On Fri, Apr 30, 2021 at 2:06 AM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> "H.J. Lu via Gcc-patches" <gcc-patches@gcc.gnu.org> writes:
> > gen_reg_rtx tracks stack alignment needed for pseudo registers so that
> > associated hard registers can be properly spilled onto stack. But there
> > are cases where associated hard registers will never be spilled onto
> > stack. gen_reg_rtx is changed to take an argument for register alignment
> > so that stack realignment can be avoided when not needed.
>
> How is it guaranteed that they will never be spilled though?
> I don't think that that guarantee exists for any kind of pseudo,
> except perhaps for the temporary pseudos that the RA creates to
> replace (match_scratch …)es.
>
The caller of creating pseudo registers with specific alignment must
guarantee that they will never be spilled. I am only using it in
/* Make operand1 a register if it isn't already. */
if (can_create_pseudo_p ()
&& !register_operand (op0, mode)
&& !register_operand (op1, mode))
{
/* NB: Don't increase stack alignment requirement when forcing
operand1 into a pseudo register to copy data from one memory
location to another since it doesn't require a spill. */
emit_move_insn (op0,
force_reg (GET_MODE (op0), op1,
(UNITS_PER_WORD * BITS_PER_UNIT)));
return;
}
for vector moves. RA shouldn't spill it.
> Thanks,
> Richard
>
> > * emit-rtl.c (gen_reg_rtx): Add an argument for register
> > alignment and use it if it isn't zero.
> > * explow.c (force_reg): Add an argument for register alignment
> > and pass it to gen_reg_rtx.
> > * explow.h (force_reg): Add an argument for register alignment
> > and default it to 0.
> > * expr.h (convert_to_mode): Likewise.
> > (convert_modes): Likewise.
> > * expr.c (convert_to_mode): Add an argument for register
> > alignment and pass it to convert_modes.
> > (convert_modes): Add an argument for register alignment and
> > pass it to gen_reg_rtx.
> > ---
> > gcc/emit-rtl.c | 5 +++--
> > gcc/explow.c | 6 +++---
> > gcc/explow.h | 2 +-
> > gcc/expr.c | 10 ++++++----
> > gcc/expr.h | 6 ++++--
> > gcc/rtl.h | 2 +-
> > 6 files changed, 18 insertions(+), 13 deletions(-)
> >
> > diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
> > index 07e908624a0..4accf851d23 100644
> > --- a/gcc/emit-rtl.c
> > +++ b/gcc/emit-rtl.c
> > @@ -1160,10 +1160,11 @@ subreg_memory_offset (const_rtx x)
> > This pseudo is assigned the next sequential register number. */
> >
> > rtx
> > -gen_reg_rtx (machine_mode mode)
> > +gen_reg_rtx (machine_mode mode, unsigned int align)
> > {
> > rtx val;
> > - unsigned int align = GET_MODE_ALIGNMENT (mode);
> > + if (align == 0)
> > + align = GET_MODE_ALIGNMENT (mode);
> >
> > gcc_assert (can_create_pseudo_p ());
> >
> > diff --git a/gcc/explow.c b/gcc/explow.c
> > index b6da277f689..c8673ce512d 100644
> > --- a/gcc/explow.c
> > +++ b/gcc/explow.c
> > @@ -663,7 +663,7 @@ copy_to_mode_reg (machine_mode mode, rtx x)
> > since we mark it as a "constant" register. */
> >
> > rtx
> > -force_reg (machine_mode mode, rtx x)
> > +force_reg (machine_mode mode, rtx x, unsigned int reg_align)
> > {
> > rtx temp, set;
> > rtx_insn *insn;
> > @@ -673,7 +673,7 @@ force_reg (machine_mode mode, rtx x)
> >
> > if (general_operand (x, mode))
> > {
> > - temp = gen_reg_rtx (mode);
> > + temp = gen_reg_rtx (mode, reg_align);
> > insn = emit_move_insn (temp, x);
> > }
> > else
> > @@ -683,7 +683,7 @@ force_reg (machine_mode mode, rtx x)
> > insn = get_last_insn ();
> > else
> > {
> > - rtx temp2 = gen_reg_rtx (mode);
> > + rtx temp2 = gen_reg_rtx (mode, reg_align);
> > insn = emit_move_insn (temp2, temp);
> > temp = temp2;
> > }
> > diff --git a/gcc/explow.h b/gcc/explow.h
> > index 698f2a2a21c..621cdd7d356 100644
> > --- a/gcc/explow.h
> > +++ b/gcc/explow.h
> > @@ -40,7 +40,7 @@ extern rtx copy_to_suggested_reg (rtx, rtx, machine_mode);
> >
> > /* Copy a value to a register if it isn't already a register.
