smtbmc: Add --track-assumes and --minimize-assumes options

The --track-assumes option makes smtbmc keep track of which assumptions
were used by the solver when reaching an unsat case and to output that
set of assumptions. This is particularly useful to debug PREUNSAT
failures.

The --minimize-assumes option can be used in addition to --track-assumes
which will cause smtbmc to spend additional solving effort to produce a
minimal set of assumptions that are sufficient to cause the unsat
result.

backends/smt2/smtbmc.py

@@ -57,6 +57,8 @@ keep_going = False
 check_witness = False
 detect_loops = False
 incremental = None
+track_assumes = False
+minimize_assumes = False
 so = SmtOpts()
 
 
@@ -189,6 +191,15 @@ def help():
     --incremental
         run in incremental mode (experimental)
 
+    --track-assumes
+        track individual assumptions and report a subset of used
+        assumptions that are sufficient for the reported outcome. This
+        can be used to debug PREUNSAT failures as well as to find a
+        smaller set of sufficient assumptions.
+
+    --minimize-assumes
+        when using --track-assumes, solve for a minimal set of sufficient assumptions.
+
 """ + so.helpmsg())
 
 def usage():
@@ -200,7 +211,8 @@ try:
     opts, args = getopt.getopt(sys.argv[1:], so.shortopts + "t:higcm:", so.longopts +
             ["help", "final-only", "assume-skipped=", "smtc=", "cex=", "aig=", "aig-noheader", "yw=", "btorwit=", "presat",
              "dump-vcd=", "dump-yw=", "dump-vlogtb=", "vlogtb-top=", "dump-smtc=", "dump-all", "noinfo", "append=",
-             "smtc-init", "smtc-top=", "noinit", "binary", "keep-going", "check-witness", "detect-loops", "incremental"])
+             "smtc-init", "smtc-top=", "noinit", "binary", "keep-going", "check-witness", "detect-loops", "incremental",
+             "track-assumes", "minimize-assumes"])
 except:
     usage()
 
@@ -289,6 +301,10 @@ for o, a in opts:
     elif o == "--incremental":
         from smtbmc_incremental import Incremental
         incremental = Incremental()
+    elif o == "--track-assumes":
+        track_assumes = True
+    elif o == "--minimize-assumes":
+        minimize_assumes = True
     elif so.handle(o, a):
         pass
     else:
@@ -447,6 +463,9 @@ def get_constr_expr(db, state, final=False, getvalues=False, individual=False):
 
 smt = SmtIo(opts=so)
 
+if track_assumes:
+    smt.smt2_options[':produce-unsat-assumptions'] = 'true'
+
 if noinfo and vcdfile is None and vlogtbfile is None and outconstr is None:
     smt.produce_models = False
 
@@ -1497,6 +1516,44 @@ def get_active_assert_map(step, active):
 
     return assert_map
 
+assume_enables = {}
+
+def declare_assume_enables():
+    def recurse(mod, path, key_base=()):
+        for expr, desc in smt.modinfo[mod].assumes.items():
+            enable = f"|assume_enable {len(assume_enables)}|"
+            smt.smt2_assumptions[(expr, key_base)] = enable
+            smt.write(f"(declare-const {enable} Bool)")
+            assume_enables[(expr, key_base)] = (enable, path, desc)
+
+        for cell, submod in smt.modinfo[mod].cells.items():
+            recurse(submod, f"{path}.{cell}", (mod, cell, key_base))
+
+    recurse(topmod, topmod)
+
+if track_assumes:
+    declare_assume_enables()
+
+def smt_assert_design_assumes(step):
+    if not track_assumes:
+        smt_assert_consequent("(|%s_u| s%d)" % (topmod, step))
+        return
+
+    if not assume_enables:
+        return
+
+    def expr_for_assume(assume_key, base=None):
+        expr, key_base = assume_key
+        expr_prefix = f"(|{expr}| "
+        expr_suffix = ")"
+        while key_base:
+            mod, cell, key_base = key_base
+            expr_prefix += f"(|{mod}_h {cell}| "
+            expr_suffix += ")"
+        return f"{expr_prefix} s{step}{expr_suffix}"
+
+    for assume_key, (enable, path, desc) in assume_enables.items():
+        smt_assert_consequent(f"(=> {enable} {expr_for_assume(assume_key)})")
 
 states = list()
 asserts_antecedent_cache = [list()]
@@ -1651,6 +1708,13 @@ def smt_check_sat(expected=["sat", "unsat"]):
         smt_forall_assert()
     return smt.check_sat(expected=expected)
 
