On Tue, Feb 17, 2015 at 11:39:34AM +0800, Terry Guo wrote:
> On Sun, Feb 15, 2015 at 7:35 PM, Segher Boessenkool
> <seg...@kernel.crashing.org> wrote:
> > Hi Terry,
> >
> > I still think this is stage1 material.
> >
> >> + /* Don't combine if dest contains a user specified register and i3
> >> contains
> >> + ASM_OPERANDS, because the user specified register (same with dest)
> >> in i3
> >> + would be replaced by the src of insn which might be different with
> >> + the user's expectation. */
> >
> > "Do not eliminate a register asm in an asm input" or similar? Text
> > explaining why REG_USERVAR_P && HARD_REGISTER_P works here would be
> > good to have, too.
> diff --git a/gcc/combine.c b/gcc/combine.c
> index f779117..aeb2854 100644
> --- a/gcc/combine.c
> +++ b/gcc/combine.c
> @@ -1779,7 +1779,7 @@ can_combine_p (rtx_insn *insn, rtx_insn *i3, rtx_insn
> *pred ATTRIBUTE_UNUSED,
> {
> int i;
> const_rtx set = 0;
> - rtx src, dest;
> + rtx src, dest, asm_op;
> rtx_insn *p;
> #ifdef AUTO_INC_DEC
> rtx link;
> @@ -1914,6 +1914,14 @@ can_combine_p (rtx_insn *insn, rtx_insn *i3, rtx_insn
> *pred ATTRIBUTE_UNUSED,
> set = expand_field_assignment (set);
> src = SET_SRC (set), dest = SET_DEST (set);
>
> + /* Use REG_USERVAR_P and HARD_REGISTER_P to check whether DEST is a user
> + specified register, and do not eliminate such register if it is in an
> + asm input because we may end up with something different with user's
> + expectation. */
That doesn't explain why this will hit (almost) only on register asms.
The user's expectation doesn't matter that much either: GCC would violate
its own documentation / promises, that matters more ;-)
> + if (REG_P (dest) && REG_USERVAR_P (dest) && HARD_REGISTER_P (dest)
> + && ((asm_op = extract_asm_operands (PATTERN (i3))) != NULL))
You do not need the temporary variable, nor the != 0 or the extra parens;
just write
&& extract_asm_operands (PATTERN (i3))
Cheers,
Segher
