[llvm-branch-commits] [llvm] release/21.x: [flang-rt] Remove hard-coded dependency on compiler-rt path on Windows (#150244) (PR #150764)

[via llvm-branch-commits]

https://github.com/llvmbot updated https://github.com/llvm/llvm-project/pull/150764

>From 96e15ebab5ae593cd5c8d84ce9d787d81f4b756d Mon Sep 17 00:00:00 2001
From: David Truby <david.truby at arm.com>
Date: Sat, 26 Jul 2025 14:42:42 +0100
Subject: [PATCH] [flang-rt] Remove hard-coded dependency on compiler-rt path
 on Windows (#150244)

This fixes an issue where if the build folder is no longer present flang
cannot link anything on Windows because the path to compiler-rt in the
binary is hard-coded. Flang already links compiler-rt on Windows so it
isn't necessary for flang-rt to specify that it depends on compiler-rt
at all, other than for the unit tests, so instead we can move that logic
into the unit test compile lines.

(cherry picked from commit c20a95a7ddd8219f3e587e335a0a8e3f4613fc47)
---
 flang-rt/cmake/modules/AddFlangRT.cmake | 21 ---------------------
 flang-rt/unittests/CMakeLists.txt       | 23 +++++++++++++++++++++++
 2 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/flang-rt/cmake/modules/AddFlangRT.cmake b/flang-rt/cmake/modules/AddFlangRT.cmake
index e51590fdae3d3..58541609829c4 100644
--- a/flang-rt/cmake/modules/AddFlangRT.cmake
+++ b/flang-rt/cmake/modules/AddFlangRT.cmake
@@ -286,27 +286,6 @@ function (add_flangrt_library name)
       target_compile_options(${tgtname} PUBLIC -U_LIBCPP_ENABLE_ASSERTIONS)
     endif ()
 
-    # Flang/Clang (including clang-cl) -compiled programs targeting the MSVC ABI
-    # should only depend on msvcrt/ucrt. LLVM still emits libgcc/compiler-rt
-    # functions in some cases like 128-bit integer math (__udivti3, __modti3,
-    # __fixsfti, __floattidf, ...) that msvc does not support. We are injecting a
-    # dependency to Compiler-RT's builtin library where these are implemented.
-    if (MSVC AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-      if (FLANG_RT_BUILTINS_LIBRARY)
-        target_compile_options(${tgtname} PRIVATE "$<$<COMPILE_LANGUAGE:CXX,C>:-Xclang>" "$<$<COMPILE_LANGUAGE:CXX,C>:--dependent-lib=${FLANG_RT_BUILTINS_LIBRARY}>")
-      endif ()
-    endif ()
-    if (MSVC AND CMAKE_Fortran_COMPILER_ID STREQUAL "LLVMFlang")
-      if (FLANG_RT_BUILTINS_LIBRARY)
-        target_compile_options(${tgtname} PRIVATE "$<$<COMPILE_LANGUAGE:Fortran>:-Xflang>" "$<$<COMPILE_LANGUAGE:Fortran>:--dependent-lib=${FLANG_RT_BUILTINS_LIBRARY}>")
-      else ()
-        message(WARNING "Did not find libclang_rt.builtins.lib.
-          LLVM may emit builtins that are not implemented in msvcrt/ucrt and
-          instead falls back to builtins from Compiler-RT. Linking with ${tgtname}
-          may result in a linker error.")
-      endif ()
-    endif ()
-
     # Non-GTest unittests depend on LLVMSupport
     if (ARG_LINK_TO_LLVM)
       if (LLVM_LINK_LLVM_DYLIB)
diff --git a/flang-rt/unittests/CMakeLists.txt b/flang-rt/unittests/CMakeLists.txt
index 5282196174134..831bc8a4c2906 100644
--- a/flang-rt/unittests/CMakeLists.txt
+++ b/flang-rt/unittests/CMakeLists.txt
@@ -60,6 +60,27 @@ function(add_flangrt_unittest_offload_properties target)
   endif()
 endfunction()
 
+# flang-rt on Windows requires compiler-rt for some symbols. For binaries built
+# with flang this dependency is added by the flang driver, but since the unit
+# tests are built with clang we need to add the dependency manually.
+function(add_flangrt_dependent_libs target)
+  if (MSVC AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+    if (FLANG_RT_BUILTINS_LIBRARY)
+      target_compile_options(${target} PRIVATE "$<$<COMPILE_LANGUAGE:CXX,C>:-Xclang>" "$<$<COMPILE_LANGUAGE:CXX,C>:--dependent-lib=${FLANG_RT_BUILTINS_LIBRARY}>")
+    endif ()
+  endif ()
+  if (MSVC AND CMAKE_Fortran_COMPILER_ID STREQUAL "LLVMFlang")
+    if (FLANG_RT_BUILTINS_LIBRARY)
+      target_compile_options(${target} PRIVATE "$<$<COMPILE_LANGUAGE:Fortran>:-Xflang>" "$<$<COMPILE_LANGUAGE:Fortran>:--dependent-lib=${FLANG_RT_BUILTINS_LIBRARY}>")
+    else ()
+      message(WARNING "Did not find libclang_rt.builtins.lib.
+        LLVM may emit builtins that are not implemented in msvcrt/ucrt and
+        instead falls back to builtins from Compiler-RT. Linking with ${tgtname}
+        may result in a linker error.")
+    endif ()
+  endif ()
+endfunction()
+
 
 function(add_flangrt_unittest test_dirname)
   cmake_parse_arguments(ARG
@@ -72,6 +93,7 @@ function(add_flangrt_unittest test_dirname)
 
   target_link_libraries(${test_dirname} PRIVATE ${ARG_LINK_LIBS})
   add_flangrt_unittest_offload_properties(${test_dirname})
+  add_flangrt_dependent_libs(${test_dirname})
 
   # Required because LLVMSupport is compiled with this option.
   # FIXME: According to CMake documentation, this is the default. Why is it
@@ -99,6 +121,7 @@ function(add_flangrt_nongtest_unittest test_name)
   set_target_properties(${test_name}${suffix} PROPERTIES FOLDER "Flang-RT/Tests/Unit")
 
   target_link_libraries(${test_name}${suffix} PRIVATE NonGTestTesting ${ARG_LINK_LIBS})
+  add_flangrt_dependent_libs(${test_name}${suffix})
 
   if(NOT ARG_SLOW_TEST)
     add_dependencies(FlangRTUnitTests ${test_name}${suffix})