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codegen: optimize returning an argument #33829

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Nov 18, 2019
Merged

codegen: optimize returning an argument #33829

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86 changes: 59 additions & 27 deletions src/codegen.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5209,7 +5209,7 @@ static Function *jl_cfunction_object(jl_value_t *ff, jl_value_t *declrt, jl_tupl
}

// generate a julia-callable function that calls f (AKA lam)
static Function *gen_invoke_wrapper(jl_method_instance_t *lam, jl_value_t *jlretty, const jl_returninfo_t &f, StringRef funcName, Module *M)
static Function *gen_invoke_wrapper(jl_method_instance_t *lam, jl_value_t *jlretty, const jl_returninfo_t &f, int retarg, StringRef funcName, Module *M)
{
Function *w = Function::Create(jl_func_sig, GlobalVariable::ExternalLinkage, funcName, M);
add_return_attr(w, Attribute::NonNull);
Expand All @@ -5234,7 +5234,7 @@ static Function *gen_invoke_wrapper(jl_method_instance_t *lam, jl_value_t *jlret
ctx.builder.SetCurrentDebugLocation(noDbg);
allocate_gc_frame(ctx, b0);

// TODO: replace this with emit_call_specfun_other
// TODO: replace this with emit_call_specfun_other?
FunctionType *ftype = f.decl->getFunctionType();
size_t nfargs = ftype->getNumParams();
Value **args = (Value**) alloca(nfargs * sizeof(Value*));
Expand Down Expand Up @@ -5270,7 +5270,7 @@ static Function *gen_invoke_wrapper(jl_method_instance_t *lam, jl_value_t *jlret
theArg = funcArg;
}
else {
Value *argPtr = ctx.builder.CreateInBoundsGEP(argArray, ConstantInt::get(T_size, i - 1));
Value *argPtr = ctx.builder.CreateConstInBoundsGEP1_32(T_prjlvalue, argArray, i - 1);
theArg = maybe_mark_load_dereferenceable(ctx.builder.CreateLoad(argPtr), false, ty);
}
if (!isboxed) {
Expand All @@ -5286,28 +5286,38 @@ static Function *gen_invoke_wrapper(jl_method_instance_t *lam, jl_value_t *jlret
call->setAttributes(f.decl->getAttributes());

jl_cgval_t retval;
switch (f.cc) {
case jl_returninfo_t::Boxed:
retval = mark_julia_type(ctx, call, true, jlretty);
break;
case jl_returninfo_t::Register:
retval = mark_julia_type(ctx, call, false, jlretty);
break;
case jl_returninfo_t::SRet:
retval = mark_julia_slot(result, jlretty, NULL, tbaa_stack);
break;
case jl_returninfo_t::Union:
// result is technically not right here, but `boxed` will only look at it
// for the unboxed values, so it's ok.
retval = mark_julia_slot(result,
jlretty,
ctx.builder.CreateExtractValue(call, 1),
tbaa_stack);
retval.Vboxed = ctx.builder.CreateExtractValue(call, 0);
break;
case jl_returninfo_t::Ghosts:
retval = mark_julia_slot(NULL, jlretty, call, tbaa_stack);
break;
if (retarg != -1) {
Value *theArg;
if (retarg == 0)
theArg = funcArg;
else
theArg = ctx.builder.CreateLoad(ctx.builder.CreateConstInBoundsGEP1_32(T_prjlvalue, argArray, retarg - 1));
retval = mark_julia_type(ctx, theArg, true, jl_any_type);
}
else {
switch (f.cc) {
case jl_returninfo_t::Boxed:
retval = mark_julia_type(ctx, call, true, jlretty);
break;
case jl_returninfo_t::Register:
retval = mark_julia_type(ctx, call, false, jlretty);
break;
case jl_returninfo_t::SRet:
retval = mark_julia_slot(result, jlretty, NULL, tbaa_stack);
break;
case jl_returninfo_t::Union:
// result is technically not right here, but `boxed` will only look at it
// for the unboxed values, so it's ok.
retval = mark_julia_slot(result,
jlretty,
ctx.builder.CreateExtractValue(call, 1),
tbaa_stack);
retval.Vboxed = ctx.builder.CreateExtractValue(call, 0);
break;
case jl_returninfo_t::Ghosts:
retval = mark_julia_slot(NULL, jlretty, call, tbaa_stack);
break;
}
}
ctx.builder.CreateRet(boxed(ctx, retval));
assert(!ctx.roots);
Expand Down Expand Up @@ -5641,9 +5651,31 @@ static std::unique_ptr<Module> emit_function(
has_sret = (returninfo.cc == jl_returninfo_t::SRet || returninfo.cc == jl_returninfo_t::Union);
jl_init_function(f);

// common pattern: see if all return statements are an argument in that
// case the apply-generic call can re-use the original box for the return
int retarg = [stmts, nreq]() {
int retarg = -1;
for (size_t i = 0; i < jl_array_len(stmts); ++i) {
jl_value_t *stmt = jl_array_ptr_ref(stmts, i);
if (jl_is_expr(stmt) && ((jl_expr_t*)stmt)->head == return_sym) {
stmt = jl_exprarg(stmt, 0);
if (!jl_is_slot(stmt))
return -1;
unsigned sl = jl_slot_number(stmt) - 1;
if (sl >= nreq)
return -1;
if (retarg == -1)
retarg = sl;
else if ((unsigned)retarg != sl)
return -1;
}
}
return retarg;
}();

std::stringstream wrapName;
wrapName << "jfptr_" << unadorned_name << "_" << globalUnique;
Function *fwrap = gen_invoke_wrapper(lam, jlrettype, returninfo, wrapName.str(), M);
Function *fwrap = gen_invoke_wrapper(lam, jlrettype, returninfo, retarg, wrapName.str(), M);
declarations->functionObject = strdup(fwrap->getName().str().c_str());
}
else {
Expand Down Expand Up @@ -6199,7 +6231,7 @@ static std::unique_ptr<Module> emit_function(
std::vector<Metadata*> scope_stack;
std::vector<MDNode*> scope_list_stack;
{
size_t nstmts = jl_array_len(src->code);
size_t nstmts = jl_array_len(stmts);
aliasscopes.resize(nstmts + 1, nullptr);
MDBuilder mbuilder(jl_LLVMContext);
MDNode *alias_domain = mbuilder.createAliasScopeDomain(ctx.name);
Expand Down
11 changes: 11 additions & 0 deletions test/compiler/codegen.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -392,6 +392,17 @@ end
f_dict_hash_alloc(); g_dict_hash_alloc();
@test (@allocated f_dict_hash_alloc()) == (@allocated g_dict_hash_alloc())

# returning an argument shouldn't alloc a new box
@noinline f33829(x) = (global called33829 = true; x)
g33829() = @allocated Base.inferencebarrier(f33829)(1.1,)
g33829() # warm up
@test (@allocated g33829()) == 0
@test called33829 # make sure there was a global side effect so it's hard for this call to simply be removed
let src = get_llvm(f33829, Tuple{Float64}, true, true)
@test occursin(r"call [^(]*double @", src)
@test !occursin(r"call [^(]*\%jl_value_t", src)
end

let io = IOBuffer()
# Test for the f(args...) = g(args...) generic codegen optimization
code_llvm(io, Base.vect, Tuple{Vararg{Union{Float64, Int64}}})
Expand Down