[libc] add shared subtf3 builtin

[hulxv]

Re-exposes LLVM-libc's __subtf3 as shared::subtf3 for reuse by compiler-rt's builtins.

Stacked change - merge these first:

• [libc] introduce shared compiler-rt builtins #200094

Part of #197824

[llvmorg-github-actions]

@llvm/pr-subscribers-libc

Author: hulxv (hulxv)

Changes

Re-exposes LLVM-libc's __subtf3 as shared::subtf3 for reuse by compiler-rt's builtins.

Stacked change - merge these first:

• #200094

---

Full diff: https://github.com/llvm/llvm-project/pull/205669.diff

11 Files Affected:

• (modified) libc/include/llvm-libc-macros/float-macros.h (+6)
• (added) libc/shared/builtins.h (+23)
• (added) libc/shared/builtins/addtf3.h (+35)
• (added) libc/shared/builtins/subtf3.h (+35)
• (modified) libc/src/__support/CMakeLists.txt (+1)
• (modified) libc/src/__support/FPUtil/dyadic_float.h (+3)
• (added) libc/src/__support/builtins/CMakeLists.txt (+19)
• (added) libc/src/__support/builtins/addtf3.h (+38)
• (added) libc/src/__support/builtins/subtf3.h (+38)
• (modified) libc/test/shared/CMakeLists.txt (+10)
• (added) libc/test/shared/shared_builtins_test.cpp (+39)

diff --git a/libc/include/llvm-libc-macros/float-macros.h b/libc/include/llvm-libc-macros/float-macros.h
index a25ef60a293d3..38a3a771cca54 100644
--- a/libc/include/llvm-libc-macros/float-macros.h
+++ b/libc/include/llvm-libc-macros/float-macros.h
@@ -9,6 +9,12 @@
 #ifndef LLVM_LIBC_MACROS_FLOAT_MACROS_H
 #define LLVM_LIBC_MACROS_FLOAT_MACROS_H
 
+// __has_builtin is a Clang extension; GCC < 10 doesn't define it, which
+// turns a bare `#if __has_builtin(...)` into a preprocessor syntax error.
+#ifndef __has_builtin
+#define __has_builtin(x) 0
+#endif
+
 #ifndef FLT_RADIX
 #define FLT_RADIX __FLT_RADIX__
 #endif // FLT_RADIX
diff --git a/libc/shared/builtins.h b/libc/shared/builtins.h
new file mode 100644
index 0000000000000..0bb156131423d
--- /dev/null
+++ b/libc/shared/builtins.h
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This header aggregates LLVM-libc's shared compiler-rt builtins so that
+/// they can be reused by compiler-rt's builtins.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SHARED_BUILTINS_H
+#define LLVM_LIBC_SHARED_BUILTINS_H
+
+#include "libc_common.h"
+
+#include "builtins/addtf3.h"
+#include "builtins/subtf3.h"
+
+#endif // LLVM_LIBC_SHARED_BUILTINS_H
diff --git a/libc/shared/builtins/addtf3.h b/libc/shared/builtins/addtf3.h
new file mode 100644
index 0000000000000..33534beeb91c7
--- /dev/null
+++ b/libc/shared/builtins/addtf3.h
@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This header exposes LLVM-libc's __addtf3 implementation as shared::addtf3
+/// so that it can be reused by compiler-rt's builtins.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SHARED_BUILTINS_ADDTF3_H
+#define LLVM_LIBC_SHARED_BUILTINS_ADDTF3_H
+
+#include "include/llvm-libc-types/float128.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT128
+
+#include "shared/libc_common.h"
+#include "src/__support/builtins/addtf3.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using builtins::addtf3;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT128
+
+#endif // LLVM_LIBC_SHARED_BUILTINS_ADDTF3_H
diff --git a/libc/shared/builtins/subtf3.h b/libc/shared/builtins/subtf3.h
new file mode 100644
index 0000000000000..a7cecef8b0479
--- /dev/null
+++ b/libc/shared/builtins/subtf3.h
@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This header exposes LLVM-libc's __subtf3 implementation as shared::subtf3 so
+/// that it can be reused by compiler-rt's builtins.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SHARED_BUILTINS_SUBTF3_H
+#define LLVM_LIBC_SHARED_BUILTINS_SUBTF3_H
+
+#include "include/llvm-libc-types/float128.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT128
+
+#include "shared/libc_common.h"
+#include "src/__support/builtins/subtf3.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using builtins::subtf3;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT128
+
+#endif // LLVM_LIBC_SHARED_BUILTINS_SUBTF3_H
diff --git a/libc/src/__support/CMakeLists.txt b/libc/src/__support/CMakeLists.txt
index 9d08b4bcf7303..c09ca012c3594 100644
--- a/libc/src/__support/CMakeLists.txt
+++ b/libc/src/__support/CMakeLists.txt
@@ -472,6 +472,7 @@ add_subdirectory(wchar)
 add_subdirectory(wctype)
 
