mirror of
https://github.com/revng/revng
synced 2026-06-21 14:07:57 +00:00
Giacomo Vercesi
798af62b87
Re-organize the variants of `libtcg-helpers-*.bc` as such: * `libtcg-helpers-full-$ARCH.bc`: unchanged, contains all helper function with their bodies and all CSVs. * `libtcg-helpers-declarations-only-$ARCH.bc`: all helper functions have been turned to declarations. All CSVs (except a couple of special ones) have been dropped. * `libtcg-helpers-to-inline-$ARCH.bc`: only functions with the `revng_inline` section retain their body. Only CSVs that are used by these functions are present. Lift now loads only the `declarations-only` variant of helpers, as their body is not required until `inline-helpers`. In `inline-helpers` the `to-inline` variant is loaded and linked, which then allows the helpers to be inlined.
113 lines
3.7 KiB
C++
113 lines
3.7 KiB
C++
//
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// This file is distributed under the MIT License. See LICENSE.md for details.
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//
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DebugInfo.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Transforms/IPO/AlwaysInliner.h"
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#include "llvm/Transforms/IPO/GlobalDCE.h"
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#include "revng/Model/FunctionTags.h"
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#include "revng/Support/IRHelpers.h"
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#include "revng/Support/SimplePassManager.h"
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#include "PostProcessingHelpers.h"
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using namespace llvm;
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class SlimDownHelpersModule : public llvm::ModulePass {
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public:
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static char ID;
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public:
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SlimDownHelpersModule() : llvm::ModulePass(ID) {}
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bool runOnModule(llvm::Module &M) override {
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LLVMContext &Context = M.getContext();
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for (Function &F : M) {
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if (F.isDeclaration() or F.isIntrinsic())
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continue;
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// Remove the body of all the functions *not* tagged with `revng_inline`
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if (F.getSection() != InlineHelpersSection) {
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deleteOnlyBody(F);
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} else {
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llvm::stripDebugInfo(F);
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F.removeFnAttr(Attribute::NoInline);
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F.addFnAttr(Attribute::AlwaysInline);
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F.setDSOLocal(false);
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F.setVisibility(GlobalValue::DefaultVisibility);
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}
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}
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// Now that all of the non-`revng_inline` functions have gone, we want to
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// reduce the number of global variables with some help from GlobalDCE.
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// We have three type of variables:
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// * Special variables (`arch_cpu_type_beacon`, `cpu_loop_exiting`) which
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// should not be touched
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// * CSVs we want to keep only the ones used by the `revng_inline`
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// functions, so we set their linkage temporarily to internal, run
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// `globaldce` and then restore them to their original linkage
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// * The rest (QEMU globals) do not need their initializer, so it's removed
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// and their linkage is set to external. `globaldce` will also remove
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// them if they are unused
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StringMap<GlobalValue::LinkageTypes> GlobalLinkageBackup;
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for (GlobalVariable &GV : M.globals()) {
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GV.eraseMetadata(LLVMContext::MD_dbg);
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if (GV.isDeclaration() or isSpecialGV(GV))
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continue;
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if (FunctionTags::CSV.isTagOf(&GV)) {
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// Save linkage to be restored after we run globaldce
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GlobalLinkageBackup[GV.getName()] = GV.getLinkage();
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GV.setLinkage(GlobalValue::InternalLinkage);
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} else {
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// Blank out initializers for any non-CSV GlobalVariable
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GV.setInitializer(nullptr);
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GV.setLinkage(GlobalValue::ExternalLinkage);
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}
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}
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// Run always-inline and globaldce.
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// It's important to run `always-inline` now so that when the helper
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// functions are inlined into the main module it can be done in a single
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// pass and not in a fixed-point fashion.
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SimplePassManager PM;
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PM.addPass(llvm::AlwaysInlinerPass());
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PM.addPass(llvm::GlobalDCEPass());
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PM.run(M);
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// Restore the linkage to CSVs after running globaldce
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for (GlobalVariable &GV : M.globals()) {
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if (GlobalLinkageBackup.count(GV.getName()) != 0)
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GV.setLinkage(GlobalLinkageBackup[GV.getName()]);
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}
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// Helper functions, down the pipeline, will be given the `NoInline`
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// attribute, to avoid the module failing verification remove the
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// `AlwaysInline` attribute.
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for (llvm::Function &F : M) {
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if (F.getSection() == InlineHelpersSection)
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F.removeFnAttr(Attribute::AlwaysInline);
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}
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// Tag all globals
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tagQEMUGlobalsAndFunctions(M);
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return true;
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}
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};
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char SlimDownHelpersModule::ID = 0;
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using Register = RegisterPass<SlimDownHelpersModule>;
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static Register X("slim-down-helpers-module",
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"Purge non-inline helper functions but keep their "
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"declarations alive in a array of pointers.",
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true,
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true);
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