c2rust-transpile: add partial bfloat16 support

like Half, this is basically just a stub for now

supporting these types properly could use the `half` crate, but this is just to get basic AArch64 translation working

this type was also added in Clang/LLVM 11, so ifdef'd accordingly

we need to handle these now because ARMv8.6-a adds the BFloat16/__bf16 type as a vector element of one of the SVE vector types just added

Author: fw-immunant

c2rust-ast-exporter/src/AstExporter.cpp

@@ -364,6 +364,9 @@ class TypeEncoder final : public TypeVisitor<TypeEncoder> {
         case BuiltinType::ULong:      tag = TagULong;       break;
         case BuiltinType::ULongLong:  tag = TagULongLong;   break;
         case BuiltinType::Half:       tag = TagHalf;        break;
+        #if CLANG_VERSION_MAJOR >= 11
+        case BuiltinType::BFloat16:   tag = TagBFloat16;    break;
+        #endif
         case BuiltinType::Float:      tag = TagFloat;       break;
         case BuiltinType::Double:     tag = TagDouble;      break;
         case BuiltinType::LongDouble: tag = TagLongDouble;  break;

c2rust-ast-exporter/src/ast_tags.hpp

@@ -141,6 +141,7 @@ enum TypeTag {
     TagBlockPointer,
     TagComplexType,
     TagHalf,
+    TagBFloat16,
 };
 
 enum StringTypeTag {

c2rust-transpile/src/c_ast/conversion.rs

@@ -578,6 +578,11 @@ impl ConversionContext {
                     self.processed_nodes.insert(new_id, OTHER_TYPE);
                 }
 
+                TypeTag::TagBFloat16 if expected_ty & OTHER_TYPE != 0 => {
+                    self.add_type(new_id, not_located(CTypeKind::BFloat16));
+                    self.processed_nodes.insert(new_id, OTHER_TYPE);
+                }
+
                 TypeTag::TagInt128 if expected_ty & OTHER_TYPE != 0 => {
                     self.add_type(new_id, not_located(CTypeKind::Int128));
                     self.processed_nodes.insert(new_id, OTHER_TYPE);
@@ -783,6 +788,12 @@ impl ConversionContext {
                     self.processed_nodes.insert(new_id, OTHER_TYPE);
                 }
 
+                TypeTag::TagBFloat16 => {
+                    let ty = CTypeKind::BuiltinFn;
+                    self.add_type(new_id, not_located(ty));
+                    self.processed_nodes.insert(new_id, OTHER_TYPE);
+                }
+
                 TypeTag::TagVectorType => {
                     let elt = from_value(ty_node.extras[0].clone()).expect("Vector child not found");
                     let elt_new = self.visit_qualified_type(elt);

c2rust-transpile/src/c_ast/iterators.rs

@@ -267,7 +267,8 @@ fn immediate_type_children(kind: &CTypeKind) -> Vec<SomeId> {
         Elaborated(_) => vec![], // These are references to previous definitions
         TypeOfExpr(e) => intos![e],
         Void | Bool | Short | Int | Long | LongLong | UShort | UInt | ULong | ULongLong | SChar
-        | UChar | Char | Double | LongDouble | Float | Int128 | UInt128 | BuiltinFn | Half => {
+        | UChar | Char | Double | LongDouble | Float | Int128 | UInt128 | BuiltinFn | Half
+        | BFloat16 => {
             vec![]
         }
 

c2rust-transpile/src/c_ast/mod.rs

@@ -1577,6 +1577,7 @@ pub enum CTypeKind {
     Vector(CQualTypeId, usize),
 
     Half,
+    BFloat16,
 }
 
 #[derive(Copy, Clone, Debug)]

c2rust-transpile/src/convert_type.rs

@@ -332,7 +332,7 @@ impl TypeConverter {
             CTypeKind::LongDouble => Ok(mk().path_ty(mk().path(vec!["f128", "f128"]))),
             CTypeKind::Float => Ok(mk().path_ty(mk().path(vec!["libc", "c_float"]))),
             CTypeKind::Int128 => Ok(mk().path_ty(mk().path(vec!["i128"]))),
-            CTypeKind::UInt128 => Ok(mk().path_ty(mk().path(vec!["u128"]))),
+            CTypeKind::UInt128 => Ok(mk().path_ty(mk().path(vec!["bf16"]))),
 
             CTypeKind::Pointer(qtype) => self.convert_pointer(ctxt, qtype),
 

c2rust-transpile/src/translator/mod.rs

@@ -4675,7 +4675,7 @@ impl<'c> Translation<'c> {
         match type_kind {
             // libc can be accessed from anywhere as of Rust 2019 by full path
             Void | Char | SChar | UChar | Short | UShort | Int | UInt | Long | ULong | LongLong
-            | ULongLong | Int128 | UInt128 | Half | Float | Double | LongDouble => {}
+            | ULongLong | Int128 | UInt128 | Half | BFloat16 | Float | Double | LongDouble => {}
             // Bool uses the bool type, so no dependency on libc
             Bool => {}
             Paren(ctype)