On Fri, Nov 3, 2017 at 11:14 AM, Richard Biener <richard.guent...@gmail.com> wrote: > On Fri, Nov 3, 2017 at 9:38 AM, Uros Bizjak <ubiz...@gmail.com> wrote: >>> * config/i386/i386.c (ix86_emit_restore_reg_using_pop): >>> Prototype. >>> (ix86_adjust_stack_and_probe_stack_clash): Use a push/pop >>> sequence >>> to probe at the start of a noreturn function. >>> >>> * gcc.target/i386/stack-check-12.c: New test >> >> - emit_stack_probe (plus_constant (Pmode, stack_pointer_rtx, >> - -GET_MODE_SIZE (word_mode))); >> + rtx_insn *insn = emit_insn (gen_push (gen_rtx_REG (word_mode, 0))); >> >> Please use AX_REG instead of 0. >> >> + RTX_FRAME_RELATED_P (insn) = 1; >> + ix86_emit_restore_reg_using_pop (gen_rtx_REG (word_mode, 0)); >> >> Also here. >> >> emit_insn (gen_blockage ()); >> >> BTW: Could we use an unused register here, if available? %eax is used >> to pass first argument in regparm functions on 32bit targets. > > Can you push %[er]sp? What about partial reg stalls when using other > registers (if the last set was a movb to it)? I guess [er]sp is safe here > as was [re]ax due to the ABI?
That would work, too. I believe, that this won't trigger stack engine [1], but since the operation is a bit unusual, let's ask HJ to be sure. [1] https://en.wikipedia.org/wiki/Stack_register#Stack_engine Uros.