+def report_tracked_assumptions(msg):
+    if track_assumes:
+        print_msg(msg)
+        for key in smt.get_unsat_assumptions(minimize=minimize_assumes):
+            enable, path, descr = assume_enables[key]
+            print_msg(f"  In {path}: {descr}")
+
 
 if incremental:
     incremental.mainloop()
@@ -1664,7 +1728,7 @@ elif tempind:
             break
 
         smt_state(step)
-        smt_assert_consequent("(|%s_u| s%d)" % (topmod, step))
+        smt_assert_design_assumes(step)
         smt_assert_antecedent("(|%s_h| s%d)" % (topmod, step))
         smt_assert_antecedent("(not (|%s_is| s%d))" % (topmod, step))
         smt_assert_consequent(get_constr_expr(constr_assumes, step))
@@ -1707,6 +1771,7 @@ elif tempind:
 
         else:
             print_msg("Temporal induction successful.")
+            report_tracked_assumptions("Used assumptions:")
             retstatus = "PASSED"
             break
 
@@ -1732,7 +1797,7 @@ elif covermode:
 
     while step < num_steps:
         smt_state(step)
-        smt_assert_consequent("(|%s_u| s%d)" % (topmod, step))
+        smt_assert_design_assumes(step)
         smt_assert_antecedent("(|%s_h| s%d)" % (topmod, step))
         smt_assert_consequent(get_constr_expr(constr_assumes, step))
 
@@ -1753,6 +1818,7 @@ elif covermode:
             smt_assert("(distinct (covers_%d s%d) #b%s)" % (coveridx, step, "0" * len(cover_desc)))
 
             if smt_check_sat() == "unsat":
+                report_tracked_assumptions("Used assumptions:")
                 smt_pop()
                 break
 
@@ -1761,13 +1827,14 @@ elif covermode:
                     print_msg("Appending additional step %d." % i)
                     smt_state(i)
                     smt_assert_antecedent("(not (|%s_is| s%d))" % (topmod, i))
-                    smt_assert_consequent("(|%s_u| s%d)" % (topmod, i))
+                    smt_assert_design_assumes(i)
                     smt_assert_antecedent("(|%s_h| s%d)" % (topmod, i))
                     smt_assert_antecedent("(|%s_t| s%d s%d)" % (topmod, i-1, i))
                     smt_assert_consequent(get_constr_expr(constr_assumes, i))
                 print_msg("Re-solving with appended steps..")
                 if smt_check_sat() == "unsat":
                     print("%s Cannot appended steps without violating assumptions!" % smt.timestamp())
+                    report_tracked_assumptions("Conflicting assumptions:")
                     found_failed_assert = True
                     retstatus = "FAILED"
                     break
@@ -1823,7 +1890,7 @@ else:  # not tempind, covermode
     retstatus = "PASSED"
     while step < num_steps:
         smt_state(step)
-        smt_assert_consequent("(|%s_u| s%d)" % (topmod, step))
+        smt_assert_design_assumes(step)
         smt_assert_antecedent("(|%s_h| s%d)" % (topmod, step))
         smt_assert_consequent(get_constr_expr(constr_assumes, step))
 
@@ -1853,7 +1920,7 @@ else:  # not tempind, covermode
             if step+i < num_steps:
                 smt_state(step+i)
                 smt_assert_antecedent("(not (|%s_is| s%d))" % (topmod, step+i))
-                smt_assert_consequent("(|%s_u| s%d)" % (topmod, step+i))
+                smt_assert_design_assumes(step + i)
                 smt_assert_antecedent("(|%s_h| s%d)" % (topmod, step+i))
                 smt_assert_antecedent("(|%s_t| s%d s%d)" % (topmod, step+i-1, step+i))
                 smt_assert_consequent(get_constr_expr(constr_assumes, step+i))
@@ -1867,7 +1934,8 @@ else:  # not tempind, covermode
                     print_msg("Checking assumptions in steps %d to %d.." % (step, last_check_step))
 
                 if smt_check_sat() == "unsat":
-                    print("%s Assumptions are unsatisfiable!" % smt.timestamp())
+                    print_msg("Assumptions are unsatisfiable!")
+                    report_tracked_assumptions("Conficting assumptions:")
                     retstatus = "PREUNSAT"
                     break
 
