Add Type::int_with_byte_size constructor

cranelift/codegen/src/ir/types.rs

@@ -104,6 +104,8 @@ impl Type {
     }
 
     /// Get an integer type with the requested number of bits.
+    ///
+    /// For the same thing but in *bytes*, use [`Self::int_with_byte_size`].
     pub fn int(bits: u16) -> Option<Self> {
         match bits {
             8 => Some(I8),
@@ -115,6 +117,13 @@ impl Type {
         }
     }
 
+    /// Get an integer type with the requested number of bytes.
+    ///
+    /// For the same thing but in *bits*, use [`Self::int`].
+    pub fn int_with_byte_size(bytes: u16) -> Option<Self> {
+        Self::int(bytes.checked_mul(8)?)
+    }
+
     /// Get a type with the same number of lanes as `self`, but using `lane` as the lane type.
     fn replace_lanes(self, lane: Self) -> Self {
         debug_assert!(lane.is_lane() && !self.is_special());
@@ -595,4 +604,22 @@ mod tests {
         assert_eq!(B8.as_int(), I8);
         assert_eq!(B128.as_int(), I128);
     }
+
+    #[test]
+    fn int_from_size() {
+        assert_eq!(Type::int(0), None);
+        assert_eq!(Type::int(8), Some(I8));
+        assert_eq!(Type::int(33), None);
+        assert_eq!(Type::int(64), Some(I64));
+
+        assert_eq!(Type::int_with_byte_size(0), None);
+        assert_eq!(Type::int_with_byte_size(2), Some(I16));
+        assert_eq!(Type::int_with_byte_size(6), None);
+        assert_eq!(Type::int_with_byte_size(16), Some(I128));
+
+        // Ensure `int_with_byte_size` handles overflow properly
+        let evil = 0xE001_u16;
+        assert_eq!(evil.wrapping_mul(8), 8, "check the constant is correct");
+        assert_eq!(Type::int_with_byte_size(evil), None);
+    }
 }

cranelift/frontend/src/frontend.rs

@@ -13,6 +13,7 @@ use cranelift_codegen::ir::{
 };
 use cranelift_codegen::isa::TargetFrontendConfig;
 use cranelift_codegen::packed_option::PackedOption;
+use std::convert::TryInto; // FIXME: Remove in edition2021
 
 /// Structure used for translating a series of functions into Cranelift IR.
 ///
@@ -892,13 +893,7 @@ impl<'a> FunctionBuilder<'a> {
         }
 
         // Future work could consider expanding this to handle more-complex scenarios.
-        fn type_from_byte_size(size: u64) -> Option<Type> {
-            if size > 16 {
-                return None;
-            }
-            Type::int(size as u16 * 8)
-        }
-        if let Some(small_type) = type_from_byte_size(size) {
+        if let Some(small_type) = size.try_into().ok().and_then(Type::int_with_byte_size) {
             if let Equal | NotEqual = zero_cc {
                 let mut left_flags = flags;
                 if size == left_align.get().into() {