[compiler-rt] [builtins] Detect _Float16 support at compile time

[dim]

Summary

Instead of detecting _Float16 support at CMake configuration time,
detect it at compile time by checking for the predefined (by the
compiler) macro __FLT16_MAX__ instead.

This solves the issue where compiler-rt is built simultaneously for both
x86_64 and i386 targets, and the CMake configuration uses x86_64
compilation to detect _Float16 support, while it may not be supported
by the i386 target (if it does not have SSE2).

While here, rename COMPILERT_RT_HAS_FLOAT16 to CRT_HAS_FLOAT16, to
conform more to the naming style used in int_lib.h and int_types.h.

[dim]

Fix typo.

[tstellar]

Is this something we need in the release branch?

[dim]

In D130718#3685679, @tstellar wrote:

Is this something we need in the release branch?

Yes please, provided that it's acceptable to everybody of course. I ran into this while building release/15.x after I had updated my host compiler to a very recent main snapshot (llvmorg-15-init-17485-ga3e38b4a206b). E.g. building release/15.x or recent main with clang 14.0.5 will work just fine, because it didn't yet support _Float16. But after rG655ba9c8a1d22075443711cc749f0b032e07adee landed, of course it did start supporting _Float16.

[pengfei]

@kparzysz reminded me. This is not the right direction to solve the problem. The ABI of runtime libraries should be constant rather than changing with different features. Imagining a program may be built with or without SSE2 and linked with the same runtime. Another problem is compatibility with libgcc. Using uint16_t is not compatible with libgcc anymore.

Fortunately, LLVM codegen (unfortunately Darwin isn't) was using __gnu_h2f_ieee/__gnu_f2h_ieee before the change https://godbolt.org/z/GnrT5vGr1. So an easy way to solve the problem is always assign -msse2 when build extendhftf2/trunctfhf2.

I have a patch D128872 for Darwin targets, I hope we can put it into the 15.x release.

[pengfei]

Or we simply refuse to build them if COMPILER_RT_HAS_FLOAT16 is not set.

[MaskRay]

LGTM. But I hope that others can check their builds.

[dim]

In D130718#3686439, @pengfei wrote:

@kparzysz reminded me. This is not the right direction to solve the problem. The ABI of runtime libraries should be constant rather than changing with different features. Imagining a program may be built with or without SSE2 and linked with the same runtime. Another problem is compatibility with libgcc. Using uint16_t is not compatible with libgcc anymore.

Fortunately, LLVM codegen (unfortunately Darwin isn't) was using __gnu_h2f_ieee/__gnu_f2h_ieee before the change https://godbolt.org/z/GnrT5vGr1. So an easy way to solve the problem is always assign -msse2 when build extendhftf2/trunctfhf2.

I have a patch D128872 for Darwin targets, I hope we can put it into the 15.x release.

If this is the case, then maybe the whole commit that introduced the use of _Float16 (i.e. rG655ba9c8a1d22075443711cc749f0b032e07adee) should be reverted *again*? (It's already titled 'Reland "Reland "Reland "Reland "[X86][RFC] Enable _Float16 type support on X86 following the psABI""""', so relanding it One More Time shouldn't be that difficult ;))

That said, rG655ba9c8a1d22075443711cc749f0b032e07adee's description also says "following the psABI" so maybe this is actually going to improve ABI compatibility?

[fmayer]

I think this broke the sanitizer-windows buildbot: https://lab.llvm.org/buildbot/#/builders/127/builds/33583/steps/4/logs/stdio

