[cmake] Rather than forcing parts of the build that don't depend on LLVM to define LLVM_COMMON_DEPENDS, just have add_swift_host_library respect the global if it is set.

Author: gottesmm

cmake/modules/AddSwift.cmake

@@ -477,7 +477,17 @@ function(add_swift_host_library name)
   endif()
 
   add_library(${name} ${libkind} ${ASHL_SOURCES})
-  add_dependencies(${name} ${LLVM_COMMON_DEPENDS})
+
+  # Respect LLVM_COMMON_DEPENDS if it is set.
+  #
+  # LLVM_COMMON_DEPENDS if a global variable set in ./lib that provides targets
+  # such as swift-syntax or tblgen that all LLVM/Swift based tools depend on. If
+  # we don't have it defined, then do not add the dependency since some parts of
+  # swift host tools do not interact with LLVM/Swift tools and do not define
+  # LLVM_COMMON_DEPENDS.
+  if (LLVM_COMMON_DEPENDS)
+    add_dependencies(${name} ${LLVM_COMMON_DEPENDS})
+  endif()
   if (NOT ASHL_PURE_SWIFT)
     llvm_update_compile_flags(${name})
   endif()
@@ -628,7 +638,17 @@ function(add_swift_host_tool executable)
   # Force executables linker language to be CXX so that we do not link using the
   # host toolchain swiftc.
   set_target_properties(${executable} PROPERTIES LINKER_LANGUAGE CXX)
-  add_dependencies(${executable} ${LLVM_COMMON_DEPENDS})
+
+  # Respect LLVM_COMMON_DEPENDS if it is set.
+  #
+  # LLVM_COMMON_DEPENDS if a global variable set in ./lib that provides targets
+  # such as swift-syntax or tblgen that all LLVM/Swift based tools depend on. If
+  # we don't have it defined, then do not add the dependency since some parts of
+  # swift host tools do not interact with LLVM/Swift tools and do not define
+  # LLVM_COMMON_DEPENDS.
+  if (LLVM_COMMON_DEPENDS)
+    add_dependencies(${executable} ${LLVM_COMMON_DEPENDS})
+  endif()
 
   set_target_properties(${executable} PROPERTIES
     FOLDER "Swift executables")

validation-test/BuildSystem/swift-cmake/CMakeLists.txt

@@ -1,18 +1,3 @@
-# In the absence of fine grained tablegen dependencies we need to ensure that
-# Swift's libraries all build after the LLVM & Clang tablegen-generated headers
-# are generated. When building out-of-tree (as with build-script) LLVM & Clang's
-# CMake configuration files create these targets as dummies so we can safely
-# depend on them directly here (See: SR-6026)
-# LLVM_COMMON_DEPENDS is a construct from the LLVM build system. It is a special
-# purpose variable that provides common dependencies for all libraries, and
-# executables generated when it is set. CMake's scoping rules enforce that these
-# new dependencies will only be added to targets created under Swift's lib
-# directory.
-list(APPEND LLVM_COMMON_DEPENDS intrinsics_gen clang-tablegen-targets)
-
-# Add generated libSyntax headers to global dependencies.
-list(APPEND LLVM_COMMON_DEPENDS swift-syntax-generated-headers)
-list(APPEND LLVM_COMMON_DEPENDS swift-parse-syntax-generated-headers)
 
 add_swift_host_library(TestCPPLib
   STATIC