@@ -1920,13 +1988,14 @@ else:  # not tempind, covermode
                                 print_msg("Appending additional step %d." % i)
                                 smt_state(i)
                                 smt_assert_antecedent("(not (|%s_is| s%d))" % (topmod, i))
-                                smt_assert_consequent("(|%s_u| s%d)" % (topmod, i))
+                                smt_assert_design_assumes(i)
                                 smt_assert_antecedent("(|%s_h| s%d)" % (topmod, i))
                                 smt_assert_antecedent("(|%s_t| s%d s%d)" % (topmod, i-1, i))
                                 smt_assert_consequent(get_constr_expr(constr_assumes, i))
                             print_msg("Re-solving with appended steps..")
                             if smt_check_sat() == "unsat":
-                                print("%s Cannot append steps without violating assumptions!" % smt.timestamp())
+                                print_msg("Cannot append steps without violating assumptions!")
+                                report_tracked_assumptions("Conflicting assumptions:")
                                 retstatus = "FAILED"
                                 break
                         print_anyconsts(step)

backends/smt2/smtbmc_incremental.py

@@ -15,6 +15,14 @@ class InteractiveError(Exception):
     pass
 
 
+def mkkey(data):
+    if isinstance(data, list):
+        return tuple(map(mkkey, data))
+    elif isinstance(data, dict):
+        raise InteractiveError(f"JSON objects found in assumption key: {data!r}")
+    return data
+
+
 class Incremental:
     def __init__(self):
         self.traceidx = 0
@@ -73,17 +81,17 @@ class Incremental:
 
         if min_len is not None and arg_len < min_len:
             if min_len == max_len:
-                raise (
+                raise InteractiveError(
                     f"{json.dumps(expr[0])} expression must have "
                     f"{min_len} argument{'s' if min_len != 1 else ''}"
                 )
             else:
-                raise (
+                raise InteractiveError(
                     f"{json.dumps(expr[0])} expression must have at least "
                     f"{min_len} argument{'s' if min_len != 1 else ''}"
                 )
         if max_len is not None and arg_len > max_len:
-            raise (
+            raise InteractiveError(
                 f"{json.dumps(expr[0])} expression can have at most "
                 f"{min_len} argument{'s' if max_len != 1 else ''}"
             )
@@ -96,14 +104,31 @@ class Incremental:
         smt_out.append(f"s{step}")
         return "module", smtbmc.topmod
 
-    def expr_mod_constraint(self, expr, smt_out):
+    def expr_cell(self, expr, smt_out):
-        self.expr_arg_len(expr, 1)
+        self.expr_arg_len(expr, 2)
         position = len(smt_out)
         smt_out.append(None)
-        arg_sort = self.expr(expr[1], smt_out, required_sort=["module", None])
+        arg_sort = self.expr(expr[2], smt_out, required_sort=["module", None])
+        smt_out.append(")")
         module = arg_sort[1]
+        cell = expr[1]
+        submod = smtbmc.smt.modinfo[module].cells.get(cell)
+        if submod is None:
+            raise InteractiveError(f"module {module!r} has no cell {cell!r}")
+        smt_out[position] = f"(|{module}_h {cell}| "
+        return ("module", submod)
+
+    def expr_mod_constraint(self, expr, smt_out):
         suffix = expr[0][3:]
-        smt_out[position] = f"(|{module}{suffix}| "
+        self.expr_arg_len(expr, 1, 2 if suffix in ["_a", "_u", "_c"] else 1)
+        position = len(smt_out)
+        smt_out.append(None)
+        arg_sort = self.expr(expr[-1], smt_out, required_sort=["module", None])
+        module = arg_sort[1]
+        if len(expr) == 3:
+            smt_out[position] = f"(|{module}{suffix} {expr[1]}| "
+        else:
+            smt_out[position] = f"(|{module}{suffix}| "
         smt_out.append(")")
         return "Bool"
 