[99/120] Running the Builtins tests
-- Testing: 214 tests, 16 workers --
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60..
FAIL: Builtins-x86_64-windows :: truncdfhf2_test.c (53 of 214)
******************** TEST 'Builtins-x86_64-windows :: truncdfhf2_test.c' FAILED ********************
Script:
--
: 'RUN: at line 1';       C:/b/slave/sanitizer-windows/build/stage1/./bin/clang.exe   -gline-tables-only -gcodeview -gcolumn-info     -fno-builtin -I C:/b/slave/sanitizer-windows/llvm-project/compiler-rt\lib\builtins -nodefaultlibs C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\builtins\Unit\truncdfhf2_test.c C:/b/slave/sanitizer-windows/build/stage1/./lib/clang/16.0.0/lib/windows\clang_rt.builtins-x86_64.lib -o C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncdfhf2_test.c.tmp &&  C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncdfhf2_test.c.tmp
--
Exit Code: 1
Command Output (stdout):
--
$ ":" "RUN: at line 1"
$ "C:/b/slave/sanitizer-windows/build/stage1/./bin/clang.exe" "-gline-tables-only" "-gcodeview" "-gcolumn-info" "-fno-builtin" "-I" "C:/b/slave/sanitizer-windows/llvm-project/compiler-rt\lib\builtins" "-nodefaultlibs" "C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\builtins\Unit\truncdfhf2_test.c" "C:/b/slave/sanitizer-windows/build/stage1/./lib/clang/16.0.0/lib/windows\clang_rt.builtins-x86_64.lib" "-o" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncdfhf2_test.c.tmp"
$ "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncdfhf2_test.c.tmp"
# command output:
error in test__truncdfhf2(nan) = 0000, expected 0x7e00
error: command failed with exit status: 1
--
********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90.
FAIL: Builtins-x86_64-windows :: truncsfhf2_test.c (212 of 214)
******************** TEST 'Builtins-x86_64-windows :: truncsfhf2_test.c' FAILED ********************
Script:
--
: 'RUN: at line 1';       C:/b/slave/sanitizer-windows/build/stage1/./bin/clang.exe   -gline-tables-only -gcodeview -gcolumn-info     -fno-builtin -I C:/b/slave/sanitizer-windows/llvm-project/compiler-rt\lib\builtins -nodefaultlibs C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\builtins\Unit\truncsfhf2_test.c C:/b/slave/sanitizer-windows/build/stage1/./lib/clang/16.0.0/lib/windows\clang_rt.builtins-x86_64.lib -o C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncsfhf2_test.c.tmp &&  C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncsfhf2_test.c.tmp
--
Exit Code: 1
Command Output (stdout):
--
$ ":" "RUN: at line 1"
$ "C:/b/slave/sanitizer-windows/build/stage1/./bin/clang.exe" "-gline-tables-only" "-gcodeview" "-gcolumn-info" "-fno-builtin" "-I" "C:/b/slave/sanitizer-windows/llvm-project/compiler-rt\lib\builtins" "-nodefaultlibs" "C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\builtins\Unit\truncsfhf2_test.c" "C:/b/slave/sanitizer-windows/build/stage1/./lib/clang/16.0.0/lib/windows\clang_rt.builtins-x86_64.lib" "-o" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncsfhf2_test.c.tmp"
$ "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncsfhf2_test.c.tmp"
# command output:
error in test__truncsfhf2(nan) = 0000, expected 0x7e00
error: command failed with exit status: 1
--

[pengfei]

In D130718#3688103, @dim wrote:

In D130718#3686439, @pengfei wrote:

@kparzysz reminded me. This is not the right direction to solve the problem. The ABI of runtime libraries should be constant rather than changing with different features. Imagining a program may be built with or without SSE2 and linked with the same runtime. Another problem is compatibility with libgcc. Using uint16_t is not compatible with libgcc anymore.

Fortunately, LLVM codegen (unfortunately Darwin isn't) was using __gnu_h2f_ieee/__gnu_f2h_ieee before the change https://godbolt.org/z/GnrT5vGr1. So an easy way to solve the problem is always assign -msse2 when build extendhftf2/trunctfhf2.

I have a patch D128872 for Darwin targets, I hope we can put it into the 15.x release.

If this is the case, then maybe the whole commit that introduced the use of _Float16 (i.e. rG655ba9c8a1d22075443711cc749f0b032e07adee) should be reverted *again*? (It's already titled 'Reland "Reland "Reland "Reland "[X86][RFC] Enable _Float16 type support on X86 following the psABI""""', so relanding it One More Time shouldn't be that difficult ;))

It is nonsense to take the revert times as a reason.

That said, rG655ba9c8a1d22075443711cc749f0b032e07adee's description also says "following the psABI" so maybe this is actually going to improve ABI compatibility?

The psABI refers in particular to https://gitlab.com/x86-psABIs. There're some instruction limitations to make us only support _Float16 for SSE2 and up, see the discussion https://groups.google.com/g/llvm-dev/c/k5WLPVGSeWU. And if you disable SSE2, you will get error on GCC too https://godbolt.org/z/33v7r9noP.

