ci: Cache verilator build

.github/workflows/ci.yml

@@ -89,7 +89,25 @@ jobs:
         run: |
           bender vendor init
           make CFG_OVERRIDE=cfg/github-ci.hjson sw
+      - name: Generate the RTL
+        working-directory: target/snitch_cluster
+        run: |
+          make CFG_OVERRIDE=cfg/github-ci.hjson rtl
+      - name: Extract file list for Verilator build
+        run: |
+          echo "VLT_SOURCES=$(make echo-vlt-flist) >> $GITHUB_ENV
+          echo $VLT_SOURCES
+          echo $GITHUB_ENV
+      - name: Set up cache for Verilator build
+        id: verilator-cache
+        uses: actions/cache@v3
+        with:
+          path: target/snitch_cluster/bin  # Cache the directory where the simulator binary is stored
+          key: verilator-${{ hashFiles(env.VLT_SOURCES) }}
+          restore-keys: |
+            verilator-
       - name: Build Hardware
+        if: steps.verilator-cache.outputs.cache-hit != 'true'
         working-directory: target/snitch_cluster
         run: |
           make CFG_OVERRIDE=cfg/github-ci.hjson VLT_JOBS=1 bin/snitch_cluster.vlt

target/common/verilator.mk

@@ -2,6 +2,14 @@
 # Licensed under the Apache License, Version 2.0, see LICENSE for details.
 # SPDX-License-Identifier: Apache-2.0
 
+VLT_FLIST = $(VLT_SOURCES)
+VLT_FLIST += $(TB_CC_SOURCES)
+VLT_FLIST += $(VLT_CC_SOURCES)
+
+.PHONY: vlt-flist
+vlt-flist:
+	@echo $(VLT_FLIST)
+
 $(BIN_DIR)/$(TARGET).vlt: $(VLT_SOURCES) $(TB_CC_SOURCES) $(VLT_CC_SOURCES) $(VLT_BUILDDIR)/lib/libfesvr.a | $(BIN_DIR)
 	$(VLT) $(shell $(BENDER) script verilator $(VLT_BENDER)) \
 		$(VLT_FLAGS) -Mdir $(VLT_BUILDDIR) \