On Thu, Aug 5, 2021 at 9:25 AM Hongtao Liu <[email protected]> wrote:
>
> On Wed, Aug 4, 2021 at 7:28 PM Richard Biener
> <[email protected]> wrote:
> >
> > On Wed, Aug 4, 2021 at 4:39 AM Hongtao Liu <[email protected]> wrote:
> > >
> > > On Mon, Aug 2, 2021 at 2:31 PM liuhongt <[email protected]> wrote:
> > > >
> > > > gcc/ChangeLog:
> > > >
> > > > * config/i386/i386-modes.def (FLOAT_MODE): Define ieee HFmode.
> > > > * config/i386/i386.c (enum x86_64_reg_class): Add
> > > > X86_64_SSEHF_CLASS.
> > > > (merge_classes): Handle X86_64_SSEHF_CLASS.
> > > > (examine_argument): Ditto.
> > > > (construct_container): Ditto.
> > > > (classify_argument): Ditto, and set HFmode/HCmode to
> > > > X86_64_SSEHF_CLASS.
> > > > (function_value_32): Return _FLoat16/Complex Float16 by
> > > > %xmm0.
> > > > (function_value_64): Return _Float16/Complex Float16 by SSE
> > > > register.
> > > > (ix86_print_operand): Handle CONST_DOUBLE HFmode.
> > > > (ix86_secondary_reload): Require gpr as intermediate register
> > > > to store _Float16 from sse register when sse4 is not
> > > > available.
> > > > (ix86_libgcc_floating_mode_supported_p): Enable _FLoat16 under
> > > > sse2.
> > > > (ix86_scalar_mode_supported_p): Ditto.
> > > > (TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P): Defined.
> > > > * config/i386/i386.h (VALID_SSE2_REG_MODE): Add HFmode.
> > > > (VALID_INT_MODE_P): Add HFmode and HCmode.
> > > > * config/i386/i386.md (*pushhf_rex64): New define_insn.
> > > > (*pushhf): Ditto.
> > > > (*movhf_internal): Ditto.
> > > > * doc/extend.texi (Half-Precision Floating Point): Documemt
> > > > _Float16 for x86.
> > > > * emit-rtl.c (validate_subreg): Allow (subreg:SI (reg:HF) 0)
> > > > which is used by extract_bit_field but not backends.
> > > >
> > [...]
> > >
> > > Ping, i'd like to ask for approval for the below codes which is
> > > related to generic part.
> > >
> > > start from ..
> > > > diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
> > > > index ff3b4449b37..775ee397836 100644
> > > > --- a/gcc/emit-rtl.c
> > > > +++ b/gcc/emit-rtl.c
> > > > @@ -928,6 +928,11 @@ validate_subreg (machine_mode omode, machine_mode
> > > > imode,
> > > > fix them all. */
> > > > if (omode == word_mode)
> > > > ;
> > > > + /* ???Similarly like (subreg:DI (reg:SF), also allow (subreg:SI
> > > > (reg:HF))
> > > > + here. Though extract_bit_field is the culprit here, not the
> > > > backends. */
> > > > + else if (known_gt (regsize, osize) && known_gt (osize, isize)
> > > > + && FLOAT_MODE_P (imode) && INTEGRAL_MODE_P (omode))
> > > > + ;
> > > > /* ??? Similarly, e.g. with (subreg:DF (reg:TI)). Though
> > > > store_bit_field
> > > > is the culprit here, and not the backends. */
> > > > else if (known_ge (osize, regsize) && known_ge (isize, osize))
> > >
> > > and end here.
> >
> > So the main restriction otherwise in place is
> >
> > /* Subregs involving floating point modes are not allowed to
> > change size. Therefore (subreg:DI (reg:DF) 0) is fine, but
> > (subreg:SI (reg:DF) 0) isn't. */
> > else if (FLOAT_MODE_P (imode) || FLOAT_MODE_P (omode))
> > {
> > if (! (known_eq (isize, osize)
> > /* LRA can use subreg to store a floating point value in
> > an integer mode. Although the floating point and the
> > integer modes need the same number of hard registers,
> > the size of floating point mode can be less than the
> > integer mode. LRA also uses subregs for a register
> > should be used in different mode in on insn. */
> > || lra_in_progress))
> > return false;
> >
> > I'm not sure if it would be possible to do (subreg:SI (subreg:HI (reg:HF)))
>
> After debug, I find (subreg:SI (reg:HF)) is not really needed, it
> would be finally handled by below cut
> ----cut-----
> /* Find a correspondingly-sized integer field, so we can apply
> shifts and masks to it. */
> scalar_int_mode int_mode;
> if (!int_mode_for_mode (tmode).exists (&int_mode))
> /* If this fails, we should probably push op0 out to memory and then
> do a load. */
> int_mode = int_mode_for_mode (mode).require ();
>
> target = extract_fixed_bit_field (int_mode, op0, op0_mode, bitsize,
> bitnum, target, unsignedp, reverse);
> -----end----
>
> and generate things like below cut
>
> ---cut----
> (note 3 2 6 2 NOTE_INSN_FUNCTION_BEG)
