diff --git a/compiler-rt/lib/builtins/floattitf.c b/compiler-rt/lib/builtins/floattitf.c
--- a/compiler-rt/lib/builtins/floattitf.c
+++ b/compiler-rt/lib/builtins/floattitf.c
@@ -26,6 +26,9 @@
 // mmmm mmmm mmmm
 
 #if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(__clang__) && defined(__sparc__)
+#pragma clang optimize off
+#endif
 COMPILER_RT_ABI fp_t __floattitf(ti_int a) {
   if (a == 0)
     return 0.0;
@@ -74,5 +77,8 @@
   fb.u.low.all = (du_int)(a);
   return fb.f;
 }
+#if defined(__clang__) && defined(__sparc__)
+#pragma clang optimize on
+#endif
 
 #endif
diff --git a/compiler-rt/lib/builtins/floatuntitf.c b/compiler-rt/lib/builtins/floatuntitf.c
--- a/compiler-rt/lib/builtins/floatuntitf.c
+++ b/compiler-rt/lib/builtins/floatuntitf.c
@@ -26,6 +26,9 @@
 // mmmm mmmm mmmm
 
 #if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(__clang__) && defined(__sparc__)
+#pragma clang optimize off
+#endif
 COMPILER_RT_ABI fp_t __floatuntitf(tu_int a) {
   if (a == 0)
     return 0.0;
@@ -71,5 +74,8 @@
   fb.u.low.all = (du_int)(a);
   return fb.f;
 }
+#if defined(__clang__) && defined(__sparc__)
+#pragma clang optimize on
+#endif
 
 #endif
diff --git a/compiler-rt/lib/builtins/fp_extend.h b/compiler-rt/lib/builtins/fp_extend.h
--- a/compiler-rt/lib/builtins/fp_extend.h
+++ b/compiler-rt/lib/builtins/fp_extend.h
@@ -83,6 +83,9 @@
   return rep.i;
 }
 
+#if defined(__clang__) && defined(__sparc__)
+#pragma clang optimize off
+#endif
 static __inline dst_t dstFromRep(dst_rep_t x) {
   const union {
     dst_t f;
@@ -90,6 +93,9 @@
   } rep = {.i = x};
   return rep.f;
 }
+#if defined(__clang__) && defined(__sparc__)
+#pragma clang optimize on
+#endif
 // End helper routines.  Conversion implementation follows.
 
 #endif // FP_EXTEND_HEADER
diff --git a/compiler-rt/lib/builtins/fp_lib.h b/compiler-rt/lib/builtins/fp_lib.h
--- a/compiler-rt/lib/builtins/fp_lib.h
+++ b/compiler-rt/lib/builtins/fp_lib.h
@@ -230,6 +230,10 @@
   return rep.i;
 }
 
+// Work around miscompilation on sparcv9 (Bug 47729).
+#if defined(__clang__) && defined(__sparc__)
+#pragma clang optimize off
+#endif
 static __inline fp_t fromRep(rep_t x) {
   const union {
     fp_t f;
@@ -237,6 +241,9 @@
   } rep = {.i = x};
   return rep.f;
 }
+#if defined(__clang__) && defined(__sparc__)
+#pragma clang optimize on
+#endif
 
 static __inline int normalize(rep_t *significand) {
   const int shift = rep_clz(*significand) - rep_clz(implicitBit);