================ @@ -0,0 +1,1056 @@ +//===-- ExpandVariadicsPass.cpp --------------------------------*- 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 +// +//===----------------------------------------------------------------------===// +// +// This is an optimization pass for variadic functions. If called from codegen, +// it can serve as the implementation of variadic functions for a given target. +// +// The strategy is to turn the ... part of a varidic function into a va_list +// and fix up the call sites. This is completely effective if the calling +// convention can declare that to be the right thing, e.g. on GPUs or where +// the application is wholly statically linked. In the usual case, it will +// replace known calls to known variadic functions with calls that are amenable +// to inlining and other optimisations. +// +// The target-dependent parts are in class VariadicABIInfo. Enabling a new +// target means adding a case to VariadicABIInfo::create() along with tests. +// This will be especially simple if the va_list representation is a char*. +// +// The majority of the plumbing is splitting the variadic function into a +// single basic block that packs the variadic arguments into a va_list and +// a second function that does the work of the original. The target specific +// part is packing arguments into a contiguous buffer that the clang expansion +// of va_arg will do the right thing with. +// +// The aggregate effect is to unblock other transforms, most critically the +// general purpose inliner. Known calls to variadic functions become zero cost. +// +// Consistency with clang is primarily tested by emitting va_arg using clang +// then expanding the variadic functions using this pass, followed by trying +// to constant fold the functions to no-ops. +// +// Target specific behaviour is tested in IR - mainly checking that values are +// put into positions in call frames that make sense for that particular target. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/IPO/ExpandVariadics.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/CodeGen/Passes.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/PassManager.h" +#include "llvm/InitializePasses.h" +#include "llvm/Pass.h" +#include "llvm/Passes/OptimizationLevel.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/TargetParser/Triple.h" + +#include <cstdio> + +#define DEBUG_TYPE "expand-variadics" + +using namespace llvm; + +cl::opt<ExpandVariadicsMode> ExpandVariadicsModeOption( + DEBUG_TYPE "-override", cl::desc("Override the behaviour of " DEBUG_TYPE), + cl::init(ExpandVariadicsMode::unspecified), + cl::values(clEnumValN(ExpandVariadicsMode::unspecified, "unspecified", + "Use the implementation defaults"), + clEnumValN(ExpandVariadicsMode::disable, "disable", + "Disable the pass entirely"), + clEnumValN(ExpandVariadicsMode::optimize, "optimize", + "Optimise without changing ABI"), + clEnumValN(ExpandVariadicsMode::lowering, "lowering", + "Change variadic calling convention"))); + +namespace { + +// Module implements getFunction() which returns nullptr on missing declaration +// and getOrInsertFunction which creates one when absent. Intrinsics.h +// implements getDeclaration which creates one when missing. This should be +// changed to be consistent with Module()'s naming. Implementing as a local +// function here in the meantime to decouple from that process. +Function *getPreexistingDeclaration(Module *M, Intrinsic::ID id, + ArrayRef<Type *> Tys = std::nullopt) { + auto *FT = Intrinsic::getType(M->getContext(), id, Tys); + return M->getFunction(Tys.empty() ? Intrinsic::getName(id) + : Intrinsic::getName(id, Tys, M, FT)); +} + +// Lots of targets use a void* pointed at a buffer for va_list. +// Some use more