RUN: not opt --mtriple x86_64-unknown-linux-gnu < %s -passes=embed-bitcode -S 2>&1 | FileCheck %s
@a = global i32 1
@llvm.embedded.module = private constant [4 x i8] c"BC\C0\DE"
; CHECK: LLVM ERROR: Can only embed the module once

5
llvm/test/Transforms/EmbedBitcode/embed-unsupported-object-format.ll
View File

@ -1,5 +0,0 @@
; RUN: not opt --mtriple powerpc64-unknown-aix < %s -passes=embed-bitcode -S 2>&1 | FileCheck %s
@a = global i32 1
; CHECK: LLVM ERROR: EmbedBitcode pass currently only supports ELF object format

43
llvm/test/Transforms/EmbedBitcode/embed.ll
View File

@ -1,43 +0,0 @@
; RUN: opt --mtriple x86_64-unknown-linux-gnu < %s -passes="embed-bitcode" -S | FileCheck %s
; RUN: opt --mtriple x86_64-unknown-linux-gnu < %s -passes="embed-bitcode<thinlto>" -S | FileCheck %s
; RUN: opt --mtriple x86_64-unknown-linux-gnu < %s -passes="embed-bitcode<emit-summary>" -S | FileCheck %s
; RUN: opt --mtriple x86_64-unknown-linux-gnu < %s -passes="embed-bitcode<thinlto;emit-summary>" -S | FileCheck %s
@a = global i32 1
; CHECK: @a = global i32 1
;; Make sure the module is in the correct section.
; CHECK: @llvm.embedded.object = private constant {{.*}}, section ".llvm.lto", align 1
;; Ensure that the metadata is in llvm.compiler.used.
; CHECK: @llvm.compiler.used = appending global [1 x ptr] [ptr @llvm.embedded.object], section "llvm.metadata"
;; Make sure the metadata correlates to the .llvm.lto section.
; CHECK: !llvm.embedded.objects = !{!1}
; CHECK: !0 = !{}
; CHECK: !{ptr @llvm.embedded.object, !".llvm.lto"}
;; Ensure that the .llvm.lto section has SHT_EXCLUDE set.
; RUN: opt --mtriple x86_64-unknown-linux-gnu < %s -passes="embed-bitcode<thinlto;emit-summary>" -S \
; RUN: | llc --mtriple x86_64-unknown-linux-gnu -filetype=obj \
; RUN: | llvm-readobj - --sections --elf-output-style=JSON --pretty-print \
; RUN: | FileCheck %s --check-prefix=EXCLUDE
; EXCLUDE: "Name": ".llvm.lto",
; EXCLUDE-NEXT: "Value": 7
; EXCLUDE-NEXT: },
; EXCLUDE-NEXT: "Type": {
; EXCLUDE-NEXT: "Name": "SHT_PROGBITS",
; EXCLUDE-NEXT: "Value": 1
; EXCLUDE-NEXT: },
; EXCLUDE-NEXT: "Flags": {
; EXCLUDE-NEXT: "Value": 2147483648,
; EXCLUDE-NEXT: "Flags": [
; EXCLUDE-NEXT: {
; EXCLUDE-NEXT: "Name": "SHF_EXCLUDE",
; EXCLUDE-NEXT: "Value": 2147483648
; EXCLUDE-NEXT: }
; EXCLUDE-NEXT: ]
; EXCLUDE-NEXT: },