[openmp][devicertl] Handle missing clang_tool

[JonChesterfield]

Summary

Fixes github issues/52910

[JonChesterfield]

Spent quite a while trying to get the quoted string to break across two lines without success.

[jdoerfert]

LG

[h-vetinari]

Thanks a lot for the patch! I'm trying to figure out how to apply this to 13.0.0-rc2, but it's not obvious since https://reviews.llvm.org/D111983 has happened in between and reshuffled a bunch of things around.

[JonChesterfield]

We could apply it to the amdgcn file and not the DeviceRTL one - the latter was off by default in 13.x so is less likely to break builds, and the older logic is fine on the happy path.

I don't know the post-bugzilla process for cherry-picking to 13.x, maybe it can be done by GitHub PR these days

[h-vetinari]

OK, just taking the second half of the patch in openmp/libomptarget/deviceRTLs/amdgcn/CMakeLists.txt is actually enough for the backport.

[h-vetinari]

Ah, just saw your comment to that exact effect in the meantime. :)

openmp/libomptarget/DeviceRTL/CMakeLists.txt

 endif()
 
 if (LLVM_DIR)
   # Builds that use pre-installed LLVM have LLVM_DIR set.
   find_program(CLANG_TOOL clang PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
   find_program(LINK_TOOL llvm-link PATHS ${LLVM_TOOLS_BINARY_DIR}
     NO_DEFAULT_PATH)
   find_program(OPT_TOOL opt PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
-  libomptarget_say("Building DeviceRTL. Using clang: ${CLANG_TOOL}")
+  if ((NOT CLANG_TOOL) OR (NOT LINK_TOOL) OR (NOT OPT_TOOL))
+    libomptarget_say("Not building DeviceRTL. Missing clang: ${CLANG_TOOL}, llvm-link: ${LINK_TOOL} or opt: ${OPT_TOOL}")
+    return()
+  else()
+    libomptarget_say("Building DeviceRTL. Using clang: ${CLANG_TOOL}, llvm-link: ${LINK_TOOL} and opt: ${OPT_TOOL}")
+  endif()
 elseif (LLVM_TOOL_CLANG_BUILD AND NOT CMAKE_CROSSCOMPILING AND NOT OPENMP_STANDALONE_BUILD)
   # LLVM in-tree builds may use CMake target names to discover the tools.
   set(CLANG_TOOL $<TARGET_FILE:clang>)
   set(LINK_TOOL $<TARGET_FILE:llvm-link>)
   set(OPT_TOOL $<TARGET_FILE:opt>)
   libomptarget_say("Building DeviceRTL. Using clang from in-tree build")
 else()
   libomptarget_say("Not building DeviceRTL. No appropriate clang found")

openmp/libomptarget/deviceRTLs/amdgcn/CMakeLists.txt

 else()
   libomptarget_say("Not building AMDGCN device RTL: unknown host arch: ${CMAKE_HOST_SYSTEM_PROCESSOR}")
   return()
 endif()
 
 if (LLVM_DIR)
   # Builds that use pre-installed LLVM have LLVM_DIR set.
   find_program(CLANG_TOOL clang PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
-  find_program(LINK_TOOL llvm-link PATHS ${LLVM_TOOLS_BINARY_DIR}
-    NO_DEFAULT_PATH)
+  find_program(LINK_TOOL llvm-link PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
   find_program(OPT_TOOL opt PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
-  libomptarget_say("Building AMDGCN device RTL. Using clang: ${CLANG_TOOL}")
+  if ((NOT CLANG_TOOL) OR (NOT LINK_TOOL) OR (NOT OPT_TOOL))
+    libomptarget_say("Not building AMDGCN device RTL. Missing clang: ${CLANG_TOOL}, llvm-link: ${LINK_TOOL} or opt: ${OPT_TOOL}")
+    return()
+  else()
+    libomptarget_say("Building AMDGCN device RTL. Using clang: ${CLANG_TOOL}, llvm-link: ${LINK_TOOL} and opt: ${OPT_TOOL}")
+  endif()
 elseif (LLVM_TOOL_CLANG_BUILD AND NOT CMAKE_CROSSCOMPILING AND NOT OPENMP_STANDALONE_BUILD)
   # LLVM in-tree builds may use CMake target names to discover the tools.
   set(CLANG_TOOL $<TARGET_FILE:clang>)
   set(LINK_TOOL $<TARGET_FILE:llvm-link>)
   set(OPT_TOOL $<TARGET_FILE:opt>)
   libomptarget_say("Building AMDGCN device RTL. Using clang from in-tree build")
 else()
   libomptarget_say("Not building AMDGCN device RTL. No appropriate clang found")