================ @@ -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), ---------------- arsenm wrote:
Comment on where these magic expressions were derived? 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