That said, build and provide the FP16 runtime without SSE2 is out of the scope of psABI. As for a general ABI compatibility, e.g., keeping the same calling conversion as pre rG655ba9c in cases without SSE2, this patch also doesn't help much, because for them we use __gnu_h2f_ieee/__gnu_f2h_ieee rather than extendhftf2/trunctfhf2 (except for Darwin).

[pengfei]

In D130718#3688602, @fmayer wrote:

I think this broke the sanitizer-windows buildbot: https://lab.llvm.org/buildbot/#/builders/127/builds/33583/steps/4/logs/stdio

[99/120] Running the Builtins tests
-- Testing: 214 tests, 16 workers --
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60..
FAIL: Builtins-x86_64-windows :: truncdfhf2_test.c (53 of 214)
******************** TEST 'Builtins-x86_64-windows :: truncdfhf2_test.c' FAILED ********************
Script:
--
: 'RUN: at line 1';       C:/b/slave/sanitizer-windows/build/stage1/./bin/clang.exe   -gline-tables-only -gcodeview -gcolumn-info     -fno-builtin -I C:/b/slave/sanitizer-windows/llvm-project/compiler-rt\lib\builtins -nodefaultlibs C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\builtins\Unit\truncdfhf2_test.c C:/b/slave/sanitizer-windows/build/stage1/./lib/clang/16.0.0/lib/windows\clang_rt.builtins-x86_64.lib -o C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncdfhf2_test.c.tmp &&  C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncdfhf2_test.c.tmp
--
Exit Code: 1
Command Output (stdout):
--
$ ":" "RUN: at line 1"
$ "C:/b/slave/sanitizer-windows/build/stage1/./bin/clang.exe" "-gline-tables-only" "-gcodeview" "-gcolumn-info" "-fno-builtin" "-I" "C:/b/slave/sanitizer-windows/llvm-project/compiler-rt\lib\builtins" "-nodefaultlibs" "C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\builtins\Unit\truncdfhf2_test.c" "C:/b/slave/sanitizer-windows/build/stage1/./lib/clang/16.0.0/lib/windows\clang_rt.builtins-x86_64.lib" "-o" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncdfhf2_test.c.tmp"
$ "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncdfhf2_test.c.tmp"
# command output:
error in test__truncdfhf2(nan) = 0000, expected 0x7e00
error: command failed with exit status: 1
--
********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90.
FAIL: Builtins-x86_64-windows :: truncsfhf2_test.c (212 of 214)
******************** TEST 'Builtins-x86_64-windows :: truncsfhf2_test.c' FAILED ********************
Script:
--
: 'RUN: at line 1';       C:/b/slave/sanitizer-windows/build/stage1/./bin/clang.exe   -gline-tables-only -gcodeview -gcolumn-info     -fno-builtin -I C:/b/slave/sanitizer-windows/llvm-project/compiler-rt\lib\builtins -nodefaultlibs C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\builtins\Unit\truncsfhf2_test.c C:/b/slave/sanitizer-windows/build/stage1/./lib/clang/16.0.0/lib/windows\clang_rt.builtins-x86_64.lib -o C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncsfhf2_test.c.tmp &&  C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncsfhf2_test.c.tmp
--
Exit Code: 1
Command Output (stdout):
--
$ ":" "RUN: at line 1"
$ "C:/b/slave/sanitizer-windows/build/stage1/./bin/clang.exe" "-gline-tables-only" "-gcodeview" "-gcolumn-info" "-fno-builtin" "-I" "C:/b/slave/sanitizer-windows/llvm-project/compiler-rt\lib\builtins" "-nodefaultlibs" "C:\b\slave\sanitizer-windows\llvm-project\compiler-rt\test\builtins\Unit\truncsfhf2_test.c" "C:/b/slave/sanitizer-windows/build/stage1/./lib/clang/16.0.0/lib/windows\clang_rt.builtins-x86_64.lib" "-o" "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncsfhf2_test.c.tmp"
$ "C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\builtins\Unit\X86_64WindowsConfig\Output\truncsfhf2_test.c.tmp"
# command output:
error in test__truncsfhf2(nan) = 0000, expected 0x7e00
error: command failed with exit status: 1
--

Thanks for the reporting. Reverted.

