[compiler-rt][BF16] Provide __truncdfbf2 and __truncsfbf2 only when __bf16 is available

Differential Revision: https://reviews.llvm.org/D131147

compiler-rt/cmake/builtin-config-ix.cmake

@@ -30,6 +30,14 @@ _Float16 foo(_Float16 x) {
 "
 )
 
+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\");

compiler-rt/lib/builtins/CMakeLists.txt

@@ -165,10 +165,8 @@ set(GENERIC_SOURCES
   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 @@ set(GENERIC_SOURCES
   umodti3.c
 )
 
+# Build BF16 files only when "__bf16" is available.
+if(COMPILER_RT_HAS_BFLOAT16 AND NOT APPLE)
+  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

compiler-rt/lib/builtins/fp_trunc.h

@@ -60,7 +60,7 @@ typedef uint16_t dst_rep_t;
 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;