Merge pull request #5894 from YosysHQ/gcc_16

Bump CI to gcc-16 and fix warnings

.github/workflows/test-compile.yml

@@ -47,7 +47,7 @@ jobs:
           - 'gcc-11'
           # newest, make sure to update maximum standard step to match
           - 'clang-22'
-          - 'gcc-15'
+          - 'gcc-16'
         include:
           # macOS x86
           - os: macos-15-intel
@@ -96,7 +96,7 @@ jobs:
 
       # maximum standard, only on newest compilers
       - name: Build C++26
-        if: ${{ matrix.compiler == 'clang-22' || matrix.compiler == 'gcc-15' }}
+        if: ${{ matrix.compiler == 'clang-22' || matrix.compiler == 'gcc-16' }}
         shell: bash
         run: |
           rm -rf build

backends/jny/jny.cc

@@ -275,7 +275,7 @@ struct JnyWriter
         const auto _indent = gen_indent(indent_level);
 
         bool first_port{true};
-        for (auto con : port_cell->connections()) {
+        for (auto& con : port_cell->connections()) {
             if (!first_port)
                 f << ",\n";
 

passes/cmds/abstract.cc

@@ -469,6 +469,7 @@ struct AbstractPass : public Pass {
 			switch (enable) {
 				case Enable::Always:
 					log_assert(false);
+					YS_FALLTHROUGH
 				case Enable::ActiveLow:
 				case Enable::ActiveHigh: {
 					if (enable_name.empty())

passes/cmds/sdc/sdc.cc

@@ -149,7 +149,7 @@ struct SdcObjects {
 				path += "/";
 			path += name;
 			design_cells.push_back(std::make_pair(path, cell));
-			for (auto pin : cell->connections()) {
+			for (auto& pin : cell->connections()) {
 				IdString pin_name = pin.first;
 				std::string pin_name_sdc = path + "/" + pin.first.str().substr(1);
 				design_pins.push_back(std::make_pair(pin_name_sdc, std::make_pair(cell, pin_name)));

passes/opt/opt_merge.cc

@@ -324,7 +324,7 @@ struct OptMergeThreadWorker
 			CellEqualOp> known_cells(0, CellHashOp(), CellEqualOp(*this));
 
 		std::vector<DuplicateCell> duplicates;
-		for (const std::vector<std::vector<CellHash>> &buckets : in.bucketed_cell_hashes) {
+		for (std::vector<std::vector<CellHash>> &buckets : in.bucketed_cell_hashes) {
 			// Clear out our buckets as we go. This keeps the work of deallocation
 			// off the main thread.
 			std::vector<CellHash> bucket = std::move(buckets[index]);