[dim]

Okay, so do we continue with this approach at all, then? The problem that x86_64 builds fail by default on non-gcc compilers still stands. I'm just not good enough in handling the CMake logic to figure that out, if we have to handle it via CMake.

[pengfei]

Neither do I. The compiler-rt files and the CMake is a maze to me. For example, we have truncsfhf2.c/extendhfsf2.c;trunctfhf2.c/extendhftf2.c;truncdfhf2.c in compiler-rt, but we are missing __extendhfdf2, __truncxfhf2/__extendhfxf2 compared to gcc. Besides, truncsfhf2.c/extendhfsf2.c/truncdfhf2.c use src_t/dst_t rather than _Float16 used in trunctfhf2.c/extendhftf2.c. I wonder if you can solve your problem by just replacing _Float16 by src_t/dst_t. However, it cannot explain why the buildbot failed only in truncsfhf2_test.c/truncdfhf2_test.c while passed in extendhfsf2_test.c ...

From the view point of a general solution, I think we can add -msse2 for X86 in the CMake. I think forcing it is not a problem given GCC has already implies it as you observed. OTOH, when you using configuration generated for x86_64 for i386 targets, you have acquiesced SSE2 is usable on i386. Otherwise, it is misuse in such scenario.

[jwakely]

In D130718#3688875, @dim wrote:

The problem that x86_64 builds fail by default on non-gcc compilers still stands.

It fails for GCC too. cc -m32 does not set -msse2 by default in vanilla GCC, see https://discourse.llvm.org/t/how-to-build-compiler-rt-for-new-x86-half-float-abi/63366/20?u=jwakely

[pengfei]

In D130718#3826529, @jwakely wrote:

In D130718#3688875, @dim wrote:

The problem that x86_64 builds fail by default on non-gcc compilers still stands.

It fails for GCC too. cc -m32 does not set -msse2 by default in vanilla GCC, see https://discourse.llvm.org/t/how-to-build-compiler-rt-for-new-x86-half-float-abi/63366/20?u=jwakely

Thanks for the information! Then I believe the right way is to always pass -m32 -msse2 together when using the type.

[vitalybuka]

What do we need to move forward with the patch?

HEAD as-is is broken on Ubuntu 22.10
https://lab.llvm.org/buildbot/#/builders/169/builds/13450/steps/7/logs/stdio

[pengfei]

In D130718#3916720, @vitalybuka wrote:

What do we need to move forward with the patch?

HEAD as-is is broken on Ubuntu 22.10
https://lab.llvm.org/buildbot/#/builders/169/builds/13450/steps/7/logs/stdio

I noticed the bot is starting to fail 3 days ago, but the patch merged for months. Is there any recent change exposed the problem?

As disscussed in https://discourse.llvm.org/t/how-to-build-compiler-rt-for-new-x86-half-float-abi/63366/25 the build of 32-bits using 64-bit config is the root cause. I think always turning on SSE2 explicitly in the 64-bit config should be a feasible workaround.

[dim]

In D130718#3916780, @pengfei wrote:

In D130718#3916720, @vitalybuka wrote:

What do we need to move forward with the patch?

HEAD as-is is broken on Ubuntu 22.10
https://lab.llvm.org/buildbot/#/builders/169/builds/13450/steps/7/logs/stdio

I noticed the bot is starting to fail 3 days ago, but the patch merged for months. Is there any recent change exposed the problem?

As disscussed in https://discourse.llvm.org/t/how-to-build-compiler-rt-for-new-x86-half-float-abi/63366/25 the build of 32-bits using 64-bit config is the root cause. I think always turning on SSE2 explicitly in the 64-bit config should be a feasible workaround.

I have another patch coming up, which I have been using for the 15.0.x test builds.

[vitalybuka]

In D130718#3916780, @pengfei wrote:

In D130718#3916720, @vitalybuka wrote:

What do we need to move forward with the patch?

HEAD as-is is broken on Ubuntu 22.10
https://lab.llvm.org/buildbot/#/builders/169/builds/13450/steps/7/logs/stdio

I noticed the bot is starting to fail 3 days ago, but the patch merged for months. Is there any recent change exposed the problem?

3 days was caused by unrelated reasons, which I fixed already.
yesterday I tried to update the bot from 22.04 ( with clang 14....) -> 22.10 ( with clang 15.0.4). I reverted it back to 22.04, but would like to upgrade it later again.