complicated iterator constructs. Type erase that +// so the rest of the pass can operation on either. +// Virtual functions where different targets want different behaviour, +// normal where all implemented targets presently have the same. +struct VAListInterface { + virtual ~VAListInterface() {} + + // Whether a valist instance is passed by value or by address + // I.e. does it need to be alloca'ed and stored into, or can + // it be passed directly in a SSA register + virtual bool passedInSSARegister() = 0; + + // The type of a va_list iterator object + virtual Type *vaListType(LLVMContext &Ctx) = 0; + + // The type of a va_list as a function argument as lowered by C + virtual Type *vaListParameterType(Module &M) = 0; + + // Initialise an allocated va_list object to point to an already + // initialised contiguous memory region. + // Return the value to pass as the va_list argument + virtual Value *initializeVAList(LLVMContext &Ctx, IRBuilder<> &Builder, + AllocaInst *, Value * /*buffer*/) = 0; + + // Simple lowering suffices for va_end, va_copy for current targets + bool vaEndIsNop() { return true; } + bool vaCopyIsMemcpy() { return true; } +}; + +// The majority case - a void* into an alloca +struct VoidPtr final : public VAListInterface { + bool passedInSSARegister() override { return true; } + + Type *vaListType(LLVMContext &Ctx) override { + return PointerType::getUnqual(Ctx); + } + + Type *vaListParameterType(Module &M) override { + return PointerType::getUnqual(M.getContext()); + } + + Value *initializeVAList(LLVMContext &Ctx, IRBuilder<> &Builder, + AllocaInst * /*va_list*/, Value *buffer) override { + return buffer; + } +}; + +struct VoidPtrAllocaAddrspace final : public VAListInterface { + + bool passedInSSARegister() override { return true; } + + Type *vaListType(LLVMContext &Ctx) override { + return PointerType::getUnqual(Ctx); + } + + Type *vaListParameterType(Module &M) override { + const DataLayout &DL = M.getDataLayout(); + return DL.getAllocaPtrType(M.getContext()); + } + + Value *initializeVAList(LLVMContext &Ctx, IRBuilder<> &Builder, + AllocaInst * /*va_list*/, Value *buffer) override { + return buffer; + } +}; + +// SystemV as used by X64 Linux and others +struct SystemV final : public VAListInterface { + bool passedInSSARegister() override { return false; } + + Type *vaListType(LLVMContext &Ctx) override { + auto I32 = Type::getInt32Ty(Ctx); + auto Ptr = PointerType::getUnqual(Ctx); + return ArrayType::get(StructType::get(Ctx, {I32, I32, Ptr, Ptr}), 1); + } + + Type *vaListParameterType(Module &M) override { + return PointerType::getUnqual(M.getContext()); + } + + Value *initializeVAList(LLVMContext &Ctx, IRBuilder<> &Builder, + AllocaInst *VaList, Value *VoidBuffer) override { + assert(VaList->getAllocatedType() == vaListType(Ctx)); + + Type *VaListTy = vaListType(Ctx); + + Type *I32 = Type::getInt32Ty(Ctx); + Type *I64 = Type::getInt64Ty(Ctx); + + Value *Idxs[3] = { + ConstantInt::get(I64, 0), + ConstantInt::get(I32, 0), + nullptr, + }; + + Idxs[2] = ConstantInt::get(I32, 0); + Builder.CreateStore( + ConstantInt::get(I32, 48), + Builder.CreateInBoundsGEP(VaListTy, VaList, Idxs, "gp_offset")); + + Idxs[2] = ConstantInt::get(I32, 1); + Builder.CreateStore( + ConstantInt::get(I32, 6 * 8 + 8 * 16), + Builder.CreateInBoundsGEP(VaListTy, VaList, Idxs, "fp_offset")); + + Idxs[2] = ConstantInt::get(I32, 2); + Builder.CreateStore( + VoidBuffer, + Builder.CreateInBoundsGEP(VaListTy, VaList, Idxs, "overfow_arg_area")); + + Idxs[2] = ConstantInt::get(I32, 3); + Builder.CreateStore( + ConstantPointerNull::get(PointerType::getUnqual(Ctx)), + Builder.CreateInBoundsGEP(VaListTy, VaList, Idxs, "reg_save_area")); + + return VaList; + } +}; + +class VariadicABIInfo { + + VariadicABIInfo(uint32_t