Improve codegen for Core.throw_methoderror and Core.current_scope

[topolarity]

This slightly improves our (LLVM) codegen for Core.throw_methoderror and Core.current_scope

julia> foo() = Core.current_scope()
julia> bar() = Core.throw_methoderror(+, nothing)

Before:

; Function Signature: foo()
define nonnull ptr @julia_foo_2488() #0 {
top:
  %0 = call ptr @jl_get_builtin_fptr(ptr nonnull @"+Core.#current_scope#2491.jit")
  %Builtin_ret = call nonnull ptr %0(ptr nonnull @"jl_global#2492.jit", ptr null, i32 0)
  ret ptr %Builtin_ret
}
; Function Signature: bar()
define void @julia_bar_589() #0 {
top:
  %jlcallframe1 = alloca [2 x ptr], align 8
  %0 = call ptr @jl_get_builtin_fptr(ptr nonnull @"+Core.#throw_methoderror#591.jit")
  %jl_nothing = load ptr, ptr @jl_nothing, align 8
  store ptr @"jl_global#593.jit", ptr %jlcallframe1, align 8
  %1 = getelementptr inbounds ptr, ptr %jlcallframe1, i64 1
  store ptr %jl_nothing, ptr %1, align 8
  %Builtin_ret = call nonnull ptr %0(ptr nonnull @"jl_global#592.jit", ptr nonnull %jlcallframe1, i32 2)
  call void @llvm.trap()
  unreachable
}

After:

; Function Signature: foo()
define nonnull ptr @julia_foo_713() #0 {
top:
  %thread_ptr = call ptr asm "movq %fs:0, $0", "=r"() #5
  %tls_ppgcstack = getelementptr inbounds i8, ptr %thread_ptr, i64 -8
  %tls_pgcstack = load ptr, ptr %tls_ppgcstack, align 8
  %current_scope = getelementptr inbounds i8, ptr %tls_pgcstack, i64 -72
  %0 = load ptr, ptr %current_scope, align 8
  ret ptr %0
}
; Function Signature: bar()
define void @julia_bar_1581() #0 {
top:
  %jlcallframe1 = alloca [2 x ptr], align 8
  %jl_nothing = load ptr, ptr @jl_nothing, align 8
  store ptr @"jl_global#1583.jit", ptr %jlcallframe1, align 8
  %0 = getelementptr inbounds ptr, ptr %jlcallframe1, i64 1
  store ptr %jl_nothing, ptr %0, align 8
  %jl_f_throw_methoderror_ret = call nonnull ptr @jl_f_throw_methoderror(ptr null, ptr nonnull %jlcallframe1, i32 2)
  call void @llvm.trap()
  unreachable
}

[topolarity]

@vtjnash Do you know why we don't just make builtin_func_map fully exhaustive (i.e. require all lookups to succeed)?

[vtjnash]

We certainly could. Just hasn't been done by anyone yet

[vtjnash]

We could also do better to inline that pointer, since we don't need to call jl_get_builtin_fptr when we could inline a load from the CodeInstance directly there

[topolarity]

Which CodeInstance?

[vtjnash]

The one in jl_get_builtin_fptr

[topolarity]

Ah right - but if we make builtin_func_map fully-exhaustive, then we should almost never use jl_get_builtin_fptr at runtime?

[gbaraldi]

Current scope should just be codegened to lower to just getting the scope out of the task. The fact it's a builtin is slightly annoying but it's fine.

julia/src/codegen.cpp

Lines 6789 to 6793 in 0073917

	static Value *get_scope_field(jl_codectx_t &ctx)
	{
	Value *ct = get_current_task(ctx);
	return emit_ptrgep(ctx, ct, offsetof(jl_task_t, scope), "current_scope");
	}

[topolarity]

Current scope should just be codegened to lower to just getting the scope out of the task

Done 👍