[pengfei]

In D130718#3918705, @vitalybuka wrote:

In D130718#3916780, @pengfei wrote:

In D130718#3916720, @vitalybuka wrote:

What do we need to move forward with the patch?

HEAD as-is is broken on Ubuntu 22.10
https://lab.llvm.org/buildbot/#/builders/169/builds/13450/steps/7/logs/stdio

I noticed the bot is starting to fail 3 days ago, but the patch merged for months. Is there any recent change exposed the problem?

3 days was caused by unrelated reasons, which I fixed already.
yesterday I tried to update the bot from 22.04 ( with clang 14....) -> 22.10 ( with clang 15.0.4). I reverted it back to 22.04, but would like to upgrade it later again.

I see, thanks for the information.

[dim]

Abandoning in favor of D136044.

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

 builtin_check_c_compiler_source(COMPILER_RT_HAS_ATOMIC_KEYWORD
 "
 int foo(int x, int y) {
  _Atomic int result = x * y;
  return result;
 }
 ")
 
-builtin_check_c_compiler_source(COMPILER_RT_HAS_FLOAT16
-"
-_Float16 foo(_Float16 x) {
- return x;
-}
-"
-)
-
 builtin_check_c_compiler_source(COMPILER_RT_HAS_ASM_LSE
 "
 asm(\".arch armv8-a+lse\");
 asm(\"cas w0, w1, [x2]\");
 ")
 
 set(ARM64 aarch64)
 set(ARM32 arm armhf armv6m armv7m armv7em armv7 armv7s armv7k armv8m.main armv8.1m.main)

compiler-rt/lib/builtins/CMakeLists.txt

if (APPLE)
   darwin_add_builtin_libraries(${BUILTIN_SUPPORTED_OS})
 else ()
   set(BUILTIN_CFLAGS "")
 
   if (COMPILER_RT_HAS_FCF_PROTECTION_FLAG)
     append_list_if(COMPILER_RT_ENABLE_CET -fcf-protection=full BUILTIN_CFLAGS)
   endif()
 
-  append_list_if(COMPILER_RT_HAS_FLOAT16 -DCOMPILER_RT_HAS_FLOAT16 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
   # cmake step. Add them manually if this is a standalone build.
   if(COMPILER_RT_STANDALONE_BUILD)
     if(COMPILER_RT_BUILTINS_ENABLE_PIC)
       append_list_if(COMPILER_RT_HAS_FPIC_FLAG -fPIC BUILTIN_CFLAGS)
     endif()

compiler-rt/lib/builtins/extendhftf2.c

 //===-- lib/extendhftf2.c - half -> quad conversion ---------------*- C -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
 #if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT) &&                     \
-    defined(COMPILER_RT_HAS_FLOAT16)
+    defined(CRT_HAS_FLOAT16)
 #define SRC_HALF
 #define DST_QUAD
 #include "fp_extend_impl.inc"
 
 COMPILER_RT_ABI long double __extendhftf2(_Float16 a) {
   return __extendXfYf2__(a);
 }
 
 #endif

compiler-rt/lib/builtins/fp_extend.h

#else
   if (a & REP_C(0xffffffff00000000))
     return clzsi(a >> 32);
   else
     return 32 + clzsi(a & REP_C(0xffffffff));
 #endif
 }
 
 #elif defined SRC_HALF
-#ifdef COMPILER_RT_HAS_FLOAT16
+#ifdef CRT_HAS_FLOAT16
 typedef _Float16 src_t;
 #else
 typedef uint16_t src_t;
 #endif
 typedef uint16_t src_rep_t;
 #define SRC_REP_C UINT16_C
 static const int srcSigBits = 10;
 #define src_rep_t_clz __builtin_clz

compiler-rt/lib/builtins/fp_trunc.h

 
 #elif defined DST_SINGLE
 typedef float dst_t;
 typedef uint32_t dst_rep_t;
 #define DST_REP_C UINT32_C
 static const int dstSigBits = 23;
 
