Re: [PATCH v2] Match: Support __builtin_add_overflow branch form for unsigned SAT_ADD

[Richard Biener <richard.guenther@gmail.com>]

On Fri, May 24, 2024 at 8:37 AM Li, Pan2 <pan2.li@intel.com> wrote:
>
> Thanks Jeff and Richard for suggestion and reviewing.
>
> Have another try in phiopt to do the convert from PHI to stmt = cond ? a : b.
> It can perform the convert from PHI to stmt = cond ? a : b successfully, and then
> the widen-mul is able to do the recog to .SAT_ADD.
>
> For now, to limit the risck, the above convert from PHI to stmt = cond ? a : b only be performed when matched,
> as well as the backend support the usadd standard name. Unfortunately, I am stuck in the case that when the lhs
> is not matched, we need to clean up something like created stmt in previous, or we will have ICE for missing definition.
>
> sat_add.c: In function ‘sat_add_u_3_uint8_t’:
> sat_add.c:69:1: error: missing definition
>    69 | SAT_ADD_U_3(uint8_t);
>       | ^~~~~~~~~~~
> for SSA_NAME: _6 in statement:
> # VUSE <.MEM_14(D)>
> return _6;
> during GIMPLE pass: phiopt
> dump file: sat_add.c.046t.phiopt1
> sat_add.c:69:1: internal compiler error: verify_ssa failed
> 0x1db41ba verify_ssa(bool, bool
> /home/pli/gcc/555/riscv-gnu-toolchain/gcc/__RISCV_BUILD__/../gcc/tree-ssa.cc:1203
> 0x18e3075 execute_function_todo
>         /home/pli/gcc/555/riscv-gnu-toolchain/gcc/__RISCV_BUILD__/../gcc/passes.cc:2096
> 0x18e1c52 do_per_function
>         /home/pli/gcc/555/riscv-gnu-toolchain/gcc/__RISCV_BUILD__/../gcc/passes.cc:1688
> 0x18e3222 execute_todo
>
> I bet the reason is that we created new stmt like stmt_cond and stmt_val but we don't insert it.
> Thus, there will be orphan nodes somewhere and we need something like rollback to recover the
> gimple up to a point. I tried sorts of release_xx or likewise but seems not working.
>
> So is there any suggest to take care of such gimple rollback or another solution for this? Below are
> The function to perform the convert from PHI to stmt = cond ? a : b for reference, thanks a lot.
>
> Pan
>
> diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> index 918cf50b589..7982b65bac4 100644
> --- a/gcc/tree-ssa-phiopt.cc
> +++ b/gcc/tree-ssa-phiopt.cc
> @@ -486,6 +486,88 @@ phiopt_early_allow (gimple_seq &seq, gimple_match_op &op)
>      }
>  }
>
> +extern bool gimple_unsigned_integer_sat_add (tree, tree*, tree (*)(tree));
> +
> +/* Try to match the phi expr to the gimple cond. Return true if we can
> +   perform the convert or return false.  There will be some restrictions
> +   or such kind of conversion, aka:
> +
> +   1. Only selected pattern will try this convert.
> +   2. The generated gassign matched the selected IFN pattern.
> +   3. The backend has implement the standard name.
> +
> +   From:
> +     <bb 2> :
> +     _1 = x_3(D) + y_4(D);
> +     if (_1 >= x_3(D))
> +       goto <bb 3>; [INV]
> +     else
> +       goto <bb 4>; [INV]
> +
> +     <bb 3> :
> +
> +     <bb 4> :
> +     # _2 = PHI <255(2), _1(3)>
> +
> +   To:
> +     <bb 2> :
> +     _1 = x_3(D) + y_4(D);
> +     phi_cond_6 = _1 >= x_3(D);
> +     _2 = phi_cond_6 ? _1 : 255; */
> +
> +static bool
> +match_phi_to_gimple_cond (basic_block cond_bb, gphi *phi, tree arg0, tree arg1)

You should do this in widen-mult and/or ISEL and if necessary for vectorization
in tree-if-conv.cc, though eventually what if-convert creates might be
good enough
to match during pattern recognition.

> +{
> +  gcond *cond = as_a <gcond *> (*gsi_last_bb (cond_bb));
> +
> +  if (!cond)
> +    return false;
> +
> +  enum tree_code code = gimple_cond_code (cond);
> +  tree phi_result = gimple_phi_result (phi);
> +  tree cond_tree = make_temp_ssa_name (boolean_type_node, NULL, "phi_cond");
> +  tree cmp_tree = build2 (code, boolean_type_node, gimple_cond_lhs (cond),
> +                         gimple_cond_rhs (cond));
> +  tree rhs = build3 (COND_EXPR, TREE_TYPE (phi_result), cond_tree, arg0, arg1);

phiopt directly uses cmp_tree, so you could do that as well and avoid stmt_cond.

