[Bug tree-optimization/94727] [10 Regression] GCC produces incorrect code with -O3 since r10-5071-g02d895504cc59be0

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94727

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to rsandifo@gcc.gnu.org from comment #5)
> Well, this is a bit of mess (surprise).  We have a "<" comparison
> between two booleans that are leaves of the SLP tree, so
> vectorizable_comparison falls back on:
> 
>   /* Invariant comparison.  */
>   if (!vectype)
>     {
>       vectype = get_vectype_for_scalar_type (vinfo, TREE_TYPE (rhs1),
>                                              slp_node);
>       if (maybe_ne (TYPE_VECTOR_SUBPARTS (vectype), nunits))
>         return false;
>     }
> 
> rhs1 and rhs2 are *unsigned* boolean types, so we get back a vector
> of unsigned integers.  All is well, and "<" works as expected without
> the need for:
> 
>   /* Boolean values may have another representation in vectors
>      and therefore we prefer bit operations over comparison for
>      them (which also works for scalar masks).  We store opcodes
>      to use in bitop1 and bitop2.  Statement is vectorized as
>        BITOP2 (rhs1 BITOP1 rhs2) or
>        rhs1 BITOP2 (BITOP1 rhs2)
>      depending on bitop1 and bitop2 arity.  */
>   bool swap_p = false;
>   if (VECTOR_BOOLEAN_TYPE_P (vectype))
>     {
> 
> However, we then defer to vect_get_slp_defs to get the actual operands.
> The expected vector type is not part of this interface.

Ah yeah - sth on my list to fix (not making the type part of that API
but assigning vector types to SLP nodes).  I even have partly completed
"hacks" to do that.  When we have (and use!) vector types on all SLP
nodes we can also get rid of the mismatch code.

> The request
> goes to vect_get_constant_vectors, which does:
> 
>   if (VECT_SCALAR_BOOLEAN_TYPE_P (TREE_TYPE (op))
>       && vect_mask_constant_operand_p (stmt_vinfo))
>     vector_type = truth_type_for (stmt_vectype);
>   else
>     vector_type = get_vectype_for_scalar_type (vinfo, TREE_TYPE (op),
> op_node);
> 
> So the function gives back a vector of mask types, which here are
> vectors of *signed* booleans.  This means that "<" gives:
> 
>   true (-1) < false (0)
> 
> and so the boolean fixup above was needed after all.
> 
> I'm going to try:
> 
> diff --git a/gcc/tree-vect-stmts.c b/gcc/tree-vect-stmts.c
> index 7f3a9fb5fb3..88a1e2c51d2 100644
> --- a/gcc/tree-vect-stmts.c
> +++ b/gcc/tree-vect-stmts.c
> @@ -10566,8 +10566,11 @@ vectorizable_comparison (stmt_vec_info stmt_info,
> gimple_stmt_iterator *gsi,
>    /* Invariant comparison.  */
>    if (!vectype)
>      {
> -      vectype = get_vectype_for_scalar_type (vinfo, TREE_TYPE (rhs1),
> -                                            slp_node);
> +      if (VECT_SCALAR_BOOLEAN_TYPE_P (TREE_TYPE (rhs1)))
> +       vectype = mask_type;
> +      else
> +       vectype = get_vectype_for_scalar_type (vinfo, TREE_TYPE (rhs1),
> +                                              slp_node);
>        if (!vectype || maybe_ne (TYPE_VECTOR_SUBPARTS (vectype), nunits))
>         return false;
>      }
> 
> which does at least fix the testcase.

LGTM.