[clang] [llvm] [WIP] Expand variadic functions in IR (PR #89007)
Matt Arsenault via cfe-commits
cfe-commits at lists.llvm.org
Wed Apr 17 03:35:19 PDT 2024
================
@@ -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
+ for (const Use &U : F->uses()) {
+ const auto *CB = dyn_cast<CallBase>(U.getUser());
+
+ if (!CB)
+ return false;
+
+ if (CB->isMustTailCall())
+ return false;
+
+ if (!CB->isCallee(&U) ||
+ CB->getFunctionType() != F->getFunctionType()) {
+ return false;
+ }
+ }
+ }
+
+ // Branch funnels look like variadic functions but aren't:
+ //
+ // define hidden void @__typeid_typeid1_0_branch_funnel(ptr nest %0, ...) {
+ // musttail call void (...) @llvm.icall.branch.funnel(ptr %0, ptr @vt1_1,
+ // ptr @vf1_1, ...) ret void
+ // }
+ //
+ // %1 = call i32 @__typeid_typeid1_0_branch_funnel(ptr nest %vtable, ptr
+ // %obj, i32 1)
+ //
+ // If this function contains a branch funnel intrinsic, don't transform it.
+
+ if (Function *Funnel =
+ getPreexistingDeclaration(&M, Intrinsic::icall_branch_funnel)) {
+ for (const User *U : Funnel->users()) {
+ if (auto *I = dyn_cast<CallBase>(U)) {
+ if (F == I->getFunction()) {
+ return false;
+ }
+ }
+ }
+ }
+
+ return true;
+ }
+
+ bool callinstRewritable(CallBase *CB) {
+ if (CallInst *CI = dyn_cast<CallInst>(CB)) {
+ if (CI->isMustTailCall()) {
+ // Cannot expand musttail calls
+ if (rewriteABI()) {
+ // Todo: Sema?
+ report_fatal_error("Cannot lower musttail variadic call");
+ } else {
+ return false;
+ }
+ }
+ }
+
+ return true;
+ }
+
+ class ExpandedCallFrame {
+ // Helper for constructing an alloca instance containing the arguments bound
+ // to the variadic ... parameter, rearranged to allow indexing through a
+ // va_list iterator
+ //
+ // The awkward memory layout is to allow direct access to a contiguous array
+ // of types for the conversion to a struct type
+ enum { N = 4 };
+ SmallVector<Type *, N> FieldTypes;
+ enum Tag { IsByVal, NotByVal, Padding };
+ SmallVector<std::pair<Value *, Tag>, N> Fields;
+
+ template <Tag tag> void append(Type *T, Value *V) {
+ FieldTypes.push_back(T);
+ Fields.push_back({V, tag});
+ }
+
+ public:
+ void value(Type *T, Value *V) { append<NotByVal>(T, V); }
+
+ void byVal(Type *T, Value *V) { append<IsByVal>(T, V); }
+
+ void padding(LLVMContext &Ctx, uint64_t By) {
+ append<Padding>(ArrayType::get(Type::getInt8Ty(Ctx), By), nullptr);
+ }
+
+ size_t size() const { return FieldTypes.size(); }
+ bool empty() const { return FieldTypes.empty(); }
+
+ StructType *asStruct(LLVMContext &Ctx, StringRef Name) {
+ const bool IsPacked = true;
+ return StructType::create(Ctx, FieldTypes,
+ (Twine(Name) + ".vararg").str(), IsPacked);
+ }
+
+ void initialiseStructAlloca(const DataLayout &DL, IRBuilder<> &Builder,
+ AllocaInst *Alloced) {
+
+ StructType *VarargsTy = cast<StructType>(Alloced->getAllocatedType());
+
+ for (size_t I = 0; I < size(); I++) {
+ auto [V, tag] = Fields[I];
+ if (!V)
+ continue;
+
+ auto R = Builder.CreateStructGEP(VarargsTy, Alloced, I);
+ if (tag == IsByVal) {
+ Type *ByValType = FieldTypes[I];
+ Builder.CreateMemCpy(R, {}, V, {},
+ DL.getTypeAllocSize(ByValType).getFixedValue());
+ } else {
+ Builder.CreateStore(V, R);
+ }
+ }
+ }
+ };
+};
+
+bool ExpandVariadics::runOnModule(Module &M) {
+ bool Changed = false;
+ if (Mode == ExpandVariadicsMode::disable)
+ return Changed;
+
+ llvm::Triple Triple(M.getTargetTriple());
+
+ if (Triple.getArch() == Triple::UnknownArch) {
+ // If we don't know the triple, we can't lower varargs
+ return false;
+ }
+
+ ABI = VariadicABIInfo::create(Triple);
+ if (!ABI) {
+ if (Mode == ExpandVariadicsMode::lowering) {
+ report_fatal_error(
+ "Requested variadic lowering is unimplemented on this target");
+ }
+ return Changed;
+ }
+
+ const DataLayout &DL = M.getDataLayout();
+ auto &Ctx = M.getContext();
+ IRBuilder<> Builder(Ctx);
+
+ // At pass input, va_start intrinsics only occur in variadic functions, as
+ // checked by the IR verifier.