MinAlign, uint32_t MaxAlign, + std::unique_ptr<VAListInterface> VAList) + : MinAlign(MinAlign), MaxAlign(MaxAlign), VAList(std::move(VAList)) {} + + template <typename T> + static VariadicABIInfo create(uint32_t MinAlign, uint32_t MaxAlign) { + return {MinAlign, MaxAlign, std::make_unique<T>()}; + } + +public: + const uint32_t MinAlign; + const uint32_t MaxAlign; + std::unique_ptr<VAListInterface> VAList; + + VariadicABIInfo() : VariadicABIInfo(0, 0, nullptr) {} + explicit operator bool() const { return static_cast<bool>(VAList); } + + VariadicABIInfo(VariadicABIInfo &&Self) + : MinAlign(Self.MinAlign), MaxAlign(Self.MaxAlign), + VAList(Self.VAList.release()) {} + + VariadicABIInfo &operator=(VariadicABIInfo &&Other) { + this->~VariadicABIInfo(); + new (this) VariadicABIInfo(std::move(Other)); + return *this; + } + + static VariadicABIInfo create(llvm::Triple const &Triple) { + const bool IsLinuxABI = Triple.isOSLinux() || Triple.isOSCygMing(); + + switch (Triple.getArch()) { + + case Triple::r600: + case Triple::amdgcn: { + return create<VoidPtrAllocaAddrspace>(1, 0); + } + + case Triple::nvptx: + case Triple::nvptx64: { + return create<VoidPtr>(4, 0); + } + + case Triple::x86: { + // These seem to all fall out the same, despite getTypeStackAlign + // implying otherwise. + + if (Triple.isOSDarwin()) { + // X86_32ABIInfo::getTypeStackAlignInBytes is misleading for this. + // The slotSize(4) implies a minimum alignment + // The AllowHigherAlign = true means there is no maximum alignment. + + return create<VoidPtr>(4, 0); + } + if (Triple.getOS() == llvm::Triple::Win32) { + return create<VoidPtr>(4, 0); + } + + if (IsLinuxABI) { + return create<VoidPtr>(4, 0); + } + + break; + } + + case Triple::x86_64: { + if (Triple.isWindowsMSVCEnvironment() || Triple.isOSWindows()) { + // x64 msvc emit vaarg passes > 8 byte values by pointer + // however the variadic call instruction created does not, e.g. + // a <4 x f32> will be passed as itself, not as a pointer or byval. + // Postponing resolution of that for now. + // Expected min/max align of 8. + return {}; + } + + // SystemV X64 documented behaviour: + // Slots are at least eight byte aligned and at most 16 byte aligned. + // If the type needs more than sixteen byte alignment, it still only gets + // that much alignment on the stack. + // X64 behaviour in clang: + // Slots are at least eight byte aligned and at most naturally aligned + // This matches clang, not the ABI docs. + + if (Triple.isOSDarwin()) { + return create<SystemV>(8, 8); + } + + if (IsLinuxABI) { + return create<SystemV>(8, 8); + } + + break; + } + + default: + break; + } + + return {}; + } +}; + +class ExpandVariadics : public ModulePass { + + // The pass construction sets the default (optimize when called from middle + // end, lowering when called from the backend). The command line variable + // overrides that. This is useful for testing and debugging. It also allows + // building an applications with variadic functions wholly removed if one + // has sufficient control over the dependencies, e.g. a statically linked + // clang that has no variadic function calls remaining in the binary. + static ExpandVariadicsMode + withCommandLineOverride(ExpandVariadicsMode LLVMRequested) { + ExpandVariadicsMode UserRequested = ExpandVariadicsModeOption; + return (UserRequested == ExpandVariadicsMode::unspecified) ? LLVMRequested + : UserRequested; + } + +public: + static char ID; + const ExpandVariadicsMode Mode; + VariadicABIInfo ABI; + + ExpandVariadics(ExpandVariadicsMode Mode) + : ModulePass(ID), Mode(withCommandLineOverride(Mode)) {} + StringRef getPassName() const override { return "Expand variadic functions"; } + + // Rewrite a variadic call site + bool expandCall(Module &M, IRBuilder<> &Builder, CallBase *CB, FunctionType *, + Function *NF); + + // Given a variadic function, return a function taking a va_list that can be + // called instead of the original. Mutates F. + Function *deriveInlinableVariadicFunctionPair(Module &M, IRBuilder<> &Builder, + Function &F); + + bool runOnFunction(Module &M, IRBuilder<> &Builder, Function *F); + + // Entry point + bool runOnModule(Module &M) override; + + bool rewriteABI() { return Mode == ExpandVariadicsMode::lowering; } + + void memcpyVAListPointers(const DataLayout &DL, IRBuilder<> &Builder, + Value *Dst, Value *Src) { + auto &Ctx = Builder.getContext(); + Type *VaListTy = ABI.VAList->vaListType(Ctx); + uint64_t Size = DL.getTypeAllocSize(VaListTy).getFixedValue(); + // todo: on amdgcn this should be in terms of addrspace 5 + Builder.CreateMemCpyInline(Dst, {}, Src, {}, + ConstantInt::get(Type::getInt32Ty(Ctx), Size)); + } + + bool expandVAIntrinsicCall(IRBuilder<> &Builder, const DataLayout &DL, + VAStartInst *Inst); + + bool expandVAIntrinsicCall(IRBuilder<> &, const DataLayout &, + VAEndInst *Inst); + + bool expandVAIntrinsicCall(IRBuilder<> &Builder, const DataLayout &DL, + VACopyInst *Inst); + + template <Intrinsic::ID ID, typename InstructionType> + bool expandIntrinsicUsers(Module &M, IRBuilder<> &Builder, + PointerType *ArgType) { + bool Changed = false; + const DataLayout &DL = M.getDataLayout(); + if (Function *Intrinsic = getPreexistingDeclaration(&M, ID, {ArgType})) { + for (User *U : Intrinsic->users()) { + if (auto *I = dyn_cast<InstructionType>(U)) { + Changed |= expandVAIntrinsicCall(Builder, DL, I); + } + } + if (Intrinsic->use_empty()) + Intrinsic->eraseFromParent(); + } + return Changed; + } + + FunctionType *inlinableVariadicFunctionType(Module &M, FunctionType *FTy) { + SmallVector<Type *> ArgTypes(FTy->param_begin(), FTy->param_end()); + ArgTypes.push_back(ABI.VAList->vaListParameterType(M)); + return FunctionType::get(FTy->getReturnType(), ArgTypes, + /*IsVarArgs*/ false); + } + + static ConstantInt *sizeOfAlloca(LLVMContext &Ctx, const DataLayout &DL, + AllocaInst *Alloced) { + Type *AllocaType = Alloced->getAllocatedType(); + TypeSize AllocaTypeSize = DL.getTypeAllocSize(AllocaType); + uint64_t AsInt = AllocaTypeSize.getFixedValue(); + return ConstantInt::get(Type::getInt64Ty(Ctx), AsInt); + } + + static SmallSet<unsigned, 2> supportedAddressSpaces(const DataLayout &DL) { + // FIXME: It looks like a module can contain arbitrary integers for address + // spaces in which case we might need to check _lots_ of cases. Maybe add a + // rule to the verifier that the vastart/vaend intrinsics can have arguments + // in 0 or in allocaaddrspace but nowhere else + SmallSet<unsigned, 2> Set; + Set.insert(0); // things tend to end up in zero + Set.insert( + DL.getAllocaAddrSpace()); // the argument should be in alloca addrspace + return Set; + } + + // this could be partially target specific + bool expansionApplicableToFunction(Module &M, Function *F) { + if (F->isIntrinsic() || !F->isVarArg() || + F->hasFnAttribute(Attribute::Naked)) { + return false; + } + + // TODO: work out what to do with the cs_chain functions documented as + // non-variadic that are variadic in some lit tests + if (F->getCallingConv() != CallingConv::C) + return false; + + if (!rewriteABI()) { + // e.g. can't replace a weak function unless changing the original symbol + if (GlobalValue::isInterposableLinkage(F->getLinkage())) { + return false; + } + } + + if (!rewriteABI()) { + // If optimising, err on the side of leaving things alone ---------------- arsenm wrote:
Move all this to an allUsesAreTrivialCalls helper function? https://github.com/llvm/llvm-project/pull/89007 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
