[cmake][CI] Use llvm_gtest target directly. (#5804)

Upstream now has option for installing these components for use in downstream standalone builds:
llvm/llvm-project@0807986 .

Look for (and prefer) this approach, and update our LLVM builds that we install to use this.

.github/workflows/buildAndTestWindows.yml

@@ -57,7 +57,8 @@ jobs:
             -DLLVM_ENABLE_PROJECTS=mlir -DLLVM_BUILD_EXAMPLES=OFF `
             -DLLVM_TARGETS_TO_BUILD="host" `
             -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=ON `
-            -DLLVM_INSTALL_UTILS=ON -DCMAKE_INSTALL_PREFIX="$(pwd)/../install"
+            -DLLVM_INSTALL_GTEST=ON -DLLVM_INSTALL_UTILS=ON `
+            -DCMAKE_INSTALL_PREFIX="$(pwd)/../install"
           cmake --build . --target install --config Release
           # Grab llvm-lit.py from build tree, we need it.
           cp -v bin/llvm-lit.py ../install/bin/

CMakeLists.txt

@@ -84,12 +84,16 @@ endif ()
   # Handle unittests when building out-of-tree against an installed version of
   # LLVM/MLIR (not a build tree). Adapted from `llvm/flang/CMakeLists.txt`.
   set(CIRCT_GTEST_AVAILABLE 0)
-  set(UNITTEST_DIR ${LLVM_THIRD_PARTY_DIR}/unittest)
-  if (NOT EXISTS ${UNITTEST_DIR}/googletest/include/gtest/gtest.h)
-    set(UNITTEST_DIR ${CMAKE_CURRENT_SOURCE_DIR}/llvm/third-party/unittest)
-  endif()
-  if (EXISTS ${UNITTEST_DIR}/googletest/include/gtest/gtest.h)
-    if (NOT TARGET llvm_gtest)
+  if (TARGET llvm_gtest)
+    # Installed gtest, via LLVM_INSTALL_GTEST.  Preferred.
+    message(STATUS "LLVM GTest found, enabling unittests")
+    set(CIRCT_GTEST_AVAILABLE 1)
+  else()
+    set(UNITTEST_DIR ${LLVM_THIRD_PARTY_DIR}/unittest)
+    if (NOT EXISTS ${UNITTEST_DIR}/googletest/include/gtest/gtest.h)
+      set(UNITTEST_DIR ${CMAKE_CURRENT_SOURCE_DIR}/llvm/third-party/unittest)
+    endif()
+    if (EXISTS ${UNITTEST_DIR}/googletest/include/gtest/gtest.h)
       find_package(Threads)
       add_llvm_library(llvm_gtest
         ${UNITTEST_DIR}/googletest/src/gtest-all.cc
@@ -112,12 +116,12 @@ endif ()
         LINK_COMPONENTS Support # llvm::cl
         BUILDTREE_ONLY
       )
+      set(CIRCT_GTEST_AVAILABLE 1)
+    else()
+      message(WARNING "Skipping unittests since LLVM install does not include \
+        gtest headers and libraries")
+      set(CIRCT_GTEST_AVAILABLE 0)
     endif()
-    set(CIRCT_GTEST_AVAILABLE 1)
-  else()
-    message(WARNING "Skipping unittests since LLVM install does not include \
-      gtest headers and libraries")
-    set(CIRCT_GTEST_AVAILABLE 0)
   endif()
 
 else()

utils/build-llvm.sh

@@ -36,6 +36,7 @@ cmake ../llvm \
   -DLLVM_ENABLE_OCAMLDOC=OFF \
   -DLLVM_ENABLE_PROJECTS='mlir' \
   -DLLVM_INSTALL_UTILS=ON \
+  -DLLVM_INSTALL_GTEST=ON \
   -DLLVM_OPTIMIZED_TABLEGEN=ON \
   -DLLVM_TARGETS_TO_BUILD="host" \
   $EXTRA_ARGS