+
+ // The lowering pass needs to run on all variadic functions.
+ // The optimise could run on only those that call va_start
+ // in exchange for additional book keeping to avoid transforming
+ // the same function multiple times when it contains multiple va_start.
+ // Leaving that compile time optimisation for a later patch.
+ for (Function &F : llvm::make_early_inc_range(M))
+ Changed |= runOnFunction(M, Builder, &F);
+
+ // After runOnFunction, all known calls to known variadic functions have been
+ // replaced. va_start intrinsics are presently (and invalidly!) only present
+ // in functions thart used to be variadic and have now been mutated to take a
+ // va_list instead. If lowering as opposed to optimising, calls to unknown
+ // variadic functions have also been replaced.
+
+ // Warning: Intrinsics acting on other ones are missed
+ auto CandidateAddressSpaces = supportedAddressSpaces(DL);
+
+ for (unsigned Addrspace : CandidateAddressSpaces) {
+ PointerType *ArgType = PointerType::get(Ctx, Addrspace);
+ Changed |= expandIntrinsicUsers<Intrinsic::vastart, VAStartInst>(M, Builder,
+ ArgType);
+ Changed |=
+ expandIntrinsicUsers<Intrinsic::vaend, VAEndInst>(M, Builder, ArgType);
+ Changed |= expandIntrinsicUsers<Intrinsic::vacopy, VACopyInst>(M, Builder,
+ ArgType);
+ }
+
+ // Variadic intrinsics are now gone. The va_start have been replaced with the
+ // equivalent of a va_copy from the newly appended va_list argument, va_end
+ // and va_copy are removed. All that remains is for the lowering pass to find
+ // indirect calls and rewrite those as well.
+
+ if (Mode == ExpandVariadicsMode::lowering) {
+ for (Function &F : llvm::make_early_inc_range(M)) {
+ if (F.isDeclaration())
+ continue;
+
+ // Now need to track down indirect calls. Can't find those
+ // by walking uses of variadic functions, need to crawl the instruction
+ // stream. Fortunately this is only necessary for the ABI rewrite case.
+ for (BasicBlock &BB : F) {
+ for (Instruction &I : llvm::make_early_inc_range(BB)) {
+ if (CallBase *CB = dyn_cast<CallBase>(&I)) {
+ if (CB->isIndirectCall()) {
+ FunctionType *FTy = CB->getFunctionType();
+ if (FTy->isVarArg()) {
+ Changed |= expandCall(M, Builder, CB, FTy, 0);
+ }
+ }
+ }
+ }
+ }
+ }
+ }
+
+ return Changed;
+}
+
+bool ExpandVariadics::runOnFunction(Module &M, IRBuilder<> &Builder,
+ Function *F) {
+ bool Changed = false;
+
+ // fprintf(stderr, "Called runOn: %s\n", F->getName().str().c_str());
+
+ // This check might be too coarse - there are probably cases where
+ // splitting a function is bad but it's usable without splitting
+ if (!expansionApplicableToFunction(M, F))
+ return false;
+
+ // TODO: Leave "thunk" attribute functions alone?
+
+ // Need more tests than this. Weak etc. Some are in expansionApplicable.
+ if (F->isDeclaration() && !rewriteABI()) {
+ return false;
+ }
+
+ // TODO: Is the lazy construction here still useful?
+ Function *Equivalent = deriveInlinableVariadicFunctionPair(M, Builder, *F);
+
+ for (User *U : llvm::make_early_inc_range(F->users())) {
+ // TODO: A test where the call instruction takes a variadic function as
+ // a parameter other than the one it is calling
+ if (CallBase *CB = dyn_cast<CallBase>(U)) {
+ Value *calledOperand = CB->getCalledOperand();
+ if (F == calledOperand) {
+ Changed |= expandCall(M, Builder, CB, F->getFunctionType(), Equivalent);
+ }
+ }
+ }
+
+ if (rewriteABI()) {
+ // No direct calls remain to F, remaining uses are things like address
+ // escaping, modulo errors in this implementation.