 #elif defined DST_HALF
-#ifdef COMPILER_RT_HAS_FLOAT16
+#ifdef CRT_HAS_FLOAT16
 typedef _Float16 dst_t;
 #else
 typedef uint16_t dst_t;
 #endif
 typedef uint16_t dst_rep_t;
 #define DST_REP_C UINT16_C
 static const int dstSigBits = 10;
 

compiler-rt/lib/builtins/int_types.h

#if (defined(__i386__) || defined(__x86_64__)) &&                              \
     !(defined(_MSC_VER) || defined(__ANDROID__))
 #define HAS_80_BIT_LONG_DOUBLE 1
 #elif defined(__m68k__) || defined(__ia64__)
 #define HAS_80_BIT_LONG_DOUBLE 1
 #else
 #define HAS_80_BIT_LONG_DOUBLE 0
 #endif
 
+#ifdef __FLT16_MAX__
+#define CRT_HAS_FLOAT16
+#endif
+
 #if CRT_HAS_FLOATING_POINT
 typedef union {
   uqwords u;
   long double f;
 } long_double_bits;
 
 #if __STDC_VERSION__ >= 199901L
 typedef float _Complex Fcomplex;

compiler-rt/lib/builtins/trunctfhf2.c

 //===-- lib/trunctfhf2.c - quad -> half conversion ----------------*- C -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
 #if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT) &&                     \
-    defined(COMPILER_RT_HAS_FLOAT16)
+    defined(CRT_HAS_FLOAT16)
 #define SRC_QUAD
 #define DST_HALF
 #include "fp_trunc_impl.inc"
 
 COMPILER_RT_ABI _Float16 __trunctfhf2(long double a) {
   return __truncXfYf2__(a);
 }
 
 #endif

compiler-rt/test/builtins/CMakeLists.txt

if (${arch} STREQUAL "armhf")
     string(REPLACE ";" " " BUILTINS_TEST_TARGET_CFLAGS "${BUILTINS_TEST_TARGET_CFLAGS}")
   endif()
 
   if (${arch} STREQUAL "riscv32")
     list(APPEND BUILTINS_TEST_TARGET_CFLAGS -fforce-enable-int128)
     string(REPLACE ";" " " BUILTINS_TEST_TARGET_CFLAGS "${BUILTINS_TEST_TARGET_CFLAGS}")
   endif()
 
-  if(APPLE)
-    # TODO: Support the new ABI on Apple platforms.
-    if (${arch} MATCHES "arm|aarch64|arm64" AND COMPILER_RT_HAS_FLOAT16)
-      list(APPEND BUILTINS_TEST_TARGET_CFLAGS -DCOMPILER_RT_HAS_FLOAT16)
-      string(REPLACE ";" " " BUILTINS_TEST_TARGET_CFLAGS "${BUILTINS_TEST_TARGET_CFLAGS}")
-    endif()
-  else()
-    if (${arch} MATCHES "arm|aarch64|arm64|i?86|x86_64|AMD64|riscv32|riscv64" AND COMPILER_RT_HAS_FLOAT16)
-      list(APPEND BUILTINS_TEST_TARGET_CFLAGS -DCOMPILER_RT_HAS_FLOAT16)
-      string(REPLACE ";" " " BUILTINS_TEST_TARGET_CFLAGS "${BUILTINS_TEST_TARGET_CFLAGS}")
-    endif()
-  endif()
-
   if(COMPILER_RT_ENABLE_CET)
     if(NOT arch MATCHES "i?86|x86_64|AMD64")
       message(SEND_ERROR "${arch} does not support CET")
     endif()
     if(COMPILER_RT_HAS_FCF_PROTECTION_FLAG)
       list(APPEND BUILTINS_TEST_TARGET_CFLAGS -fcf-protection=full)
       string(REPLACE ";" " " BUILTINS_TEST_TARGET_CFLAGS "${BUILTINS_TEST_TARGET_CFLAGS}")
     endif()

compiler-rt/test/builtins/Unit/extendhftf2_test.c

 // RUN: %clang_builtins %s %librt -o %t && %run %t
 // REQUIRES: librt_has_extendhftf2
 
 #include "int_lib.h"
 #include <stdio.h>
 
-#if __LDBL_MANT_DIG__ == 113 && defined(COMPILER_RT_HAS_FLOAT16)
+#if __LDBL_MANT_DIG__ == 113 && defined(CRT_HAS_FLOAT16)
 
 #include "fp_test.h"
 
