libm-test: Fix unintentional skips in `binop_common`

`binop_common` emits a `SKIP` that is intended to apply only to
`copysign`, but is instead applying to all binary operators. Correct the
general case but leave the currently-failing `maximum_num` tests as a
FIXME, to be resolved separately in [1].

Also simplify skip logic and NaN checking, and add a few more `copysign`
checks.

[1]: https://github.com/rust-lang/compiler-builtins/pull/939

1 files changed, 10 insertions, 5 deletions

diff --git a/library/compiler-builtins/libm-test/src/precision.rs b/library/compiler-builtins/libm-test/src/precision.rs
index f6cdd015a59..32825b15d47 100644
--- a/library/compiler-builtins/libm-test/src/precision.rs
+++ b/library/compiler-builtins/libm-test/src/precision.rs
@@ -444,13 +444,18 @@ fn binop_common<F1: Float, F2: Float>(
     expected: F2,
     ctx: &CheckCtx,
 ) -> CheckAction {
-    // MPFR only has one NaN bitpattern; allow the default `.is_nan()` checks to validate. Skip if
-    // the first input (magnitude source) is NaN and the output is also a NaN, or if the second
-    // input (sign source) is NaN.
-    if ctx.basis == CheckBasis::Mpfr
+    // MPFR only has one NaN bitpattern; skip tests in cases where the first argument would take
+    // the sign of a NaN second argument. The default NaN checks cover other cases.
+    if ctx.base_name == BaseName::Copysign && ctx.basis == CheckBasis::Mpfr && input.1.is_nan() {
+        return SKIP;
+    }
+
+    // FIXME(#939): this should not be skipped, there is a bug in our implementationi.
+    if ctx.base_name == BaseName::FmaximumNum
+        && ctx.basis == CheckBasis::Mpfr
         && ((input.0.is_nan() && actual.is_nan() && expected.is_nan()) || input.1.is_nan())
     {
-        return SKIP;
+        return XFAIL_NOCHECK;
     }
 
     /* FIXME(#439): our fmin and fmax do not compare signed zeros */