[PATCH] D81545: [cmake] Don't pass -z discard-unused to Illumos ld

[Rainer Orth via Phabricator via llvm-commits]

ro created this revision.
ro added reviewers: chandlerc, scott.linder, hans, stephenneuendorffer.
ro added a project: LLVM.
Herald added subscribers: fedor.sergeev, mgorny.

I'm currently working to port `libc++` to Solaris.  There exists a slightly bitrotten port
already, which was done on Illumos, an OpenSolaris derivative.  In order not to break that
port with my work, I need to test the result on both Solaris and Illumos.  While doing so,
it turned out that Illumos `ld` doesn't support the `-z discard-sections=unused` option
currently used on SunOS unconditionally.

While there exists a patch <https://github.com/OpenIndiana/oi-userland/blob/oi/hipster/components/developer/clang-90/patches/02-cmake_modules_AddLLVM.cmake.patch>
for LLVM 9.0 in the OpenIndiana repository, it apparently hasn't been submitted
upstream and is completely wrong: it replaces `-z discard-sections=unused` with
`-z ignore`.  In terms of the equivalent `gld` options, this means replacing `--gc-sections`
with `--as-needed`.

This patch instead tests if the linker actually supports the option before using it.

Tested on `amd64-pc-solaris2.11` (all of Solaris 11.4, 11.3 and OpenIndiana 2020.04).

Ok for master?


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D81545

Files:
  llvm/cmake/modules/AddLLVM.cmake


Index: llvm/cmake/modules/AddLLVM.cmake
===================================================================
--- llvm/cmake/modules/AddLLVM.cmake
+++ llvm/cmake/modules/AddLLVM.cmake
@@ -240,8 +240,14 @@
         set_property(TARGET ${target_name} APPEND_STRING PROPERTY
                      LINK_FLAGS " -Wl,-dead_strip")
       elseif(${CMAKE_SYSTEM_NAME} MATCHES "SunOS")
-        set_property(TARGET ${target_name} APPEND_STRING PROPERTY
-                     LINK_FLAGS " -Wl,-z -Wl,discard-unused=sections")
+        # Support for ld -z discard-unused=sections was only added in
+        # Solaris 11.4.
+        include(CheckLinkerFlag)
+        check_linker_flag("-Wl,-z,discard-unused=sections" LINKER_SUPPORTS_Z_DISCARD_UNUSED)
+        if (LINKER_SUPPORTS_Z_DISCARD_UNUSED)
+          set_property(TARGET ${target_name} APPEND_STRING PROPERTY
+                       LINK_FLAGS " -Wl,-z,discard-unused=sections")
+        endif()
       elseif(NOT WIN32 AND NOT LLVM_LINKER_IS_GOLD AND
              NOT ${CMAKE_SYSTEM_NAME} MATCHES "OpenBSD|AIX")
         # Object files are compiled with -ffunction-data-sections.


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