> +
> +  gassign *stmt_cond = gimple_build_assign (cond_tree, cmp_tree);
> +  gassign *stmt_val = gimple_build_assign (phi_result, rhs);
> +
> +  tree ops[2];
> +  tree lhs = gimple_assign_lhs (stmt_val);
> +  bool matched_p = (gimple_unsigned_integer_sat_add (lhs, ops, NULL)
> +    && direct_internal_fn_supported_p (IFN_SAT_ADD, TREE_TYPE (lhs),
> +                                      OPTIMIZE_FOR_BOTH));
> +
> +  if (matched_p)
> +    {
> +      gimple_stmt_iterator gsi = gsi_last_bb (cond_bb);
> +      gimple_stmt_iterator psi = gsi_for_stmt (phi);
> +
> +      gsi_insert_before (&gsi, stmt_cond, GSI_SAME_STMT);
> +      gsi_insert_before (&gsi, stmt_val, GSI_SAME_STMT);
> +      remove_phi_node (&psi, false);

You only matched but you do not insert the actual .SAT_ADD here and that's
the definition that's missing.  You probably shouldn't need to add the
cond-stmt?

> +    }
> +  else
> +    {
> +      // Clean up the stmt created, but non of blow works well.
> +      // gsi = gsi_for_stmt (stmt_val);
> +      // gsi_remove (&gsi, true);
> +      // release_defs (stmt_val);
> +      // ggc_free (stmt_val);
> +
> +      // gsi = gsi_for_stmt (stmt_cond);
> +      // gsi_remove (&gsi, true);
> +      // release_defs (stmt_cond);
> +      // ggc_free (stmt_cond);
> +
> +      // release_defs (stmt_cond);
> +      // release_defs (stmt_val);
> +      release_ssa_name (cond_tree);

As you don't insert the stmts you should be able to simply
only release the SSA names and ggc_free the stmt.  You can also
look at maybe_fold_comparisons_from_match_pd in gimple-fold.cc
for more "ugly" ways to do this.

Building a helper in one place to match a PHI def as COND_EXPR
might be nice.  As said, avoiding all the mess by providing native
support from genmatch would be even better, but I'm not asking you
to do that.

Richard.

> +    }
> +
> +  return matched_p;
> +}
> +
> /* gimple_simplify_phiopt is like gimple_simplify but designed for PHIOPT.
>     Return NULL if nothing can be simplified or the resulting simplified value
>     with parts pushed if EARLY_P was true. Also rejects non allowed tree code
> @@ -826,6 +908,9 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
>       So, given the condition COND, and the two PHI arguments, match and simplify
>       can happen on (COND) ? arg0 : arg1. */
>
> +  if (match_phi_to_gimple_cond (cond_bb, phi, arg0, arg1))
> +    return true;
> +
>    stmt = last_nondebug_stmt (cond_bb);
>
>    /* We need to know which is the true edge and which is the false
>
>
> -----Original Message-----
> From: Jeff Law <jeffreyalaw@gmail.com>
> Sent: Thursday, May 23, 2024 10:59 PM
> To: Richard Biener <richard.guenther@gmail.com>; Li, Pan2 <pan2.li@intel.com>
> Cc: gcc-patches@gcc.gnu.org; juzhe.zhong@rivai.ai; kito.cheng@gmail.com; tamar.christina@arm.com; pinskia@gmail.com
> Subject: Re: [PATCH v2] Match: Support __builtin_add_overflow branch form for unsigned SAT_ADD
>
>
>
> On 5/23/24 6:14 AM, Richard Biener wrote:
> > On Thu, May 23, 2024 at 1:08 PM Li, Pan2 <pan2.li@intel.com> wrote:
> >>
> >> I have a try to convert the PHI from Part-A to Part-B, aka PHI to _2 = phi_cond ? _1 : 255.
> >> And then we can do the matching on COND_EXPR in the underlying widen-mul pass.
> >>
> >> Unfortunately, meet some ICE when verify_gimple_phi in sccopy1 pass =>
> >> sat_add.c:66:1: internal compiler error: tree check: expected class ‘type’, have ‘exceptional’ (error_mark) in useless_type_conversion_p, at gimple-expr.cc:86
> >
> > Likely you have released _2, more comments below on your previous mail.
> You can be sure by calling debug_tree () on the SSA_NAME node in
> question.  If it reports "in-free-list", then that's definitive that the
> SSA_NAME was released back to the SSA_NAME manager.  If that SSA_NAME is
> still in the IL, then that's very bad.
>
> jeff
>