+ for (User *U : llvm::make_early_inc_range(F->users()))
+ if (CallBase *CB = dyn_cast<CallBase>(U)) {
+ Value *calledOperand = CB->getCalledOperand();
+ if (F == calledOperand) {
+ report_fatal_error(
+ "ExpandVA abi requires eliminating call uses first\n");
+ }
+ }
+
+ Changed = true;
+ // Converting the original variadic function in-place into the equivalent
+ // one.
+ Equivalent->setLinkage(F->getLinkage());
+ Equivalent->setVisibility(F->getVisibility());
+ Equivalent->takeName(F);
+
+ // Indirect calls still need to be patched up
+ // DAE bitcasts it, todo: check block addresses
+ F->replaceAllUsesWith(Equivalent);
+ F->eraseFromParent();
+ }
+
+ return Changed;
+}
+
+Function *ExpandVariadics::deriveInlinableVariadicFunctionPair(
+ Module &M, IRBuilder<> &Builder, Function &F) {
+ // The purpose here is split the variadic function F into two functions
+ // One is a variadic function that bundles the passed argument into a va_list
+ // and passes it to the second function. The second function does whatever
+ // the original F does, except that it takes a va_list instead of the ...
+
+ assert(expansionApplicableToFunction(M, &F));
+
+ auto &Ctx = M.getContext();
+ const DataLayout &DL = M.getDataLayout();
+
+ // Returned value isDeclaration() is equal to F.isDeclaration()
+ // but that invariant is not satisfied throughout this function
+ const bool FunctionIsDefinition = !F.isDeclaration();
+
+ FunctionType *FTy = F.getFunctionType();
+ SmallVector<Type *> ArgTypes(FTy->param_begin(), FTy->param_end());
+ ArgTypes.push_back(ABI.VAList->vaListParameterType(M));
+
+ FunctionType *NFTy = inlinableVariadicFunctionType(M, F.getFunctionType());
+ Function *NF = Function::Create(NFTy, F.getLinkage(), F.getAddressSpace());
+
+ // Note - same attribute handling as DeadArgumentElimination
+ NF->copyAttributesFrom(&F);
+ NF->setComdat(F.getComdat()); // beware weak
+ F.getParent()->getFunctionList().insert(F.getIterator(), NF);
+ NF->setName(F.getName() + ".valist");
+ NF->IsNewDbgInfoFormat = F.IsNewDbgInfoFormat;
+
+ // New function is default visibility and internal
+ // Need to set visibility before linkage to avoid an assert in setVisibility
+ NF->setVisibility(GlobalValue::DefaultVisibility);
+ NF->setLinkage(GlobalValue::InternalLinkage);
+
+ AttrBuilder ParamAttrs(Ctx);
+ ParamAttrs.addAttribute(Attribute::NoAlias);
+
+ // TODO: When can the va_list argument have addAlignmentAttr called on it?
+ // It improves codegen lot in the non-inlined case. Probably target
+ // specific.
+
+ AttributeList Attrs = NF->getAttributes();
+ Attrs = Attrs.addParamAttributes(Ctx, NFTy->getNumParams() - 1, ParamAttrs);
+ NF->setAttributes(Attrs);
+
+ // Splice the implementation into the new function with minimal changes
+ if (FunctionIsDefinition) {
+ NF->splice(NF->begin(), &F);
+
+ auto NewArg = NF->arg_begin();
+ for (Argument &Arg : F.args()) {
+ Arg.replaceAllUsesWith(NewArg);
+ NewArg->setName(Arg.getName()); // takeName without killing the old one
+ ++NewArg;
+ }
+ NewArg->setName("varargs");
+ }
+
+ SmallVector<std::pair<unsigned, MDNode *>, 1> MDs;
+ F.getAllMetadata(MDs);
+ for (auto [KindID, Node] : MDs)
+ NF->addMetadata(KindID, *Node);
+
+ if (FunctionIsDefinition) {
+ // The blocks have been stolen so it's now a declaration
+ assert(F.isDeclaration());
+ Type *VaListTy = ABI.VAList->vaListType(Ctx);
+
+ auto *BB = BasicBlock::Create(Ctx, "entry", &F);
+ Builder.SetInsertPoint(BB);
+
+ Value *VaListInstance = Builder.CreateAlloca(VaListTy, nullptr, "va_list");
+
+ Builder.CreateIntrinsic(Intrinsic::vastart, {DL.getAllocaPtrType(Ctx)},
+ {VaListInstance});
+
+ SmallVector<Value *> Args;
+ for (Argument &A : F.args())
+ Args.push_back(&A);
+
+ // Shall we put the extra arg in alloca addrspace? Probably yes
+ VaListInstance = Builder.CreatePointerBitCastOrAddrSpaceCast(
+ VaListInstance, ABI.VAList->vaListParameterType(M));
+ Args.push_back(VaListInstance);
+
+ CallInst *Result = Builder.CreateCall(NF, Args);
+ Result->setTailCallKind(CallInst::TCK_Tail);
+
+ assert(ABI.VAList->vaEndIsNop()); // If this changes, insert a va_end here
+
+ if (Result->getType()->isVoidTy())
+ Builder.CreateRetVoid();
+ else
+ Builder.CreateRet(Result);
+ }
+
+ assert(F.isDeclaration() == NF->isDeclaration());
+
+ return NF;
+}
+
+bool ExpandVariadics::expandCall(Module &M, IRBuilder<> &Builder, CallBase *CB,
+ FunctionType *VarargFunctionType,
+ Function *NF) {
+ bool Changed = false;
+ const DataLayout &DL = M.getDataLayout();
+
+ if (!callinstRewritable(CB)) {
+ return Changed;
+ }
+
+ // This is something of a problem because the call instructions' idea of the
+ // function type doesn't necessarily match reality, before or after this
+ // pass
+ // Since the plan here is to build a new instruction there is no
+ // particular benefit to trying to preserve an incorrect initial type
+ // If the types don't match and we aren't changing ABI, leave it alone
+ // in case someone is deliberately doing dubious type punning through a
+ // varargs.
