On Mon, Jun 20, 2016 at 7:05 PM, H.J. Lu <[email protected]> wrote:
> Hi,
>
> This patch implements the alternate code sequence recommended in
>
> https://groups.google.com/forum/#!topic/x86-64-abi/de5_KnLHxtI
>
> to load external function address via GOT slot with
>
> movq func@GOTPCREL(%rip), %rax
>
> so that linker won't create an PLT entry for extern function
> address.
>
> Tested on x86-64. OK for trunk?
> + else if (ix86_force_load_from_GOT_p (op1))
> + {
> + /* Load the external function address via the GOT slot to
> + avoid PLT. */
> + op1 = gen_rtx_UNSPEC (Pmode, gen_rtvec (1, op1),
> + (TARGET_64BIT
> + ? UNSPEC_GOTPCREL
> + : UNSPEC_GOT));
> + op1 = gen_rtx_CONST (Pmode, op1);
> + op1 = gen_const_mem (Pmode, op1);
> + /* This symbol must be referenced via a load from the Global
> + Offset Table. */
> + set_mem_alias_set (op1, ix86_GOT_alias_set ());
> + op1 = convert_to_mode (mode, op1, 1);
> + op1 = force_reg (mode, op1);
> + emit_insn (gen_rtx_SET (op0, op1));
> + /* Generate a CLOBBER so that there will be no REG_EQUAL note
> + on the last insn to prevent cse and fwprop from replacing
> + a GOT load with a constant. */
> + rtx tmp = gen_reg_rtx (Pmode);
> + emit_clobber (tmp);
> + return;
Jeff, is this the recommended way to prevent CSE, as far as RTL
infrastructure is concerned? I didn't find any example of this
approach with other targets.
Uros.
