middle-end: Fix failures with bitclear patterns on signed values

middle-end: Fix failures with bitclear patterns on signed values

During testing after rebasing to commit I noticed a failing testcase with the
bitmask compare patch.

Consider the following C++ testcase:

#include <compare>

#define A __attribute__((noipa))
A bool f5 (double i, double j) { auto c = i <=> j; return c >= 0; }

This turns into a comparison against chars, on systems where chars are signed
the pattern inserts an unsigned convert such that it's able to do the
transformation.

i.e.:

  # RANGE [-1, 2]
  # c$_M_value_22 = PHI <-1(3), 0(2), 2(5), 1(4)>
  # RANGE ~[3, 254]
  _11 = (unsigned char) c$_M_value_22;
  _19 = _11 <= 1;
  # .MEM_24 = VDEF <.MEM_6(D)>
  D.10434 ={v} {CLOBBER};
  # .MEM_14 = VDEF <.MEM_24>
  D.10407 ={v} {CLOBBER};
  # VUSE <.MEM_14>
  return _19;

instead of:

  # RANGE [-1, 2]
  # c$_M_value_5 = PHI <-1(3), 0(2), 2(5), 1(4)>
  # RANGE [-2, 2]
  _3 = c$_M_value_5 & -2;
  _19 = _3 == 0;
  # .MEM_24 = VDEF <.MEM_6(D)>
  D.10440 ={v} {CLOBBER};
  # .MEM_14 = VDEF <.MEM_24>
  D.10413 ={v} {CLOBBER};
  # VUSE <.MEM_14>
  return _19;

This causes much worse codegen under -ffast-math due to phiops no longer
recognizing the pattern.  It turns out that phiopts spaceship_replacement is
looking for the exact form that was just changed.

The comments seems to suggest this code only checks for (res & ~1) == 0 but the
implementation seems to suggest it's broader.

As such I added a case to check to see if the value comparison we found is a
type cast.  and strips away the type cast and continues.

In match.pd the typecasts are only added for signed comparisons to == 0 and != 0
which are then rewritten into comparisons with 1.

As such I only check for 1 and LE and GT, which is what match.pd would have
rewritten it to.

This fixes the regression but this is not code I 100% understand, since I don't
really know the semantics of the spaceship operator so would appreciate an extra
look.

gcc/ChangeLog:

	* tree-ssa-phiopt.c (spaceship_replacement): Handle new canonical
	codegen.