tree-optimization/88540 - FP x > y ? x : y if-conversion without -ffast-math

tree-optimization/88540 - FP x > y ? x : y if-conversion without -ffast-math

The following makes sure that FP x > y ? x : y style max/min operations
are if-converted at the GIMPLE level.  While we can neither match
it to MAX_EXPR nor .FMAX as both have different semantics with IEEE
than the ternary ?: operation we can make sure to maintain this form
as a COND_EXPR so backends have the chance to match this to instructions
their ISA offers.

The patch does this in phiopt where we recognize min/max and instead
of giving up when we have to honor NaNs we alter the generated code
to a COND_EXPR.

This resolves PR88540 and we can then SLP vectorize the min operation
for its testcase.  It also resolves part of the regressions observed
with the change matching bit-inserts of bit-field-refs to vec_perm.

Expansion from a COND_EXPR rather than from compare-and-branch
gcc.target/i386/pr54855-9.c by producing extra moves while the
corresponding min/max operations are now already synthesized by
RTL expansion, register selection isn't optimal.  This can be also
provoked without this change by altering the operand order in the source.
I have XFAILed that part of the test.

	PR tree-optimization/88540
	* tree-ssa-phiopt.cc (minmax_replacement): Do not give up
	with NaNs but handle the simple case by if-converting to a
	COND_EXPR.

	* gcc.target/i386/pr88540.c: New testcase.
	* gcc.target/i386/pr54855-9.c: XFAIL check for redundant moves.
	* gcc.target/i386/pr54855-12.c: Adjust.
	* gcc.target/i386/pr54855-13.c: Likewise.
	* gcc.target/i386/pr110170.c: Likewise.
	* gcc.dg/tree-ssa/split-path-12.c: Likewise.