Use [[maybe_unused]] instead of YS_ATTRIBUTE(unused).

[[maybe_unused]] is available since C++17, so this commit adds
a polyfill YS_MAYBE_UNUSED. Once we require C++17 we can drop it.

2 files changed, 18 insertions, 10 deletions

diff --git a/kernel/yosys.h b/kernel/yosys.h
index b9b6b24b1..f1646d6bc 100644
--- a/kernel/yosys.h
+++ b/kernel/yosys.h
@@ -145,6 +145,14 @@ extern Tcl_Obj *Tcl_ObjSetVar2(Tcl_Interp *interp, Tcl_Obj *part1Ptr, Tcl_Obj *p
 #endif
 
 #if __cplusplus >= 201703L
+#  define YS_MAYBE_UNUSED [[maybe_unused]];
+#elif defined(__GNUC__) || defined(__clang__)
+#  define YS_MAYBE_UNUSED __attribute__((__unused__))
+#else
+#  define YS_MAYBE_UNUSED
+#endif
+
+#if __cplusplus >= 201703L
 #  define YS_FALLTHROUGH [[fallthrough]];
 #elif defined(__clang__)
 #  define YS_FALLTHROUGH [[clang::fallthrough]];
diff --git a/passes/pmgen/pmgen.py b/passes/pmgen/pmgen.py
index df0ffaff2..592a26fa6 100644
--- a/passes/pmgen/pmgen.py
+++ b/passes/pmgen/pmgen.py
@@ -589,7 +589,7 @@ with open(outfile, "w") as f:
         if block["type"] in ("match", "code"):
             print("  // {}".format(block["src"]), file=f)
 
-        print("  void block_{}(int recursion YS_ATTRIBUTE(unused)) {{".format(index), file=f)
+        print("  void block_{}(int recursion YS_MAYBE_UNUSED) {{".format(index), file=f)
         current_pattern, current_subpattern = block["pattern"]
 
         if block["type"] == "final":
@@ -636,17 +636,17 @@ with open(outfile, "w") as f:
         for s in sorted(const_st):
             t = state_types[current_pattern][s]
             if t.endswith("*"):
-                print("    {} const &{} YS_ATTRIBUTE(unused) = st_{}.{};".format(t, s, current_pattern, s), file=f)
+                print("    {} const &{} YS_MAYBE_UNUSED = st_{}.{};".format(t, s, current_pattern, s), file=f)
             else:
-                print("    const {} &{} YS_ATTRIBUTE(unused) = st_{}.{};".format(t, s, current_pattern, s), file=f)
+                print("    const {} &{} YS_MAYBE_UNUSED = st_{}.{};".format(t, s, current_pattern, s), file=f)
 
         for s in sorted(nonconst_st):
             t = state_types[current_pattern][s]
-            print("    {} &{} YS_ATTRIBUTE(unused) = st_{}.{};".format(t, s, current_pattern, s), file=f)
+            print("    {} &{} YS_MAYBE_UNUSED = st_{}.{};".format(t, s, current_pattern, s), file=f)
 
         for u in sorted(udata_types[current_pattern].keys()):
             t = udata_types[current_pattern][u]
-            print("    {} &{} YS_ATTRIBUTE(unused) = ud_{}.{};".format(t, u, current_pattern, u), file=f)
+            print("    {} &{} YS_MAYBE_UNUSED = ud_{}.{};".format(t, u, current_pattern, u), file=f)
 
         if len(restore_st):
             print("", file=f)
@@ -676,7 +676,7 @@ with open(outfile, "w") as f:
 
             print("", file=f)
             print("rollback_label:", file=f)
-            print("    YS_ATTRIBUTE(unused);", file=f)
+            print("    YS_MAYBE_UNUSED;", file=f)
 
             if len(block["fcode"]):
                 print("#define accept do { accept_cnt++; on_accept(); } while(0)", file=f)
@@ -684,7 +684,7 @@ with open(outfile, "w") as f:
                 for line in block["fcode"]:
                     print("  " + line, file=f)
                 print("finish_label:", file=f)
-                print("    YS_ATTRIBUTE(unused);", file=f)
+                print("    YS_MAYBE_UNUSED;", file=f)
                 print("#undef accept", file=f)
                 print("#undef finish", file=f)
 
@@ -733,13 +733,13 @@ with open(outfile, "w") as f:
             valueidx = 1
             for item in block["setup"]:
                 if item[0] == "slice":
-                    print("        const int &{} YS_ATTRIBUTE(unused) = std::get<{}>(cells[_pmg_idx]);".format(item[1], valueidx), file=f)
+                    print("        const int &{} YS_MAYBE_UNUSED = std::get<{}>(cells[_pmg_idx]);".format(item[1], valueidx), file=f)
                     valueidx += 1
                 if item[0] == "choice":
-                    print("        const {} &{} YS_ATTRIBUTE(unused) = std::get<{}>(cells[_pmg_idx]);".format(item[1], item[2], valueidx), file=f)
+                    print("        const {} &{} YS_MAYBE_UNUSED = std::get<{}>(cells[_pmg_idx]);".format(item[1], item[2], valueidx), file=f)
                     valueidx += 1
                 if item[0] == "define":
-                    print("        const {} &{} YS_ATTRIBUTE(unused) = std::get<{}>(cells[_pmg_idx]);".format(item[1], item[2], valueidx), file=f)
+                    print("        const {} &{} YS_MAYBE_UNUSED = std::get<{}>(cells[_pmg_idx]);".format(item[1], item[2], valueidx), file=f)
                     valueidx += 1
             print("        if (blacklist_cells.count({})) continue;".format(block["cell"]), file=f)
             for expr in block["filter"]: