On Mon, May 26, 2014 at 02:20:36PM -0400, Kai Tietz wrote:
> --- i386.c (revision 210936)
> +++ i386.c (working copy)
> @@ -5298,6 +5298,12 @@ ix86_function_ok_for_sibcall (tree decl, tree exp)
> decl_or_type = type;
> }
>
> + /* We need to reject stdarg-function for x86_64 ABI as accumulator
> + is used as argument. */
> + if (TARGET_64BIT && stdarg_p (type)
> + && ix86_function_type_abi (type) == SYSV_ABI)
> + return false;
> +
> /* Check that the return value locations are the same. Like
> if we are returning floats on the 80387 register stack, we cannot
> make a sibcall from a function that doesn't return a float to a
> @@ -24916,8 +24922,19 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx call
> ? !sibcall_insn_operand (XEXP (fnaddr, 0), word_mode)
> : !call_insn_operand (XEXP (fnaddr, 0), word_mode))
> {
> + rtx r;
> fnaddr = convert_to_mode (word_mode, XEXP (fnaddr, 0), 1);
> - fnaddr = gen_rtx_MEM (QImode, copy_to_mode_reg (word_mode, fnaddr));
> + if (!sibcall)
> + r = copy_to_mode_reg (word_mode, fnaddr);
> + else
> + {
> + r = gen_rtx_REG (word_mode, AX_REG);
> + if (! general_operand (fnaddr, VOIDmode))
> + fnaddr = force_operand (fnaddr, r);
Wrong formatting.
> + if (fnaddr != r)
> + emit_move_insn (r, fnaddr);
> + }
> + fnaddr = gen_rtx_MEM (QImode, r);
> }
>
> call = gen_rtx_CALL (VOIDmode, fnaddr, callarg1);
In any case, I still can't understand how limiting the choices of the
register allocator can improve code rather than making it worse.
If the accumulator is available there, why doesn't the RA choose it
if it is beneficial? And why aren't other registers similarly suitable for
that? Say r10, r11...
Jakub
