[PATCH][PR 57371] Remove useless floating point casts in comparisons

[Yuri Gribov <tetra2005 at gmail dot com>]

Hi all,

This is initial patch for
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57371 . Per Joseph's
suggestion it optimizes
  (float)lhs CMP rhs
  (double)lhs CMP rhs
to
  lhs CMP (typeof(x))rhs
whenever typeof(x) can be precisely represented by floating-point type
(e.g. short by float or int by double) and rhs can be precisely
represented by typeof(x).

Bootstrapped/regtested on x64. Ok for trunk?

I'd like to extend this further in follow-up patches:
1) fold always-false/always-true comparisons e.g.
  short x;
  (float)x > INT16_MAX;  // Always false
2) get rid of cast in comparisons with zero regardless of typeof(lhs)
when -fno-trapping-math:
  (float_or_double)lhs CMP 0

-Y

Attachment: pr57371-1.patch
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