diff --git a/compiler-rt/cmake/builtin-config-ix.cmake b/compiler-rt/cmake/builtin-config-ix.cmake
--- a/compiler-rt/cmake/builtin-config-ix.cmake
+++ b/compiler-rt/cmake/builtin-config-ix.cmake
@@ -30,6 +30,14 @@
 "
 )
 
+builtin_check_c_compiler_source(COMPILER_RT_HAS_BFLOAT16
+"
+__bf16 foo(__bf16 x) {
+ return x;
+}
+"
+)
+
 builtin_check_c_compiler_source(COMPILER_RT_HAS_ASM_LSE
 "
 asm(\".arch armv8-a+lse\");
diff --git a/compiler-rt/lib/builtins/CMakeLists.txt b/compiler-rt/lib/builtins/CMakeLists.txt
--- a/compiler-rt/lib/builtins/CMakeLists.txt
+++ b/compiler-rt/lib/builtins/CMakeLists.txt
@@ -165,10 +165,8 @@
   subvsi3.c
   subvti3.c
   trampoline_setup.c
-  truncdfbf2.c
   truncdfhf2.c
   truncdfsf2.c
-  truncsfbf2.c
   truncsfhf2.c
   ucmpdi2.c
   ucmpti2.c
@@ -183,6 +181,15 @@
   umodti3.c
 )
 
+# Build BF16 files only when "__bf16" is available.
+if(COMPILER_RT_HAS_BFLOAT16)
+  set(GENERIC_SOURCES
+    ${GENERIC_SOURCES}
+    truncdfbf2.c
+    truncsfbf2.c
+  )
+endif()
+
 # TODO: Several "tf" files (and divtc3.c, but not multc3.c) are in
 # GENERIC_SOURCES instead of here.
 set(GENERIC_TF_SOURCES
@@ -699,6 +706,8 @@
 
   append_list_if(COMPILER_RT_HAS_FLOAT16 -DCOMPILER_RT_HAS_FLOAT16 BUILTIN_CFLAGS)
 
+  append_list_if(COMPILER_RT_HAS_BFLOAT16 -DCOMPILER_RT_HAS_BFLOAT16 BUILTIN_CFLAGS)
+
   append_list_if(COMPILER_RT_HAS_STD_C11_FLAG -std=c11 BUILTIN_CFLAGS)
 
   # These flags would normally be added to CMAKE_C_FLAGS by the llvm
diff --git a/compiler-rt/lib/builtins/fp_trunc.h b/compiler-rt/lib/builtins/fp_trunc.h
--- a/compiler-rt/lib/builtins/fp_trunc.h
+++ b/compiler-rt/lib/builtins/fp_trunc.h
@@ -60,7 +60,7 @@
 static const int dstSigBits = 10;
 
 #elif defined DST_BFLOAT
-typedef uint16_t dst_t;
+typedef __bf16 dst_t;
 typedef uint16_t dst_rep_t;
 #define DST_REP_C UINT16_C
 static const int dstSigBits = 7;