> (insn 6 3 7 2 (parallel [
> (set (reg:HI 86)
> (and:HI (subreg:HI (reg/v:SI 83 [ a ]) 0)
> (const_int -1 [0xffffffffffffffff])))
> (clobber (reg:CC 17 flags))
> ])
> "../../gcc/x86-gcc/independentfp16/gcc/testsuite/gcc.target/i386/float16-5.c":11:11
> -1
> (nil))
> (insn 7 6 11 2 (set (reg:HF 82 [ <retval> ])
> (subreg:HF (reg:HI 86) 0))
> "../../gcc/x86-gcc/independentfp16/gcc/testsuite/gcc.target/i386/float16-5.c":11:11
> -1
> (nil))
> (insn 11 7 12 2 (set (reg/i:HF 20 xmm0)
> (reg:HF 82 [ <retval> ]))
> "../../gcc/x86-gcc/independentfp16/gcc/testsuite/gcc.target/i386/float16-5.c":12:1
> -1
> (nil))
> ----end---
>
> The real problem is here, when validate_subreg doesn't allow subreg
> between integer mode and float mode with different sizes. It will hit
> gcc_assert in gen_lowpart
>
> ----cut-----
> /* Don't use LHS paradoxical subreg if explicit truncation is needed
> between the mode of the extraction (word_mode) and the target
> mode. Instead, create a temporary and use convert_move to set
> the target. */
> if (REG_P (target)
> && TRULY_NOOP_TRUNCATION_MODES_P (GET_MODE (target), ext_mode))
> {
> target = gen_lowpart (ext_mode, target);
> if (partial_subreg_p (GET_MODE (spec_target), ext_mode))
> spec_target_subreg = target;
> }
> ----end----
>
> So how about changes like below, remove changes in validate_subreg and
> add some guard in extract_bit_field_using_extv.
>
> modified gcc/emit-rtl.c
> @@ -928,11 +928,6 @@ validate_subreg (machine_mode omode, machine_mode imode,
> fix them all. */
> if (omode == word_mode)
> ;
> - /* ???Similarly like (subreg:DI (reg:SF), also allow (subreg:SI (reg:HF))
> - here. Though extract_bit_field is the culprit here, not the backends.
> */
> - else if (known_gt (regsize, osize) && known_gt (osize, isize)
> - && FLOAT_MODE_P (imode) && INTEGRAL_MODE_P (omode))
> - ;
> /* ??? Similarly, e.g. with (subreg:DF (reg:TI)). Though store_bit_field
> is the culprit here, and not the backends. */
> else if (known_ge (osize, regsize) && known_ge (isize, osize))
> modified gcc/expmed.c
> @@ -1572,8 +1572,19 @@ extract_bit_field_using_extv (const
> extraction_insn *extv, rtx op0,
> between the mode of the extraction (word_mode) and the target
> mode. Instead, create a temporary and use convert_move to set
> the target. */
> + machine_mode tmode = GET_MODE (target);
> if (REG_P (target)
> - && TRULY_NOOP_TRUNCATION_MODES_P (GET_MODE (target), ext_mode))
> + && TRULY_NOOP_TRUNCATION_MODES_P (GET_MODE (target), ext_mode)
doesn't it simply mean that TRULY_NOOP_TRUNCATION_MODES_P may not be
true for modes that are not handled by gen_lowpart? But it just wraps the
truly_noop_truncation target hook which is fed the modes precision. In fact
I wonder why we're using 'extv' to "extract" sth larger from sth smaller at all.
Why do we arrive at something for get_best_reg_extraction_insn at all?
> + /* When validate_subreg doesn't allow subreg between integer mode
> + and float mode with different size, It will hit gcc_assert in
> + gen_lowpart_general. Also subreg like (subreg:DI (reg:SF)) is
> + not really needed, codes like below will be finally generated.
> + (set (reg:SI 1)
> + (and:SI (reg:DI 2) -1))
> + (set (reg:SF 3)
> + (subreg:SF (reg:SI 1))) */
> + && FLOAT_MODE_P (tmode) && INTEGRAL_MODE_P (mode)
> + && maybe_ne (GET_MODE_SIZE (tmode), GET_MODE_SIZE (mode)))
> {
> target = gen_lowpart (ext_mode, target);
> if (partial_subreg_p (GET_MODE (spec_target), ext_mode))
>
>
>
> > to "work around" this restriction. Alternatively one could finally do away
> > with all the exceptions and simply allow all such subregs giving them
> > semantics as to intermediate same-size subregs to integer modes
> > if this definition issue is why we disallow them?
> >
> > That is, any float-mode source or destination subreg is interpreted as
> > wrapping the source operand (if float-mode) in a same size int subreg
> > and performing the subreg in an integer mode first if the destination
> > mode is a float mode?
> >
> > Also I detest that validate_subreg list things not allowed as opposed
> > to things allowed. Why are FLOAT_MODE special, but
> > fractional and accumulating modes not? The subreg documentation
> > also doesn't talk about cases not allowed.
> >
> > Richard.
>
>
>
> --
> BR,
> Hongtao
