[compiler-rt][builtins] introduce libc math routines

compiler-rt/lib/builtins/CMakeLists.txt

@@ -243,6 +243,30 @@ set(GENERIC_TF_SOURCES
   trunctfsf2.c
 )
 
+option(COMPILER_RT_USE_LIBC_MATH
+      "Use LLVM libc math routines for floating-point builtins" OFF)
+
+# Swap the legacy soft-float <name>.c builtin in <list> for the libc-backed
+# <name>.cpp implementation (which delegates to LIBC_NAMESPACE::shared::*).
+macro(use_libc_builtin list_var name)
+  list(REMOVE_ITEM ${list_var} ${name}.c)
+  list(APPEND ${list_var} ${name}.cpp)
+endmacro()
+
+if(COMPILER_RT_USE_LIBC_MATH)
+  include(FindLibcCommonUtils)
+  if(NOT TARGET llvm-libc-common-utilities)
+    message(FATAL_ERROR "LLVM libc is not found at ${libc_path}.")
+  endif()
+
+  get_target_property(_libc_include_dirs llvm-libc-common-utilities
+                      INTERFACE_INCLUDE_DIRECTORIES)
+  include_directories(SYSTEM ${_libc_include_dirs})
+  add_definitions(-DCOMPILER_RT_USE_LIBC_MATH)
+
+  use_libc_builtin(GENERIC_TF_SOURCES addtf3)
+endif()
+
 option(COMPILER_RT_EXCLUDE_ATOMIC_BUILTIN
   "Skip the atomic builtin (these should normally be provided by a shared library)"
   On)

compiler-rt/lib/builtins/addtf3.cpp

@@ -0,0 +1,22 @@
+//===-- lib/addtf3.cpp - Quad-precision addition (libc-backed) --*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// __addtf3 implemented on top of LLVM-libc's shared::addtf3 instruction.
+//
+//===----------------------------------------------------------------------===//
+
+#define QUAD_PRECISION
+#include "fp_lib.h"
+
+#include "fp_libc_config.h"
+#include "int_lib.h"
+#include "shared/builtins/addtf3.h"
+
+extern "C" COMPILER_RT_ABI fp_t __addtf3(fp_t a, fp_t b) {
+  return LIBC_NAMESPACE::shared::addtf3(a, b);
+}

compiler-rt/lib/builtins/fp_libc_config.h

@@ -0,0 +1,26 @@
+//===-- lib/fp_libc_config.h - LLVM-libc compile config --------*- C -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Compile-time configuration consumed by LLVM-libc's fputil headers when they
+// are included from compiler-rt builtins under COMPILER_RT_USE_LIBC_MATH.
+// Pins the libc namespace to __llvm_libc_rt to avoid clashing with libc's own
+// symbols, and disables errno / FP-exception bookkeeping inside libc routines
+// called from builtins.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FP_LIBC_CONFIG_H
+#define FP_LIBC_CONFIG_H
+
+#ifndef LIBC_NAMESPACE
+#define LIBC_NAMESPACE __llvm_libc_rt
+#endif
+
+#define LIBC_MATH (LIBC_MATH_NO_ERRNO | LIBC_MATH_NO_EXCEPT)
+
+#endif // FP_LIBC_CONFIG_H