 COMPILER_RT_ABI long double __extendhftf2(TYPE_FP16 a);
 
 int test__extendhftf2(TYPE_FP16 a, uint64_t expectedHi, uint64_t expectedLo) {
   long double x = __extendhftf2(a);
   int ret = compareResultLD(x, expectedHi, expectedLo);
 
   if (ret) {
     printf("error in test__extendhftf2(%#.4x) = %.20Lf, "
            "expected %.20Lf\n",
            toRep16(a), x,
            fromRep128(expectedHi, expectedLo));
   }
   return ret;
 }
 
 char assumption_1[sizeof(TYPE_FP16) * CHAR_BIT == 16] = {0};
 
 #endif
 
 int main() {
-#if __LDBL_MANT_DIG__ == 113 && defined(COMPILER_RT_HAS_FLOAT16)
+#if __LDBL_MANT_DIG__ == 113 && defined(CRT_HAS_FLOAT16)
   // qNaN
   if (test__extendhftf2(makeQNaN16(),
                         UINT64_C(0x7fff800000000000),
                         UINT64_C(0x0)))
     return 1;
   // NaN
   if (test__extendhftf2(makeNaN16(UINT16_C(0x0100)),
                         UINT64_C(0x7fff400000000000),

compiler-rt/test/builtins/Unit/fp_test.h

-#include <stdlib.h>
+#include "int_lib.h"
 #include <limits.h>
-#include <string.h>
 #include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
 
-#ifdef COMPILER_RT_HAS_FLOAT16
-#define TYPE_FP16 _Float16
+#ifdef CRT_HAS_FLOAT16
+#  define TYPE_FP16 _Float16
 #else
 #define TYPE_FP16 uint16_t
 #endif
 
 enum EXPECTED_RESULT {
     LESS_0, LESS_EQUAL_0, EQUAL_0, GREATER_0, GREATER_EQUAL_0, NEQUAL_0
 };
 
 static inline TYPE_FP16 fromRep16(uint16_t x)
 {
-#ifdef COMPILER_RT_HAS_FLOAT16
-    TYPE_FP16 ret;
-    memcpy(&ret, &x, sizeof(ret));
-    return ret;
+#ifdef CRT_HAS_FLOAT16
 #else
     return x;
 #endif
 }
 
 static inline float fromRep32(uint32_t x)
 {
     float ret;
static inline long double fromRep128(uint64_t hi, uint64_t lo)
     long double ret;
     memcpy(&ret, &x, 16);
     return ret;
 }
 #endif
 
 static inline uint16_t toRep16(TYPE_FP16 x)
 {
-#ifdef COMPILER_RT_HAS_FLOAT16
+#ifdef CRT_HAS_FLOAT16
     uint16_t ret;
     memcpy(&ret, &x, sizeof(ret));
     return ret;
 #else
     return x;
 #endif
 }
 

compiler-rt/test/builtins/Unit/trunctfhf2_test.c

 // RUN: %clang_builtins %s %librt -o %t && %run %t
 // REQUIRES: librt_has_trunctfhf2
 
 #include "int_lib.h"
 #include <stdio.h>
 
-#if __LDBL_MANT_DIG__ == 113 && defined(COMPILER_RT_HAS_FLOAT16)
+#if __LDBL_MANT_DIG__ == 113 && defined(CRT_HAS_FLOAT16)
 
 #include "fp_test.h"
 
 TYPE_FP16 __trunctfhf2(long double a);
 
 int test__trunctfhf2(long double a, uint16_t expected) {
   TYPE_FP16 x = __trunctfhf2(a);
   int ret = compareResultH(x, expected);
 
   if (ret) {
     printf("error in test__trunctfhf2(%.20Lf) = %#.4x, "
            "expected %#.4x\n",
            a, toRep16(x), expected);
   }
   return ret;
 }
 
 char assumption_1[sizeof(TYPE_FP16) * CHAR_BIT == 16] = {0};
 
 #endif
 
 int main() {
-#if __LDBL_MANT_DIG__ == 113 && defined(COMPILER_RT_HAS_FLOAT16)
+#if __LDBL_MANT_DIG__ == 113 && defined(CRT_HAS_FLOAT16)
   // qNaN
   if (test__trunctfhf2(makeQNaN128(),
                        UINT16_C(0x7e00)))
     return 1;
   // NaN
   if (test__trunctfhf2(makeNaN128(UINT64_C(0x810000000000)),
                        UINT16_C(0x7e00)))
     return 1;