Add bypass for bf16 and bf16xN

Author: sayantn

compiler/rustc_codegen_llvm/src/abi.rs

@@ -368,6 +368,17 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
         }
 
         match self.type_kind(llvm_ty) {
+            TypeKind::BFloat => rust_ty == self.type_i16(),
+            TypeKind::Vector => {
+                let llvm_element_count = self.vector_length(llvm_ty) as u64;
+                let llvm_element_ty = self.element_type(llvm_ty);
+
+                if llvm_element_ty == self.type_bf16() {
+                    rust_ty == self.type_vector(self.type_i16(), llvm_element_count)
+                } else {
+                    false
+                }
+            }
             TypeKind::Struct if self.type_kind(rust_ty) == TypeKind::Struct => {
                 let rust_element_tys = self.struct_element_types(rust_ty);
                 let llvm_element_tys = self.struct_element_types(llvm_ty);

compiler/rustc_codegen_llvm/src/builder.rs

@@ -1698,7 +1698,7 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
                 }
                 ret
             }
-            _ => unreachable!(),
+            _ => self.bitcast(val, dest_ty), // for `bf16(xN)` <-> `u16(xN)`
         }
     }
 

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1050,6 +1050,9 @@ unsafe extern "C" {
     pub(crate) fn LLVMDoubleTypeInContext(C: &Context) -> &Type;
     pub(crate) fn LLVMFP128TypeInContext(C: &Context) -> &Type;
 
+    // Operations on non-IEEE real types
+    pub(crate) fn LLVMBFloatTypeInContext(C: &Context) -> &Type;
+
     // Operations on function types
     pub(crate) fn LLVMFunctionType<'a>(
         ReturnType: &'a Type,

compiler/rustc_codegen_llvm/src/type_.rs

@@ -168,6 +168,10 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
             )
         }
     }
+
+    pub(crate) fn type_bf16(&self) -> &'ll Type {
+        unsafe { llvm::LLVMBFloatTypeInContext(self.llcx()) }
+    }
 }
 
 impl<'ll, CX: Borrow<SCx<'ll>>> BaseTypeCodegenMethods for GenericCx<'ll, CX> {
@@ -241,7 +245,7 @@ impl<'ll, CX: Borrow<SCx<'ll>>> BaseTypeCodegenMethods for GenericCx<'ll, CX> {
 
     fn float_width(&self, ty: &'ll Type) -> usize {
         match self.type_kind(ty) {
-            TypeKind::Half => 16,
+            TypeKind::Half | TypeKind::BFloat => 16,
             TypeKind::Float => 32,
             TypeKind::Double => 64,
             TypeKind::X86_FP80 => 80,