Support objcache when compiling Verilated files with cmake.

Changes

@@ -29,6 +29,7 @@ Verilator 5.029 devel
 * Support basic dist constraints (#5431). [Arkadiusz Kozdra, Antmicro Ltd.]
 * Support inside array constraints (#5448). [Arkadiusz Kozdra, Antmicro Ltd.]
 * Support DPI imports and exports with double underscores (#5481).
+* Support objcache when compiling Verilated files with cmake.
 * Add error on instances without parenthesis.
 * Add partial coverage symbol and branch data in lcov info files (#5388). [Andrew Nolte]
 * Add method to check if there are VPI callbacks of the given type (#5399). [Kaleb Barrett]

test_regress/t/t_a7_hier_block_cmake.py

@@ -8,6 +8,7 @@
 # SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
 
 import vltest_bootstrap
+import multiprocessing
 
 # If a test fails, broken .cmake may disturb the next run
 test.clean_objs()
@@ -29,7 +30,7 @@ test.run(logfile=test.obj_dir + "/cmake.log",
 test.run(logfile=test.obj_dir + "/build.log",
          cmd=[
              'cd "' + test.obj_dir + '" && cmake --build', '.', ('-v' if test.verbose else ''),
-             '--', "CXX_FLAGS=" + str(threads)
+             '-j ' + str(multiprocessing.cpu_count()), '--', "CXX_FLAGS=" + str(threads)
          ])
 
 test.run(logfile=test.obj_dir + "/run.log",

verilator-config.cmake.in

@@ -227,6 +227,37 @@ function(verilate TARGET)
         set(COMPILER gcc)
     endif()
 
+    set(OBJCACHE "" CACHE STRING "Path for ccache, auto-detected if empty")
+    option(OBJCACHE_ENABLED "Compile Verilator with ccache" ON)
+
+    if(OBJCACHE_ENABLED)
+        if(OBJCACHE STREQUAL "")
+            find_program(OBJCACHE_PATH ccache)
+            if(OBJCACHE_PATH STREQUAL "OBJCACHE_PATH-NOTFOUND")
+                set(OBJCACHE_PATH "")
+            endif()
+        else()
+            set(OBJCACHE_PATH "${OBJCACHE}")
+        endif()
+        if(NOT OBJCACHE_PATH STREQUAL "")
+            execute_process(
+                COMMAND "${OBJCACHE_PATH}" --version
+                OUTPUT_VARIABLE objcache_version
+            )
+            string(
+                REGEX MATCH
+                "[^\n\r]+"
+                objcache_version
+                "${objcache_version}"
+            )
+            message(
+                STATUS
+                "Found ccache: ${OBJCACHE_PATH} (\"${objcache_version}\")"
+            )
+            set(CMAKE_CXX_COMPILER_LAUNCHER "${OBJCACHE_PATH}")
+        endif()
+    endif()
+
     get_target_property(BINARY_DIR "${TARGET}" BINARY_DIR)
     get_target_property(TARGET_NAME "${TARGET}" NAME)
     set(VDIR