@@ -223,20 +248,19 @@ class Incremental:
         subexpr = expr[2]
 
         if not isinstance(label, str):
-            raise InteractiveError(f"expression label has to be a string")
+            raise InteractiveError("expression label has to be a string")
 
         smt_out.append("(! ")
-        smt_out.appedd(label)
-        smt_out.append(" ")
-
         sort = self.expr(subexpr, smt_out)
-
+        smt_out.append(" :named ")
+        smt_out.append(label)
         smt_out.append(")")
 
         return sort
 
     expr_handlers = {
         "step": expr_step,
+        "cell": expr_cell,
         "mod_h": expr_mod_constraint,
         "mod_is": expr_mod_constraint,
         "mod_i": expr_mod_constraint,
@@ -302,6 +326,30 @@ class Incremental:
 
         assert_fn(self.expr_smt(cmd.get("expr"), "Bool"))
 
+    def cmd_assert_design_assumes(self, cmd):
+        step = self.arg_step(cmd)
+        smtbmc.smt_assert_design_assumes(step)
+
+    def cmd_get_design_assume(self, cmd):
+        key = mkkey(cmd.get("key"))
+        return smtbmc.assume_enables.get(key)
+
+    def cmd_update_assumptions(self, cmd):
+        expr = cmd.get("expr")
+        key = cmd.get("key")
+
+
+        key = mkkey(key)
+
+        result = smtbmc.smt.smt2_assumptions.pop(key, None)
+        if expr is not None:
+            expr = self.expr_smt(expr, "Bool")
+            smtbmc.smt.smt2_assumptions[key] = expr
+        return result
+
+    def cmd_get_unsat_assumptions(self, cmd):
+        return smtbmc.smt.get_unsat_assumptions(minimize=bool(cmd.get('minimize')))
+
     def cmd_push(self, cmd):
         smtbmc.smt_push()
 
@@ -313,11 +361,14 @@ class Incremental:
 
     def cmd_smtlib(self, cmd):
         command = cmd.get("command")
+        response = cmd.get("response", False)
         if not isinstance(command, str):
             raise InteractiveError(
                 f"raw SMT-LIB command must be a string, found {json.dumps(command)}"
             )
         smtbmc.smt.write(command)
+        if response:
+            return smtbmc.smt.read()
 
     def cmd_design_hierwitness(self, cmd=None):
         allregs = (cmd is None) or bool(cmd.get("allreges", False))
@@ -369,6 +420,21 @@ class Incremental:
 
         return dict(last_step=last_step)
 
+    def cmd_modinfo(self, cmd):
+        fields = cmd.get("fields", [])
+
+        mod = cmd.get("mod")
+        if mod is None:
+            mod = smtbmc.topmod
+        modinfo = smtbmc.smt.modinfo.get(mod)
+        if modinfo is None:
+            return None
+
+        result = dict(name=mod)
+        for field in fields:
+            result[field] = getattr(modinfo, field, None)
+        return result
+
     def cmd_ping(self, cmd):
         return cmd
 
@@ -377,6 +443,10 @@ class Incremental:
         "assert": cmd_assert,
         "assert_antecedent": cmd_assert,
         "assert_consequent": cmd_assert,
+        "assert_design_assumes": cmd_assert_design_assumes,
+        "get_design_assume": cmd_get_design_assume,
+        "update_assumptions": cmd_update_assumptions,
+        "get_unsat_assumptions": cmd_get_unsat_assumptions,
         "push": cmd_push,
         "pop": cmd_pop,
         "check": cmd_check,
@@ -384,6 +454,7 @@ class Incremental:
         "design_hierwitness": cmd_design_hierwitness,
         "write_yw_trace": cmd_write_yw_trace,
         "read_yw_trace": cmd_read_yw_trace,
+        "modinfo": cmd_modinfo,
         "ping": cmd_ping,
     }
 

