Fix ImmLogic.invert(), and with it, fcopysign and float_misc test.

Previously, `fcopysign` was mysteriously failing to pass the
`float_misc` spec test. This was tracked down to bad logical-immediate
masks used to separate the sign and not-sign bits. In particular, the
masks for the and-not operations were wrong. The `invert()` function on
an `ImmLogic` immediate, it turns out, assumed every immediate would be
used by a 64-bit instruction; `ImmLogic` immediates are subtly different
for 32-bit instructions. This change tracks the instruction size (32 or
64 bits) intended for use with each such immediate, and passes it back
into `maybe_from_u64` when computing the inverted immediate.

Addresses several of the failures (`float_misc`, `f32_bitwise`) for
 #1521 (test failures) and presumably helps #1519 (SpiderMonkey
integration).

cranelift/codegen/src/isa/aarch64/inst/args.rs

@@ -6,6 +6,7 @@
 use crate::binemit::CodeOffset;
 use crate::ir::Type;
 use crate::isa::aarch64::inst::*;
+use crate::isa::aarch64::lower::ty_bits;
 
 use regalloc::{RealRegUniverse, Reg, Writable};
 
@@ -526,6 +527,19 @@ impl InstSize {
         }
     }
 
+    /// Convert from an integer type into the smallest size that fits.
+    pub fn from_ty(ty: Type) -> InstSize {
+        Self::from_bits(ty_bits(ty))
+    }
+
+    /// Convert to I32 or I64.
+    pub fn to_ty(self) -> Type {
+        match self {
+            InstSize::Size32 => I32,
+            InstSize::Size64 => I64,
+        }
+    }
+
     pub fn sf_bit(&self) -> u32 {
         match self {
             InstSize::Size32 => 0,