The folding of comparisons against Inf (to constants or comparisons
with the maximum finite value) has various cases where it introduces
or loses "invalid" exceptions for comparisons with NaNs.

Folding x > +Inf to 0 should not be about HONOR_SNANS - ordered
comparisons of both quiet and signaling NaNs should raise invalid.

x <= +Inf is not the same as x == x, because again that loses an
exception (equality comparisons don't raise exceptions except for
signaling NaNs).

x == +Inf is not the same as x > DBL_MAX, and a similar issue applies
with the x != +Inf case - that transformation causes a spurious
exception.

This patch fixes the conditionals on the folding to avoid such
introducing or losing exceptions.

Bootstrapped with no regressions on x86_64-pc-linux-gnu (where the
cases involving spurious exceptions wouldn't have failed anyway before
GCC 8 because of unordered comparisons wrongly always having formerly
been used by the back end).  Also tested for powerpc-linux-gnu
soft-float that this fixes many glibc math/ test failures that arose
in that configuration because this folding affected the IBM long
double support in libgcc (no such failures appeared for hard-float
because of the bug of powerpc hard-float always using unordered
comparisons) - some failures remain, but I believe them to be
unrelated.

	PR tree-optimization/64811
gcc:
	* match.pd: When optimizing comparisons with Inf, avoid
	introducing or losing exceptions from comparisons with NaN.

gcc/testsuite:
	* gcc.dg/torture/inf-compare-1.c, gcc.dg/torture/inf-compare-2.c,
	gcc.dg/torture/inf-compare-3.c, gcc.dg/torture/inf-compare-4.c,
	gcc.dg/torture/inf-compare-5.c, gcc.dg/torture/inf-compare-6.c,
	gcc.dg/torture/inf-compare-7.c, gcc.dg/torture/inf-compare-8.c:
	New tests.
	* gcc.c-torture/execute/ieee/fp-cmp-7.x: New file.

From-SVN: r256380