Re: [PATCH] Modify combine pattern by a pseudo AND with its nonzero bits [PR93453]

["Kewen.Lin" <linkw@linux.ibm.com>]

Hi Haochen,

on 2021/12/1 下午5:01, HAO CHEN GUI via Gcc-patches wrote:
> Hi,
>   This patch modifies the combine pattern with a helper - change_pseudo_and_mask when recog fails.
> The helper converts a single pseudo to the pseudo AND with a mask if the outer operator is IOR/XOR/PLUS
> and the inner operator is ASHIFT/LSHIFTRT/AND. The conversion helps match shift + ior pattern.
> 

Thanks for improving this!

I would expect this patch can make us remove the below existing splitting,
which was added for a similar purpose but only works for more insns
combination.

(define_split
  [(set (match_operand:GPR 0 "gpc_reg_operand")
	(plus_ior_xor:GPR (ashift:GPR (match_operand:GPR 1 "gpc_reg_operand")
				      (match_operand:SI 2 "const_int_operand"))
			  (match_operand:GPR 3 "gpc_reg_operand")))]
  "nonzero_bits (operands[3], <MODE>mode)
   < HOST_WIDE_INT_1U << INTVAL (operands[2])"
  [(set (match_dup 0)
	(ior:GPR (and:GPR (match_dup 3)
			  (match_dup 4))
		 (ashift:GPR (match_dup 1)
			     (match_dup 2))))]
{
  operands[4] = GEN_INT ((HOST_WIDE_INT_1U << INTVAL (operands[2])) - 1);
})


As the description, this seems to check some special operations and mainly
for those targets having Power style rotate* operations?  If the understanding
is correct, not sure it's a good idea to make this under a target hook/macro?


>   Bootstrapped and tested on powerpc64-linux BE and LE with no regressions. Is this okay for trunk?
> Any recommendations? Thanks a lot.
> 
> ChangeLog
> 2021-12-01 Haochen Gui <guihaoc@linux.ibm.com>
> 
> gcc/
> 	* combine.c (change_pseudo_and_mask): New.
> 	(recog_for_combine): If recog fails, try again with the pattern
> 	modified by change_pseudo_and_mask.
> 
> gcc/testsuite/
> 	* gcc.target/powerpc/20050603-3.c: Modify dump check conditions.
> 	* gcc.target/powerpc/rlwimi-2.c: Likewise.
> 
> 
> patch.diff
> diff --git a/gcc/combine.c b/gcc/combine.c
> index 03e9a780919..82ee3b2e9db 100644
> --- a/gcc/combine.c
> +++ b/gcc/combine.c
> @@ -11539,6 +11539,37 @@ change_zero_ext (rtx pat)
>    return changed;
>  }
> 
> +/* When the outer code of set_src is IOR/XOR/PLUS and the inner code is
> +   ASHIFT/LSHIFTRT/AND, convert a pseudo to psuedo AND with a mask if its
> +   nonzero_bits is less than its mode mask. The nonzero_bits in other pass
> +   doesn't return the same value as it does in combine pass.  */
> +static bool
> +change_pseudo_and_mask (rtx pat)
> +{
> +  bool changed = false;

Maybe we can remove this variable ...

> +
> +  rtx src = SET_SRC (pat);
> +  if ((GET_CODE (src) == IOR
> +       || GET_CODE (src) == XOR
> +       || GET_CODE (src) == PLUS)
> +      && (((GET_CODE (XEXP (src, 0)) == ASHIFT
> +	    || GET_CODE (XEXP (src, 0)) == LSHIFTRT
> +	    || GET_CODE (XEXP (src, 0)) == AND)
> +	   && REG_P (XEXP (src, 1)))))
> +    {
> +      rtx *reg = &XEXP (SET_SRC (pat), 1);
> +      machine_mode mode = GET_MODE (*reg);
> +      unsigned HOST_WIDE_INT nonzero = nonzero_bits (*reg, mode);
> +      if (nonzero < GET_MODE_MASK (mode))
> +	{
> +	  rtx x = gen_rtx_AND (mode, *reg, GEN_INT (nonzero));
> +	  SUBST (*reg, x);
> +	  changed = true;
    
..., directly return true here ...

> +	}
> +     }
> +  return changed;

and return false here.

> +}
> +
>  /* Like recog, but we receive the address of a pointer to a new pattern.
>     We try to match the rtx that the pointer points to.
>     If that fails, we may try to modify or replace the pattern,
> @@ -11586,7 +11617,14 @@ recog_for_combine (rtx *pnewpat, rtx_insn *insn, rtx *pnotes)
>  	    }
>  	}
>        else
> -	changed = change_zero_ext (pat);
> +	{
> +	  if (change_pseudo_and_mask (pat))
> +	    {
> +	      maybe_swap_commutative_operands (SET_SRC (pat));

maybe we can call maybe_swap_commutative_operands directly
in function change_pseudo_and_mask and make the code here compact.

BR,
Kewen

> +	      changed = true;
> +	    }
> +	  changed |= change_zero_ext (pat);
> +	}
>      }
>    else if (GET_CODE (pat) == PARALLEL)
>      {
> diff --git a/gcc/testsuite/gcc.target/powerpc/20050603-3.c b/gcc/testsuite/gcc.target/powerpc/20050603-3.c
> index 4017d34f429..e628be11532 100644
> --- a/gcc/testsuite/gcc.target/powerpc/20050603-3.c
> +++ b/gcc/testsuite/gcc.target/powerpc/20050603-3.c
> @@ -12,7 +12,7 @@ void rotins (unsigned int x)
>    b.y = (x<<12) | (x>>20);
>  }
> 
> -/* { dg-final { scan-assembler-not {\mrlwinm} } } */
> +/* { dg-final { scan-assembler-not {\mrlwinm} { target ilp32 } } } */
>  /* { dg-final { scan-assembler-not {\mrldic} } } */
>  /* { dg-final { scan-assembler-not {\mrot[lr]} } } */
>  /* { dg-final { scan-assembler-not {\ms[lr][wd]} } } */
> diff --git a/gcc/testsuite/gcc.target/powerpc/rlwimi-2.c b/gcc/testsuite/gcc.target/powerpc/rlwimi-2.c
> index bafa371db73..ffb5f9e450f 100644
> --- a/gcc/testsuite/gcc.target/powerpc/rlwimi-2.c
> +++ b/gcc/testsuite/gcc.target/powerpc/rlwimi-2.c
> @@ -2,14 +2,14 @@
>  /* { dg-options "-O2" } */
> 
>  /* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 14121 { target ilp32 } } } */
> -/* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 20217 { target lp64 } } } */
> +/* { dg-final { scan-assembler-times {(?n)^\s+[a-z]} 21279 { target lp64 } } } */
>  /* { dg-final { scan-assembler-times {(?n)^\s+blr} 6750 } } */
>  /* { dg-final { scan-assembler-times {(?n)^\s+mr} 643 { target ilp32 } } } */
>  /* { dg-final { scan-assembler-times {(?n)^\s+mr} 11 { target lp64 } } } */
>  /* { dg-final { scan-assembler-times {(?n)^\s+rldicl} 7790 { target lp64 } } } */
> 
>  /* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 1692 { target ilp32 } } } */
> -/* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 1666 { target lp64 } } } */
> +/* { dg-final { scan-assembler-times {(?n)^\s+rlwimi} 1692 { target lp64 } } } */
> 
>  /* { dg-final { scan-assembler-times {(?n)^\s+mulli} 5036 } } */
>