Add standard expansions for fcopysign.

This is also just a sign bit manipulation.

cranelift/filetests/wasm/f32-arith.cton

@@ -87,4 +87,9 @@ ebb0(v0: f32, v1: f32):
 
 ; function %f32_min(f32, f32) -> f32
 ; function %f32_max(f32, f32) -> f32
-; function %f32_copysign(f32, f32) -> f32
+
+function %f32_copysign(f32, f32) -> f32 {
+ebb0(v0: f32, v1: f32):
+    v2 = fcopysign v0, v1
+    return v2
+}

cranelift/filetests/wasm/f64-arith.cton

@@ -84,4 +84,9 @@ ebb0(v0: f64, v1: f64):
 
 ; function %f64_min(f64, f64) -> f64
 ; function %f64_max(f64, f64) -> f64
-; function %f64_copysign(f64, f64) -> f64
+
+function %f64_copysign(f64, f64) -> f64 {
+ebb0(v0: f64, v1: f64):
+    v2 = fcopysign v0, v1
+    return v2
+}

lib/cretonne/meta/base/legalize.py

@@ -226,3 +226,11 @@ for ty,             minus_zero in [
                 b << minus_zero,
                 a << bxor(x, b),
             ))
+    expand.legalize(
+            a << insts.fcopysign.bind(ty)(x, y),
+            Rtl(
+                b << minus_zero,
+                a1 << band_not(x, b),
+                a2 << band(y, b),
+                a << bor(a1, a2)
+            ))