backends/smt2/smtio.py

@@ -114,6 +114,7 @@ class SmtModInfo:
         self.clocks = dict()
         self.cells = dict()
         self.asserts = dict()
+        self.assumes = dict()
         self.covers = dict()
         self.maximize = set()
         self.minimize = set()
@@ -141,6 +142,7 @@ class SmtIo:
         self.recheck = False
         self.smt2cache = [list()]
         self.smt2_options = dict()
+        self.smt2_assumptions = dict()
         self.p = None
         self.p_index = solvers_index
         solvers_index += 1
@@ -602,6 +604,12 @@ class SmtIo:
             else:
                 self.modinfo[self.curmod].covers["%s_c %s" % (self.curmod, fields[2])] = fields[3]
 
+        if fields[1] == "yosys-smt2-assume":
+            if len(fields) > 4:
+                self.modinfo[self.curmod].assumes["%s_u %s" % (self.curmod, fields[2])] = f'{fields[4]} ({fields[3]})'
+            else:
+                self.modinfo[self.curmod].assumes["%s_u %s" % (self.curmod, fields[2])] = fields[3]
+
         if fields[1] == "yosys-smt2-maximize":
             self.modinfo[self.curmod].maximize.add(fields[2])
 
@@ -785,8 +793,13 @@ class SmtIo:
         return stmt
 
     def check_sat(self, expected=["sat", "unsat", "unknown", "timeout", "interrupted"]):
+        if self.smt2_assumptions:
+            assume_exprs = " ".join(self.smt2_assumptions.values())
+            check_stmt = f"(check-sat-assuming ({assume_exprs}))"
+        else:
+            check_stmt = "(check-sat)"
         if self.debug_print:
-            print("> (check-sat)")
+            print(f"> {check_stmt}")
         if self.debug_file and not self.nocomments:
             print("; running check-sat..", file=self.debug_file)
             self.debug_file.flush()
@@ -800,7 +813,7 @@ class SmtIo:
                     for cache_stmt in cache_ctx:
                         self.p_write(cache_stmt + "\n", False)
 
-            self.p_write("(check-sat)\n", True)
+            self.p_write(f"{check_stmt}\n", True)
 
             if self.timeinfo:
                 i = 0
@@ -868,7 +881,7 @@ class SmtIo:
 
         if self.debug_file:
             print("(set-info :status %s)" % result, file=self.debug_file)
-            print("(check-sat)", file=self.debug_file)
+            print(check_stmt, file=self.debug_file)
             self.debug_file.flush()
 
         if result not in expected:
@@ -945,6 +958,48 @@ class SmtIo:
     def bv2int(self, v):
         return int(self.bv2bin(v), 2)
 
+    def get_raw_unsat_assumptions(self):
+        self.write("(get-unsat-assumptions)")
+        exprs = set(self.unparse(part) for part in self.parse(self.read()))
+        unsat_assumptions = []
+        for key, value in self.smt2_assumptions.items():
+            # normalize expression
+            value = self.unparse(self.parse(value))
+            if value in exprs:
+                exprs.remove(value)
+                unsat_assumptions.append(key)
+        return unsat_assumptions
+
+    def get_unsat_assumptions(self, minimize=False):
+        if not minimize:
+            return self.get_raw_unsat_assumptions()
+        required_assumptions = {}
+
+        while True:
+            candidate_assumptions = {}
+            for key in self.get_raw_unsat_assumptions():
+                if key not in required_assumptions:
+                    candidate_assumptions[key] = self.smt2_assumptions[key]
+
+            while candidate_assumptions:
+
+                candidate_key, candidate_assume = candidate_assumptions.popitem()
+
+                self.smt2_assumptions = {}
+                for key, assume in candidate_assumptions.items():
+                    self.smt2_assumptions[key] = assume
+                for key, assume in required_assumptions.items():
+                    self.smt2_assumptions[key] = assume
+                result = self.check_sat()
+
+                if result == 'unsat':
+                    candidate_assumptions = None
+                else:
+                    required_assumptions[candidate_key] = candidate_assume
+
+            if candidate_assumptions is not None:
+                return list(required_assumptions)
+
     def get(self, expr):
         self.write("(get-value (%s))" % (expr))
         return self.parse(self.read())[0][1]