On Fri, Nov 3, 2017 at 6:13 PM, Jeff Law <l...@redhat.com> wrote: > On 11/03/2017 04:46 AM, Uros Bizjak wrote: >> >> 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 > > How about %esi in 32 bit mode and %rax in 64 bit mode? I think that avoids > hitting the parameter passing registers.
That is a good choice. IMO, It warrants a small comment, in the source, why this choice. Uros.
