[compiler-rt] [compiler-rt] Fix detecting _Float16 support for secondary targets (PR #117813)

[Alexander Richardson via llvm-commits]

https://github.com/arichardson created https://github.com/llvm/llvm-project/pull/117813

It turns out we were not passing -m32 to the check_c_source_compiles()
invocation since CMAKE_REQUIRE_FLAGS needs to be string separated list and
we were passing a ;-separated CMake list which appears to be parsed by
CMake as 'ignore all arguments beyond the first'.
Fix this by transforming the list to a command line first.

With this change, Clang 17 no longer claims to support _Float16 for i386.


>From 31addad47c4f7274ec8871f4fb7ad9fa0c38e473 Mon Sep 17 00:00:00 2001
From: Alex Richardson <alexrichardson at google.com>
Date: Tue, 26 Nov 2024 16:05:40 -0800
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
 =?UTF-8?q?l=20version?=
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Created using spr 1.3.6-beta.1
---
 compiler-rt/lib/builtins/CMakeLists.txt | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/compiler-rt/lib/builtins/CMakeLists.txt b/compiler-rt/lib/builtins/CMakeLists.txt
index 42d197f2b08d00..73c1b5062ec9a9 100644
--- a/compiler-rt/lib/builtins/CMakeLists.txt
+++ b/compiler-rt/lib/builtins/CMakeLists.txt
@@ -850,9 +850,12 @@ else ()
     if (CAN_TARGET_${arch})
       cmake_push_check_state()
       # TODO: we should probably make most of the checks in builtin-config depend on the target flags.
-      message(STATUS "Performing additional configure checks with target flags: ${TARGET_${arch}_CFLAGS}")
       set(BUILTIN_CFLAGS_${arch} ${BUILTIN_CFLAGS})
-      list(APPEND CMAKE_REQUIRED_FLAGS ${TARGET_${arch}_CFLAGS} ${BUILTIN_CFLAGS_${arch}})
+      # CMAKE_REQUIRED_FLAGS must be a space separated string but unlike TARGET_${arch}_CFLAGS,
+      # BUILTIN_CFLAGS_${arch} is a CMake list, so we have to join it to create a valid command line.
+      list(JOIN BUILTIN_CFLAGS " " CMAKE_REQUIRED_FLAGS)
+      set(CMAKE_REQUIRED_FLAGS "${TARGET_${arch}_CFLAGS} ${BUILTIN_CFLAGS_${arch}}")
+      message(STATUS "Performing additional configure checks with target flags: ${CMAKE_REQUIRED_FLAGS}")
       # For ARM archs, exclude any VFP builtins if VFP is not supported
       if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7m|armv7em|armv8m.main|armv8.1m.main)$")
         string(REPLACE ";" " " _TARGET_${arch}_CFLAGS "${TARGET_${arch}_CFLAGS}")