c9f573463e
The collection of library function names in TargetLibraryInfo faces similar challenges as RuntimeLibCalls in the IR component. The number of function names is large, there are numerous customizations based on the triple (including alternate names), and there is a lot of replicated data in the signature table. The ultimate goal would be to capture all lbrary function related information in a .td file. This PR brings the current .def file to TableGen, almost as a 1:1 replacement. However, there are some improvements which are not possible in the current implementation: - the function names are now stored as a long string together with an offset table. - the table of signatures is now deduplicated, using an offset table for access. The size of the object file decreases about 34kB with these changes. The hash table of all function names is still constructed dynamically. A static table like for RuntimeLibCalls is the next logical step. The main motivation for this change is that I have to add a large number of custom names for z/OS (like in RuntimeLibCalls.td), and the current infrastructur does not support this very well.
134 lines
4.5 KiB
C++
134 lines
4.5 KiB
C++
//==-LTOInternalize.cpp - LLVM Link Time Optimizer Internalization Utility -==//
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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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// This file defines a helper to run the internalization part of LTO.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/LTO/legacy/UpdateCompilerUsed.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/CodeGen/TargetLowering.h"
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#include "llvm/CodeGen/TargetSubtargetInfo.h"
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#include "llvm/IR/Mangler.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Transforms/Utils/ModuleUtils.h"
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using namespace llvm;
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namespace {
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// Helper class that collects AsmUsed and user supplied libcalls.
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class PreserveLibCallsAndAsmUsed {
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public:
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PreserveLibCallsAndAsmUsed(const StringSet<> &AsmUndefinedRefs,
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const TargetMachine &TM,
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std::vector<GlobalValue *> &LLVMUsed)
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: AsmUndefinedRefs(AsmUndefinedRefs), TM(TM), LLVMUsed(LLVMUsed) {}
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void findInModule(Module &TheModule) {
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initializeLibCalls(TheModule);
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for (Function &F : TheModule)
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findLibCallsAndAsm(F);
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for (GlobalVariable &GV : TheModule.globals())
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findLibCallsAndAsm(GV);
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for (GlobalAlias &GA : TheModule.aliases())
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findLibCallsAndAsm(GA);
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}
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private:
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// Inputs
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const StringSet<> &AsmUndefinedRefs;
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const TargetMachine &TM;
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// Temps
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llvm::Mangler Mangler;
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StringSet<> Libcalls;
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// Output
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std::vector<GlobalValue *> &LLVMUsed;
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// Collect names of runtime library functions. User-defined functions with the
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// same names are added to llvm.compiler.used to prevent them from being
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// deleted by optimizations.
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void initializeLibCalls(const Module &TheModule) {
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TargetLibraryInfoImpl TLII(TM.getTargetTriple());
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TargetLibraryInfo TLI(TLII);
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// TargetLibraryInfo has info on C runtime library calls on the current
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// target.
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for (unsigned I = LibFunc::Begin_LibFunc, E = LibFunc::End_LibFunc; I != E;
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++I) {
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LibFunc F = static_cast<LibFunc>(I);
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if (TLI.has(F))
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Libcalls.insert(TLI.getName(F));
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}
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SmallPtrSet<const TargetLowering *, 1> TLSet;
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for (const Function &F : TheModule) {
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const TargetLowering *Lowering =
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TM.getSubtargetImpl(F)->getTargetLowering();
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if (Lowering && TLSet.insert(Lowering).second)
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// TargetLowering has info on library calls that CodeGen expects to be
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// available, both from the C runtime and compiler-rt.
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for (unsigned I = 0, E = static_cast<unsigned>(RTLIB::UNKNOWN_LIBCALL);
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I != E; ++I)
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if (const char *Name =
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Lowering->getLibcallName(static_cast<RTLIB::Libcall>(I)))
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Libcalls.insert(Name);
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}
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}
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void findLibCallsAndAsm(GlobalValue &GV) {
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// There are no restrictions to apply to declarations.
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if (GV.isDeclaration())
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return;
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// There is nothing more restrictive than private linkage.
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if (GV.hasPrivateLinkage())
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return;
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// Conservatively append user-supplied runtime library functions (supplied
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// either directly, or via a function alias) to llvm.compiler.used. These
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// could be internalized and deleted by optimizations like -globalopt,
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// causing problems when later optimizations add new library calls (e.g.,
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// llvm.memset => memset and printf => puts).
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// Leave it to the linker to remove any dead code (e.g. with -dead_strip).
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GlobalValue *FuncAliasee = nullptr;
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if (isa<GlobalAlias>(GV)) {
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auto *A = cast<GlobalAlias>(&GV);
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FuncAliasee = dyn_cast<Function>(A->getAliasee());
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}
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if ((isa<Function>(GV) || FuncAliasee) && Libcalls.count(GV.getName())) {
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LLVMUsed.push_back(&GV);
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return;
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}
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SmallString<64> Buffer;
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TM.getNameWithPrefix(Buffer, &GV, Mangler);
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if (AsmUndefinedRefs.count(Buffer))
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LLVMUsed.push_back(&GV);
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}
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};
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} // namespace anonymous
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void llvm::updateCompilerUsed(Module &TheModule, const TargetMachine &TM,
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const StringSet<> &AsmUndefinedRefs) {
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std::vector<GlobalValue *> UsedValues;
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PreserveLibCallsAndAsmUsed(AsmUndefinedRefs, TM, UsedValues)
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.findInModule(TheModule);
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if (UsedValues.empty())
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return;
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appendToCompilerUsed(TheModule, UsedValues);
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}
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