[compiler-rt] compiler-rt: Fix cmake check for _Float16 and __bf16 (PR #83639)

[Khem Raj via llvm-commits]

https://github.com/kraj created https://github.com/llvm/llvm-project/pull/83639

When using check_c_source_compiles cmake function, main has to be provided, otherwise while compile step will be fine but linking step will fail as there will be no main function and test will fail and disable building HF builtins into compiler-rt

Fixes configure errors like below

aarch64-yoe-linux-ld.lld: error: undefined symbol: main
 referenced by start.S:81 (../sysdeps/aarch64/start.S:81)
               /mnt/b/yoe/master/build/tmp/work/cortexa72-cortexa53-crypto-yoe-linux/compiler-rt/18.1.0/recipe-sysroot/usr/lib/Scrt1.o:(_start)
 referenced by start.S:82 (../sysdeps/aarch64/start.S:82)
               /mnt/b/yoe/master/build/tmp/work/cortexa72-cortexa53-crypto-yoe-linux/compiler-rt/18.1.0/recipe-sysroot/usr/lib/Scrt1.o:(_start)
 aarch64-yoe-linux-clang: error: linker command failed with exit code 1 (use -v to see invocation)

>From 8e7a61220a1b0a5386872596f6c168f85215849e Mon Sep 17 00:00:00 2001
From: Khem Raj <raj.khem at gmail.com>
Date: Fri, 1 Mar 2024 16:47:46 -0800
Subject: [PATCH] compiler-rt: Fix cmake check for _Float16 and __bf16

When using check_c_source_compiles cmake function, main has to be
provided, otherwise while compile step will be fine but linking step
will fail as there will be no main function and test will fail and
disable building HF builtins into compiler-rt

Fixes configure errors like below

aarch64-yoe-linux-ld.lld: error: undefined symbol: main
 referenced by start.S:81 (../sysdeps/aarch64/start.S:81)
               /mnt/b/yoe/master/build/tmp/work/cortexa72-cortexa53-crypto-yoe-linux/compiler-rt/18.1.0/recipe-sysroot/usr/lib/Scrt1.o:(_start)
 referenced by start.S:82 (../sysdeps/aarch64/start.S:82)
               /mnt/b/yoe/master/build/tmp/work/cortexa72-cortexa53-crypto-yoe-linux/compiler-rt/18.1.0/recipe-sysroot/usr/lib/Scrt1.o:(_start)
 aarch64-yoe-linux-clang: error: linker command failed with exit code 1 (use -v to see invocation)

Signed-off-by: Khem Raj <raj.khem at gmail.com>
---
 compiler-rt/lib/builtins/CMakeLists.txt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/compiler-rt/lib/builtins/CMakeLists.txt b/compiler-rt/lib/builtins/CMakeLists.txt
index 83f7697a4a2b42..2e7ca0c3140752 100644
--- a/compiler-rt/lib/builtins/CMakeLists.txt
+++ b/compiler-rt/lib/builtins/CMakeLists.txt
@@ -828,10 +828,10 @@ else ()
           endif()
         endif()
       endif()
-      check_c_source_compiles("_Float16 foo(_Float16 x) { return x; }"
+      check_c_source_compiles("_Float16 foo(_Float16 x) { return x; } int main(void) { return foo(1.0); }"
                               COMPILER_RT_HAS_${arch}_FLOAT16)
       append_list_if(COMPILER_RT_HAS_${arch}_FLOAT16 -DCOMPILER_RT_HAS_FLOAT16 BUILTIN_CFLAGS_${arch})
-      check_c_source_compiles("__bf16 foo(__bf16 x) { return x; }"
+      check_c_source_compiles("__bf16 foo(__bf16 x) { return x; } int main(void) { return foo(1.0); }"
                               COMPILER_RT_HAS_${arch}_BFLOAT16)
       # Build BF16 files only when "__bf16" is available.
       if(COMPILER_RT_HAS_${arch}_BFLOAT16)