[build] Check RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES for libc also

[petrhosek]

When checking whether we need to build libc-hdrgen, we need to check LLVM_ENABLE_RUNTIMES and RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES, just the former is not sufficient since libc may be enabled only for certain targets.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Petr Hosek (petrhosek)

Changes

When checking whether we need to build libc-hdrgen, we need to check LLVM_ENABLE_RUNTIMES and RUNTIMES_${target}_LLVM_ENABLE_RUNTIMES, just the former is not sufficient since libc may be enabled only for certain targets.

---

Full diff: https://github.com/llvm/llvm-project/pull/82561.diff

2 Files Affected:

• (modified) libc/CMakeLists.txt (+15-2)
• (modified) llvm/CMakeLists.txt (+13-1)

diff --git a/libc/CMakeLists.txt b/libc/CMakeLists.txt
index 3d775736616745..73877fd3d7fd02 100644
--- a/libc/CMakeLists.txt
+++ b/libc/CMakeLists.txt
@@ -57,9 +57,21 @@ if(LLVM_LIBC_FULL_BUILD OR LIBC_GPU_BUILD OR LIBC_GPU_ARCHITECTURES)
   endif()
 endif()
 
+set(NEED_LIBC_HDRGEN FALSE)
+if(NOT LLVM_RUNTIMES_BUILD)
+  if("libc" IN_LIST LLVM_ENABLE_RUNTIMES)
+    set(NEED_LIBC_HDRGEN TRUE)
+  else()
+    foreach(_name ${LLVM_RUNTIME_TARGETS})
+      if("libc" IN_LIST RUNTIMES_${_name}_LLVM_ENABLE_RUNTIMES)
+        set(NEED_LIBC_HDRGEN TRUE)
+        break()
+      endif()
+    endforeach()
+  endif()
+endif()
 option(LIBC_HDRGEN_ONLY "Only build the 'libc-hdrgen' executable" OFF)
-if(("libc" IN_LIST LLVM_ENABLE_RUNTIMES AND NOT LLVM_RUNTIMES_BUILD) OR 
-   LIBC_HDRGEN_ONLY)
+if(LIBC_HDRGEN_ONLY OR NEED_LIBC_HDRGEN)
   # When libc is build as part of the runtimes/bootstrap build's CMake run, we
   # only need to build the host tools to build the libc. So, we just do enough
   # to build libc-hdrgen and return.
@@ -70,6 +82,7 @@ if(("libc" IN_LIST LLVM_ENABLE_RUNTIMES AND NOT LLVM_RUNTIMES_BUILD) OR
   endif()
   return()
 endif()
+unset(NEED_LIBC_HDRGEN)
 
 option(LIBC_CMAKE_VERBOSE_LOGGING
   "Log details warnings and notifications during CMake configuration." OFF)
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index a760a19efcb6b1..fe0091be9d9494 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -168,7 +168,18 @@ foreach(proj IN LISTS LLVM_ENABLE_RUNTIMES)
   endif()
 endforeach()
 
-if ("libc" IN_LIST LLVM_ENABLE_RUNTIMES)
+set(NEED_LIBC_HDRGEN FALSE)
+if("libc" IN_LIST LLVM_ENABLE_RUNTIMES)
+  set(NEED_LIBC_HDRGEN TRUE)
+else()
+  foreach(_name ${LLVM_RUNTIME_TARGETS})
+    if("libc" IN_LIST RUNTIMES_${_name}_LLVM_ENABLE_RUNTIMES)
+      set(NEED_LIBC_HDRGEN TRUE)
+      break()
+    endif()
+  endforeach()
+endif()
+if(NEED_LIBC_HDRGEN)
   # To build the libc runtime, we need to be able to build few libc build
   # tools from the "libc" project. So, we add it to the list of enabled
   # projects.
@@ -177,6 +188,7 @@ if ("libc" IN_LIST LLVM_ENABLE_RUNTIMES)
     list(APPEND LLVM_ENABLE_PROJECTS "libc")
   endif()
 endif()
+unset(NEED_LIBC_HDRGEN)
 
 # LLVM_ENABLE_PROJECTS_USED is `ON` if the user has ever used the
 # `LLVM_ENABLE_PROJECTS` CMake cache variable.  This exists for

[jhuber6]

I did this in #82513 as well, but it adds the extra runtimes things. Don't know if that's the best way to express it, but I'd really prefer to not need to force people to change the rest of their build to enable the cross compiling targets.

[petrhosek]

I did this in #82513 as well, but it adds the extra runtimes things. Don't know if that's the best way to express it, but I'd really prefer to not need to force people to change the rest of their build to enable the cross compiling targets.

I have more changes in the pipeline that redo the handling of the default target, this is just a preparatory change that addresses an existing limitation.

[jhuber6]

I'll approve this to move along whatever you have planned. This should allow using it with the existing support, however I strongly think that we need an "append only" solution if that makes sense. I want a solution that only adds CMake arguments so users can just copy-paste something or use some shorthand that does the same thing.