Re: [PATCH] match.pd: Fix up sqrt (sqrt (x)) simplification [PR109301]

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Mar 28, 2023 at 08:57:12AM +0000, Richard Biener wrote:
> Hmm, but canonicalize_math_p () should be false after vectorization?
> 
> When we moved the pass we should have made sure to put the
> PROP_gimple_opt_math property set to pass_expand_powcabs instead.

Which pass is the one that actually canonicalizes the math such
that we want to keep its choices for later?
I must say I don't know the details why the sincos path has been
even moved.

> Now, the sqrt (sqrt ()) canonicalization to pow (.., 1./4) is
> probably invalid anyway, not sure if we can add a user-written
> vector sqrt testcase that would trigger during the canonicalization

How do we write user written vector sqrt?

> phase.  There are other uses of build_real that have the same
> issue - what's your conclusion this is never a problem there?

Looking through build_real* calls in match.pd, others are
either on simplifications of some expressions with REAL_CST operand
(so can't be vector then), or using
LOG*/EXP*/CBRT*/SIN*/ATAN*/COS*/POW*/CABS*/HYPOT*/POWI*/SIGNBIT*
calls in the expression being simplified, or this case.
I think no target provides vector optabs for those or they don't
have internal fns at all.
Maybe
(simplify
 /* signbit(x) -> x<0 if x doesn't have signed zeros.  */
 (SIGNBIT @0)
 (if (!HONOR_SIGNED_ZEROS (@0))
  (convert (lt @0 { build_real (TREE_TYPE (@0), dconst0); }))))
?

	Jakub