> > Args are mode (in case value is a constant) and the value. */
> > -extern rtx force_reg (machine_mode, rtx);
> > +extern rtx force_reg (machine_mode, rtx, unsigned int reg_align = 0);
> >
> > /* Return given rtx, copied into a new temp reg if it was in memory. */
> > extern rtx force_not_mem (rtx);
> > diff --git a/gcc/expr.c b/gcc/expr.c
> > index b4c110f8c17..42db4ddbe0a 100644
> > --- a/gcc/expr.c
> > +++ b/gcc/expr.c
> > @@ -658,9 +658,10 @@ convert_mode_scalar (rtx to, rtx from, int unsignedp)
> > or by copying to a new temporary with conversion. */
> >
> > rtx
> > -convert_to_mode (machine_mode mode, rtx x, int unsignedp)
> > +convert_to_mode (machine_mode mode, rtx x, int unsignedp,
> > + unsigned int reg_align)
> > {
> > - return convert_modes (mode, VOIDmode, x, unsignedp);
> > + return convert_modes (mode, VOIDmode, x, unsignedp, reg_align);
> > }
> >
> > /* Return an rtx for a value that would result
> > @@ -674,7 +675,8 @@ convert_to_mode (machine_mode mode, rtx x, int
> > unsignedp)
> > You can give VOIDmode for OLDMODE, if you are sure X has a nonvoid
> > mode. */
> >
> > rtx
> > -convert_modes (machine_mode mode, machine_mode oldmode, rtx x, int
> > unsignedp)
> > +convert_modes (machine_mode mode, machine_mode oldmode, rtx x,
> > + int unsignedp, unsigned int reg_align)
> > {
> > rtx temp;
> > scalar_int_mode int_mode;
> > @@ -734,7 +736,7 @@ convert_modes (machine_mode mode, machine_mode oldmode,
> > rtx x, int unsignedp)
> > return simplify_gen_subreg (mode, x, oldmode, 0);
> > }
> >
> > - temp = gen_reg_rtx (mode);
> > + temp = gen_reg_rtx (mode, reg_align);
> > convert_move (temp, x, unsignedp);
> > return temp;
> > }
> > diff --git a/gcc/expr.h b/gcc/expr.h
> > index 9a2736f69fa..2b06da1a889 100644
> > --- a/gcc/expr.h
> > +++ b/gcc/expr.h
> > @@ -66,10 +66,12 @@ extern void init_expr (void);
> > extern void convert_move (rtx, rtx, int);
> >
> > /* Convert an rtx to specified machine mode and return the result. */
> > -extern rtx convert_to_mode (machine_mode, rtx, int);
> > +extern rtx convert_to_mode (machine_mode, rtx, int,
> > + unsigned int reg_align = 0);
> >
> > /* Convert an rtx to MODE from OLDMODE and return the result. */
> > -extern rtx convert_modes (machine_mode, machine_mode, rtx, int);
> > +extern rtx convert_modes (machine_mode, machine_mode, rtx, int,
> > + unsigned int reg_align = 0);
> >
> > /* Expand a call to memcpy or memmove or memcmp, and return the result. */
> > extern rtx emit_block_op_via_libcall (enum built_in_function, rtx, rtx,
> > rtx,
> > diff --git a/gcc/rtl.h b/gcc/rtl.h
> > index 398d745aff5..c72f7fd59b9 100644
> > --- a/gcc/rtl.h
> > +++ b/gcc/rtl.h
> > @@ -3125,7 +3125,7 @@ subreg_promoted_mode (rtx x)
> > /* In emit-rtl.c */
> > extern rtvec gen_rtvec_v (int, rtx *);
> > extern rtvec gen_rtvec_v (int, rtx_insn **);
> > -extern rtx gen_reg_rtx (machine_mode);
> > +extern rtx gen_reg_rtx (machine_mode, unsigned int align = 0);
> > extern rtx gen_rtx_REG_offset (rtx, machine_mode, unsigned int,
> > poly_int64);
> > extern rtx gen_reg_rtx_offset (rtx, machine_mode, int);
> > extern rtx gen_reg_rtx_and_attrs (rtx);
--
H.J.
