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Multiversioning: support for aliases (from @ccallable) #37530

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Merged
merged 1 commit into from
Nov 25, 2021
Merged

Multiversioning: support for aliases (from @ccallable) #37530

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2 changes: 1 addition & 1 deletion src/codegen-stubs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ JL_DLLEXPORT void jl_dump_native_fallback(void *native_code,
const char *sysimg_data, size_t sysimg_len) UNAVAILABLE
JL_DLLEXPORT int32_t jl_get_llvm_gv_fallback(void *native_code, jl_value_t *p) UNAVAILABLE

JL_DLLEXPORT int jl_extern_c_fallback(jl_function_t *f, jl_value_t *rt, jl_value_t *argt, char *name) UNAVAILABLE
JL_DLLEXPORT void jl_extern_c_fallback(jl_function_t *f, jl_value_t *rt, jl_value_t *argt, char *name) UNAVAILABLE
JL_DLLEXPORT jl_value_t *jl_dump_method_asm_fallback(jl_method_instance_t *linfo, size_t world,
char raw_mc, char getwrapper, const char* asm_variant, const char *debuginfo, char binary) UNAVAILABLE
JL_DLLEXPORT jl_value_t *jl_dump_function_ir_fallback(void *f, char strip_ir_metadata, char dump_module, const char *debuginfo) UNAVAILABLE
Expand Down
73 changes: 65 additions & 8 deletions src/llvm-multiversioning.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -272,13 +272,13 @@ struct CloneCtx {
Constant *get_ptrdiff32(Constant *ptr, Constant *base) const;
template<typename T>
Constant *emit_offset_table(const std::vector<T*> &vars, StringRef name) const;
void rewrite_alias(GlobalAlias *alias, Function* F);

LLVMContext &ctx;
Type *T_size;
Type *T_int32;
Type *T_void;
PointerType *T_psize;
PointerType *T_pvoidfunc;
MDNode *tbaa_const;
MultiVersioning *pass;
std::vector<jl_target_spec_t> specs;
Expand All @@ -295,6 +295,8 @@ struct CloneCtx {
std::vector<std::pair<Constant*,uint32_t>> gv_relocs{};
// Mapping from function id (i.e. 0-based index in `fvars`) to GVs to be initialized.
std::map<uint32_t,GlobalVariable*> const_relocs;
// Functions that were referred to by a global alias, and might not have other uses.
std::set<uint32_t> alias_relocs;
bool has_veccall{false};
bool has_cloneall{false};
};
Expand Down Expand Up @@ -342,7 +344,6 @@ CloneCtx::CloneCtx(MultiVersioning *pass, Module &M)
T_int32(Type::getInt32Ty(ctx)),
T_void(Type::getVoidTy(ctx)),
T_psize(PointerType::get(T_size, 0)),
T_pvoidfunc(FunctionType::get(T_void, false)->getPointerTo()),
tbaa_const(tbaa_make_child("jtbaa_const", nullptr, true).first),
pass(pass),
specs(jl_get_llvm_clone_targets()),
Expand Down Expand Up @@ -702,6 +703,54 @@ Constant *CloneCtx::rewrite_gv_init(const Stack& stack)
return res;
}

// replace an alias to a function with a trampoline and (uninitialized) global variable slot
void CloneCtx::rewrite_alias(GlobalAlias *alias, Function *F)
{
assert(!is_vector(F->getFunctionType()));

Function *trampoline =
Function::Create(F->getFunctionType(), alias->getLinkage(), "", &M);
trampoline->copyAttributesFrom(F);
trampoline->takeName(alias);
alias->eraseFromParent();

uint32_t id;
GlobalVariable *slot;
std::tie(id, slot) = get_reloc_slot(F);
for (auto &grp: groups) {
grp.relocs.insert(id);
for (auto &tgt: grp.clones) {
tgt.relocs.insert(id);
}
}
alias_relocs.insert(id);

auto BB = BasicBlock::Create(ctx, "top", trampoline);
IRBuilder<> irbuilder(BB);

auto ptr = irbuilder.CreateLoad(F->getType(), slot);
ptr->setMetadata(llvm::LLVMContext::MD_tbaa, tbaa_const);
ptr->setMetadata(llvm::LLVMContext::MD_invariant_load, MDNode::get(ctx, None));

std::vector<Value *> Args;
for (auto &arg : trampoline->args())
Args.push_back(&arg);
auto call = irbuilder.CreateCall(F->getFunctionType(), ptr, makeArrayRef(Args));
if (F->isVarArg())
#if (defined(_CPU_ARM_) || defined(_CPU_PPC_) || defined(_CPU_PPC64_))
abort(); // musttail support is very bad on ARM, PPC, PPC64 (as of LLVM 3.9)
#else
call->setTailCallKind(CallInst::TCK_MustTail);
#endif
else
call->setTailCallKind(CallInst::TCK_Tail);

if (F->getReturnType() == T_void)
irbuilder.CreateRetVoid();
else
irbuilder.CreateRet(call);
}

void CloneCtx::fix_gv_uses()
{
auto single_pass = [&] (Function *orig_f) {
Expand All @@ -712,8 +761,14 @@ void CloneCtx::fix_gv_uses()
auto info = uses.get_info();
// We only support absolute pointer relocation.
assert(info.samebits);
// And only for non-constant global variable initializers
auto val = cast<GlobalVariable>(info.val);
GlobalVariable *val;
if (auto alias = dyn_cast<GlobalAlias>(info.val)) {
rewrite_alias(alias, orig_f);
continue;
}
else {
val = cast<GlobalVariable>(info.val);
}
assert(info.use->getOperandNo() == 0);
assert(!val->isConstant());
auto fid = get_func_id(orig_f);
Expand All @@ -739,8 +794,8 @@ std::pair<uint32_t,GlobalVariable*> CloneCtx::get_reloc_slot(Function *F)
auto id = get_func_id(F);
auto &slot = const_relocs[id];
if (!slot)
slot = new GlobalVariable(M, T_pvoidfunc, false, GlobalVariable::InternalLinkage,
ConstantPointerNull::get(T_pvoidfunc),
slot = new GlobalVariable(M, F->getType(), false, GlobalVariable::InternalLinkage,
ConstantPointerNull::get(F->getType()),
F->getName() + ".reloc_slot");
return std::make_pair(id, slot);
}
Expand Down Expand Up @@ -820,10 +875,9 @@ void CloneCtx::fix_inst_uses()
uint32_t id;
GlobalVariable *slot;
std::tie(id, slot) = get_reloc_slot(orig_f);
Instruction *ptr = new LoadInst(T_pvoidfunc, slot, "", false, insert_before);
Instruction *ptr = new LoadInst(orig_f->getType(), slot, "", false, insert_before);
ptr->setMetadata(llvm::LLVMContext::MD_tbaa, tbaa_const);
ptr->setMetadata(llvm::LLVMContext::MD_invariant_load, MDNode::get(ctx, None));
ptr = new BitCastInst(ptr, F->getType(), "", insert_before);
use_i->setOperand(info.use->getOperandNo(),
rewrite_inst_use(uses.get_stack(), ptr,
insert_before));
Expand Down Expand Up @@ -951,6 +1005,9 @@ void CloneCtx::emit_metadata()
values.push_back(id_v);
values.push_back(get_ptrdiff32(it->second, gbase));
}
if (alias_relocs.find(id) != alias_relocs.end()) {
shared_relocs.insert(id);
}
}
values[0] = ConstantInt::get(T_int32, values.size() / 2);
ArrayType *vars_type = ArrayType::get(T_int32, values.size());
Expand Down