diff --git a/compiler-rt/lib/builtins/addtf3.c b/compiler-rt/lib/builtins/addtf3.c
--- a/compiler-rt/lib/builtins/addtf3.c
+++ b/compiler-rt/lib/builtins/addtf3.c
@@ -13,7 +13,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 #include "fp_add_impl.inc"
 
 COMPILER_RT_ABI fp_t __addtf3(fp_t a, fp_t b) {
diff --git a/compiler-rt/lib/builtins/comparetf2.c b/compiler-rt/lib/builtins/comparetf2.c
--- a/compiler-rt/lib/builtins/comparetf2.c
+++ b/compiler-rt/lib/builtins/comparetf2.c
@@ -39,7 +39,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 #include "fp_compare_impl.inc"
 
 COMPILER_RT_ABI CMP_RESULT __letf2(fp_t a, fp_t b) { return __leXf2__(a, b); }
diff --git a/compiler-rt/lib/builtins/divtf3.c b/compiler-rt/lib/builtins/divtf3.c
--- a/compiler-rt/lib/builtins/divtf3.c
+++ b/compiler-rt/lib/builtins/divtf3.c
@@ -14,7 +14,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 
 #define NUMBER_OF_HALF_ITERATIONS 4
 #define NUMBER_OF_FULL_ITERATIONS 1
diff --git a/compiler-rt/lib/builtins/extenddftf2.c b/compiler-rt/lib/builtins/extenddftf2.c
--- a/compiler-rt/lib/builtins/extenddftf2.c
+++ b/compiler-rt/lib/builtins/extenddftf2.c
@@ -9,7 +9,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 #define SRC_DOUBLE
 #define DST_QUAD
 #include "fp_extend_impl.inc"
diff --git a/compiler-rt/lib/builtins/extendhftf2.c b/compiler-rt/lib/builtins/extendhftf2.c
--- a/compiler-rt/lib/builtins/extendhftf2.c
+++ b/compiler-rt/lib/builtins/extendhftf2.c
@@ -10,8 +10,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT) &&                     \
-    defined(COMPILER_RT_HAS_FLOAT16)
+#if defined(CRT_HAS_TF_MODE) && defined(COMPILER_RT_HAS_FLOAT16)
 #define SRC_HALF
 #define DST_QUAD
 #include "fp_extend_impl.inc"
diff --git a/compiler-rt/lib/builtins/extendsftf2.c b/compiler-rt/lib/builtins/extendsftf2.c
--- a/compiler-rt/lib/builtins/extendsftf2.c
+++ b/compiler-rt/lib/builtins/extendsftf2.c
@@ -9,7 +9,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 #define SRC_SINGLE
 #define DST_QUAD
 #include "fp_extend_impl.inc"
diff --git a/compiler-rt/lib/builtins/fixtfdi.c b/compiler-rt/lib/builtins/fixtfdi.c
--- a/compiler-rt/lib/builtins/fixtfdi.c
+++ b/compiler-rt/lib/builtins/fixtfdi.c
@@ -9,7 +9,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 typedef di_int fixint_t;
 typedef du_int fixuint_t;
 #include "fp_fixint_impl.inc"
diff --git a/compiler-rt/lib/builtins/fixtfsi.c b/compiler-rt/lib/builtins/fixtfsi.c
--- a/compiler-rt/lib/builtins/fixtfsi.c
+++ b/compiler-rt/lib/builtins/fixtfsi.c
@@ -9,7 +9,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 typedef si_int fixint_t;
 typedef su_int fixuint_t;
 #include "fp_fixint_impl.inc"
diff --git a/compiler-rt/lib/builtins/fixtfti.c b/compiler-rt/lib/builtins/fixtfti.c
--- a/compiler-rt/lib/builtins/fixtfti.c
+++ b/compiler-rt/lib/builtins/fixtfti.c
@@ -9,7 +9,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 typedef ti_int fixint_t;
 typedef tu_int fixuint_t;
 #include "fp_fixint_impl.inc"
diff --git a/compiler-rt/lib/builtins/fixunstfdi.c b/compiler-rt/lib/builtins/fixunstfdi.c
--- a/compiler-rt/lib/builtins/fixunstfdi.c
+++ b/compiler-rt/lib/builtins/fixunstfdi.c
@@ -9,7 +9,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 typedef du_int fixuint_t;
 #include "fp_fixuint_impl.inc"
 
diff --git a/compiler-rt/lib/builtins/fixunstfsi.c b/compiler-rt/lib/builtins/fixunstfsi.c
--- a/compiler-rt/lib/builtins/fixunstfsi.c
+++ b/compiler-rt/lib/builtins/fixunstfsi.c
@@ -9,7 +9,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 typedef su_int fixuint_t;
 #include "fp_fixuint_impl.inc"
 
diff --git a/compiler-rt/lib/builtins/fixunstfti.c b/compiler-rt/lib/builtins/fixunstfti.c
--- a/compiler-rt/lib/builtins/fixunstfti.c
+++ b/compiler-rt/lib/builtins/fixunstfti.c
@@ -9,7 +9,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 typedef tu_int fixuint_t;
 #include "fp_fixuint_impl.inc"
 