+ FunctionType *FuncType = CB->getFunctionType();
+ if (FuncType != VarargFunctionType) {
+ if (!rewriteABI()) {
+ return Changed;
+ }
+ FuncType = VarargFunctionType;
+ }
+
+ auto &Ctx = CB->getContext();
+
+ // Align the struct on ABI.MinAlign to start with
+ Align MaxFieldAlign(ABI.MinAlign ? ABI.MinAlign : 1);
+
+ // The strategy here is to allocate a call frame containing the variadic
+ // arguments laid out such that a target specific va_list can be initialised
+ // with it, such that target specific va_arg instructions will correctly
+ // iterate over it. Primarily this means getting the alignment right.
+
+ ExpandedCallFrame Frame;
+
+ uint64_t CurrentOffset = 0;
+ for (unsigned I = FuncType->getNumParams(), E = CB->arg_size(); I < E; ++I) {
+ Value *ArgVal = CB->getArgOperand(I);
+ bool IsByVal = CB->paramHasAttr(I, Attribute::ByVal);
+ Type *ArgType = IsByVal ? CB->getParamByValType(I) : ArgVal->getType();
+ Align DataAlign = DL.getABITypeAlign(ArgType);
+
+ uint64_t DataAlignV = DataAlign.value();
+
+ // Currently using 0 as a sentinel to mean ignored
+ if (ABI.MinAlign && DataAlignV < ABI.MinAlign)
+ DataAlignV = ABI.MinAlign;
+ if (ABI.MaxAlign && DataAlignV > ABI.MaxAlign)
+ DataAlignV = ABI.MaxAlign;
+
+ DataAlign = Align(DataAlignV);
+ MaxFieldAlign = std::max(MaxFieldAlign, DataAlign);
+
+ if (uint64_t Rem = CurrentOffset % DataAlignV) {
+ // Inject explicit padding to deal with alignment requirements
+ uint64_t Padding = DataAlignV - Rem;
+ Frame.padding(Ctx, Padding);
+ CurrentOffset += Padding;
+ }
+
+ if (IsByVal) {
+ Frame.byVal(ArgType, ArgVal);
+ } else {
+ Frame.value(ArgType, ArgVal);
+ }
+ CurrentOffset += DL.getTypeAllocSize(ArgType).getFixedValue();
+ }
+
+ if (Frame.empty()) {
+ // Not passing any arguments, hopefully va_arg won't try to read any
+ // Creating a single byte frame containing nothing to point the va_list
+ // instance as that is less special-casey in the compiler and probably
+ // easier to interpret in a debugger.
+ Frame.padding(Ctx, 1);
+ }
+
+ Function *CBF = CB->getParent()->getParent();
+
+ StructType *VarargsTy = Frame.asStruct(Ctx, CBF->getName());
+
+ // Put the alloca to hold the variadic args in the entry basic block.
+ // The clumsy construction is to set a the alignment on the instance
+ Builder.SetInsertPointPastAllocas(CBF);
+
+ // The struct instance needs to be at least MaxFieldAlign for the alignment of
+ // the fields to be correct at runtime. Use the native stack alignment instead
+ // if that's greater as that tends to give better codegen.
+ Align AllocaAlign = MaxFieldAlign;
+ if (DL.exceedsNaturalStackAlignment(Align(1024))) {
----------------
arsenm wrote:
Where did 1024 come from?
https://github.com/llvm/llvm-project/pull/89007
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