Cranelift AArch64: Improve the type checks for IR operations

There were cases where the AArch64 backend assumed that an IR
operation would always operate on certain types (the most likely
reason being that the corresponding WebAssembly instruction did
not cover anything else), even though the definition of the IR
operation imposed no constraints like that.

Copyright (c) 2021, Arm Limited.

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

@@ -550,6 +550,8 @@ impl OperandSize {
 
     /// Convert from an integer type into the smallest size that fits.
     pub fn from_ty(ty: Type) -> OperandSize {
+        debug_assert!(!ty.is_vector());
+
         Self::from_bits(ty_bits(ty))
     }
 
@@ -611,6 +613,8 @@ impl ScalarSize {
 
     /// Convert from a type into the smallest size that fits.
     pub fn from_ty(ty: Type) -> ScalarSize {
+        debug_assert!(!ty.is_vector());
+
         Self::from_bits(ty_bits(ty))
     }
 
@@ -655,6 +659,8 @@ impl VectorSize {
 
     /// Convert from a type into a vector operand size.
     pub fn from_ty(ty: Type) -> VectorSize {
+        debug_assert!(ty.is_vector());
+
         match ty {
             B8X16 => VectorSize::Size8x16,
             B16X8 => VectorSize::Size16x8,