diff --git a/compiler-rt/lib/builtins/floatditf.c b/compiler-rt/lib/builtins/floatditf.c
--- a/compiler-rt/lib/builtins/floatditf.c
+++ b/compiler-rt/lib/builtins/floatditf.c
@@ -15,7 +15,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 COMPILER_RT_ABI fp_t __floatditf(di_int a) {
 
   const int aWidth = sizeof a * CHAR_BIT;
diff --git a/compiler-rt/lib/builtins/floatsitf.c b/compiler-rt/lib/builtins/floatsitf.c
--- a/compiler-rt/lib/builtins/floatsitf.c
+++ b/compiler-rt/lib/builtins/floatsitf.c
@@ -15,7 +15,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 COMPILER_RT_ABI fp_t __floatsitf(si_int a) {
 
   const int aWidth = sizeof a * CHAR_BIT;
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
@@ -25,7 +25,7 @@
 // mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
 // mmmm mmmm mmmm
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 COMPILER_RT_ABI fp_t __floattitf(ti_int a) {
   if (a == 0)
     return 0.0;
diff --git a/compiler-rt/lib/builtins/floatunditf.c b/compiler-rt/lib/builtins/floatunditf.c
--- a/compiler-rt/lib/builtins/floatunditf.c
+++ b/compiler-rt/lib/builtins/floatunditf.c
@@ -15,7 +15,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 COMPILER_RT_ABI fp_t __floatunditf(du_int a) {
 
   const int aWidth = sizeof a * CHAR_BIT;
diff --git a/compiler-rt/lib/builtins/floatunsitf.c b/compiler-rt/lib/builtins/floatunsitf.c
--- a/compiler-rt/lib/builtins/floatunsitf.c
+++ b/compiler-rt/lib/builtins/floatunsitf.c
@@ -15,7 +15,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 COMPILER_RT_ABI fp_t __floatunsitf(su_int a) {
 
   const int aWidth = sizeof a * CHAR_BIT;
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
@@ -25,7 +25,7 @@
 // mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm
 // mmmm mmmm mmmm
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 COMPILER_RT_ABI fp_t __floatuntitf(tu_int a) {
   if (a == 0)
     return 0.0;
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
@@ -106,7 +106,12 @@
 
 #elif defined QUAD_PRECISION
 #if __LDBL_MANT_DIG__ == 113 && defined(__SIZEOF_INT128__)
+// TODO: Availability of the *tf functions should not depend on long double
+// being IEEE 128, but instead on being able to use a 128-bit floating-point
+// type, which includes __float128.
+// Right now this (incorrectly) stops the builtins from being used for x86.
 #define CRT_LDBL_128BIT
+#define CRT_HAS_TF_MODE
 #define TF_C(c) c##L
 typedef uint64_t half_rep_t;
 typedef __uint128_t rep_t;
diff --git a/compiler-rt/lib/builtins/multf3.c b/compiler-rt/lib/builtins/multf3.c
--- a/compiler-rt/lib/builtins/multf3.c
+++ b/compiler-rt/lib/builtins/multf3.c
@@ -14,7 +14,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 #include "fp_mul_impl.inc"
 
 COMPILER_RT_ABI fp_t __multf3(fp_t a, fp_t b) { return __mulXf3__(a, b); }
diff --git a/compiler-rt/lib/builtins/powitf2.c b/compiler-rt/lib/builtins/powitf2.c
--- a/compiler-rt/lib/builtins/powitf2.c
+++ b/compiler-rt/lib/builtins/powitf2.c
@@ -13,7 +13,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 
 // Returns: a ^ b
 
diff --git a/compiler-rt/lib/builtins/subtf3.c b/compiler-rt/lib/builtins/subtf3.c
--- a/compiler-rt/lib/builtins/subtf3.c
+++ b/compiler-rt/lib/builtins/subtf3.c
@@ -13,7 +13,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 COMPILER_RT_ABI fp_t __addtf3(fp_t a, fp_t b);
 
 // Subtraction; flip the sign bit of b and add.
diff --git a/compiler-rt/lib/builtins/trunctfdf2.c b/compiler-rt/lib/builtins/trunctfdf2.c
--- a/compiler-rt/lib/builtins/trunctfdf2.c
+++ b/compiler-rt/lib/builtins/trunctfdf2.c
@@ -9,7 +9,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 #define SRC_QUAD
 #define DST_DOUBLE
 #include "fp_trunc_impl.inc"
diff --git a/compiler-rt/lib/builtins/trunctfhf2.c b/compiler-rt/lib/builtins/trunctfhf2.c
--- a/compiler-rt/lib/builtins/trunctfhf2.c
+++ b/compiler-rt/lib/builtins/trunctfhf2.c
@@ -10,8 +10,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT) &&                     \
-    defined(COMPILER_RT_HAS_FLOAT16)
+#if defined(CRT_HAS_TF_MODE) && defined(COMPILER_RT_HAS_FLOAT16)
 #define SRC_QUAD
 #define DST_HALF
 #include "fp_trunc_impl.inc"
diff --git a/compiler-rt/lib/builtins/trunctfsf2.c b/compiler-rt/lib/builtins/trunctfsf2.c
--- a/compiler-rt/lib/builtins/trunctfsf2.c
+++ b/compiler-rt/lib/builtins/trunctfsf2.c
@@ -9,7 +9,7 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
+#if defined(CRT_HAS_TF_MODE)
 #define SRC_QUAD
 #define DST_SINGLE
 #include "fp_trunc_impl.inc"