 add_subdirectory(math)
+add_subdirectory(builtins)
 if(LIBC_COMPILER_HAS_EXT_VECTOR_TYPE)
   add_subdirectory(mathvec)
 endif()
diff --git a/libc/src/__support/FPUtil/dyadic_float.h b/libc/src/__support/FPUtil/dyadic_float.h
index 7e4ea2f1a81be..d99a14f35f38e 100644
--- a/libc/src/__support/FPUtil/dyadic_float.h
+++ b/libc/src/__support/FPUtil/dyadic_float.h
@@ -415,6 +415,9 @@ template <size_t Bits> struct DyadicFloat {
     if constexpr (cpp::is_same_v<T, bfloat16>
 #if defined(LIBC_TYPES_HAS_FLOAT16) && !defined(__LIBC_USE_FLOAT16_CONVERSION)
                   || cpp::is_same_v<T, float16>
+#endif
+#if defined(LIBC_TYPES_HAS_FLOAT128)
+                  || cpp::is_same_v<T, float128>
 #endif
     )
       return generic_as<T, ShouldSignalExceptions>();
diff --git a/libc/src/__support/builtins/CMakeLists.txt b/libc/src/__support/builtins/CMakeLists.txt
new file mode 100644
index 0000000000000..d3d1d65babce8
--- /dev/null
+++ b/libc/src/__support/builtins/CMakeLists.txt
@@ -0,0 +1,19 @@
+add_header_library(
+  addtf3
+  HDRS
+    addtf3.h
+  DEPENDS
+    libc.include.llvm-libc-types.float128
+    libc.src.__support.FPUtil.generic.add_sub
+    libc.src.__support.macros.config
+)
+
+add_header_library(
+  subtf3
+  HDRS
+    subtf3.h
+  DEPENDS
+    libc.include.llvm-libc-types.float128
+    libc.src.__support.FPUtil.generic.add_sub
+    libc.src.__support.macros.config
+)
diff --git a/libc/src/__support/builtins/addtf3.h b/libc/src/__support/builtins/addtf3.h
new file mode 100644
index 0000000000000..f33036f53ec30
--- /dev/null
+++ b/libc/src/__support/builtins/addtf3.h
@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This header exposes LLVM-libc's __addtf3 implementation as
+/// builtins::addtf3 so that it can be reused by compiler-rt's builtins.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_BUILTINS_ADDTF3_H
+#define LLVM_LIBC_SRC___SUPPORT_BUILTINS_ADDTF3_H
+
+#include "include/llvm-libc-types/float128.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT128
+
+#include "src/__support/FPUtil/generic/add_sub.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace builtins {
+
+// Mirrors the compiler-rt __addtf3 ABI: a + b at float128 precision.
+LIBC_INLINE float128 addtf3(float128 x, float128 y) {
+  return fputil::generic::add<float128>(x, y);
+}
+
+} // namespace builtins
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT128
+
+#endif // LLVM_LIBC_SRC___SUPPORT_BUILTINS_ADDTF3_H
diff --git a/libc/src/__support/builtins/subtf3.h b/libc/src/__support/builtins/subtf3.h
new file mode 100644
index 0000000000000..bd758cce0f5f6
--- /dev/null
+++ b/libc/src/__support/builtins/subtf3.h
@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This header exposes LLVM-libc's __subtf3 implementation as builtins::subtf3
+/// so that it can be reused by compiler-rt's builtins.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_BUILTINS_SUBTF3_H
+#define LLVM_LIBC_SRC___SUPPORT_BUILTINS_SUBTF3_H
+
+#include "include/llvm-libc-types/float128.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT128
+
+#include "src/__support/FPUtil/generic/add_sub.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace builtins {
+
+// Subtraction at float128 precision; mirrors compiler-rt's __subtf3.
+LIBC_INLINE float128 subtf3(float128 x, float128 y) {
+  return fputil::generic::sub<float128>(x, y);
+}
+
+} // namespace builtins
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT128
+
+#endif // LLVM_LIBC_SRC___SUPPORT_BUILTINS_SUBTF3_H
diff --git a/libc/test/shared/CMakeLists.txt b/libc/test/shared/CMakeLists.txt
index 7a5c3a369c2fc..0f8027e2e0057 100644
--- a/libc/test/shared/CMakeLists.txt
+++ b/libc/test/shared/CMakeLists.txt
@@ -814,6 +814,16 @@ add_fp_unittest(
 )
 endif() # LIBC_TEST_SKIP_SHARED_MATH_TESTS
 
+add_fp_unittest(
+  shared_builtins_test
+  SUITE
+    libc-shared-tests
+  SRCS
+    shared_builtins_test.cpp
+  DEPENDS
+    libc.src.__support.builtins.addtf3
+)
+
 add_fp_unittest(
   shared_str_to_num_test
   SUITE
diff --git a/libc/test/shared/shared_builtins_test.cpp b/libc/test/shared/shared_builtins_test.cpp
new file mode 100644
index 0000000000000..d2d9c71d4f4fd
--- /dev/null
+++ b/libc/test/shared/shared_builtins_test.cpp
@@ -0,0 +1,39 @@
+//===-- Unittests for shared builtins -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "shared/builtins.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcSharedBuiltinsTest, AllFloat) {
+  // TODO: assertions for shared::*sf3 builtins.
+}
+
+TEST(LlvmLibcSharedBuiltinsTest, AllDouble) {
+  // TODO: assertions for shared::*df3 builtins.
+}
+
+#ifdef LIBC_TYPES_HAS_FLOAT128
+
+TEST(LlvmLibcSharedBuiltinsTest, AllFloat128) {
+  namespace shared = LIBC_NAMESPACE::shared;
+
+  EXPECT_FP_EQ(float128(3.0), shared::addtf3(float128(1.0), float128(2.0)));
+}
+
+#endif // LIBC_TYPES_HAS_FLOAT128
+
+#ifdef LIBC_TYPES_HAS_FLOAT128
+
+TEST(LlvmLibcSharedBuiltinsTest, Subtf3) {
+  namespace shared = LIBC_NAMESPACE::shared;
+
+  EXPECT_FP_EQ(float128(2.0), shared::subtf3(float128(5.0), float128(3.0)));
+}
+
+#endif // LIBC_TYPES_HAS_FLOAT128

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