Initial attempt at introducing well-formedness checking for SSA

Follows the #3123 skeleton with additional checks in SSA_stept.

Author: Petr Bauch

src/cbmc/bmc.cpp

@@ -638,6 +638,10 @@ void bmct::perform_symbolic_execution(
   goto_symext::get_goto_functiont get_goto_function)
 {
   symex.symex_from_entry_point_of(get_goto_function, symex_symbol_table);
+  if(options.get_bool_option("validate-ssa-equation"))
+  {
+    symex.validate(ns, validation_modet::INVARIANT);
+  }
   INVARIANT(
     options.get_bool_option("paths") || path_storage.empty(),
     "Branch points were saved even though we should have been "

src/cbmc/cbmc_parse_options.cpp

@@ -395,6 +395,11 @@ void cbmc_parse_optionst::get_command_line_options(optionst &options)
       "symex-coverage-report",
       cmdline.get_value("symex-coverage-report"));
 
+  if(cmdline.isset("validate-ssa-equation"))
+  {
+    options.set_option("validate-ssa-equation", true);
+  }
+
   PARSE_OPTIONS_GOTO_TRACE(cmdline, options);
 }
 

src/goto-symex/goto_symex.h

@@ -518,6 +518,11 @@ class goto_symext
       "attempting to read remaining_vccs");
     return _remaining_vccs;
   }
+
+  void validate(const namespacet &ns, const validation_modet vm) const
+  {
+    target.validate(ns, vm);
+  }
 };
 
 #endif // CPROVER_GOTO_SYMEX_GOTO_SYMEX_H

src/goto-symex/symex_target_equation.cpp

@@ -974,3 +974,57 @@ void symex_target_equationt::SSA_stept::output(std::ostream &out) const
 
   out << "Guard: " << format(guard) << '\n';
 }
+
+/// Check that the SSA step is well-formed
+/// \param ns namespace to lookup identifiers
+/// \param vm validation mode to be used for reporting failures
+void symex_target_equationt::SSA_stept::validate(
+  const namespacet &ns,
+  const validation_modet vm) const
+{
+  validate_full_expr(guard, ns, vm);
+
+  switch(type)
+  {
+  case goto_trace_stept::typet::ASSERT:
+  case goto_trace_stept::typet::ASSUME:
+  case goto_trace_stept::typet::GOTO:
+  case goto_trace_stept::typet::CONSTRAINT:
+    validate_full_expr(cond_expr, ns, vm);
+    break;
+  case goto_trace_stept::typet::ASSIGNMENT:
+  case goto_trace_stept::typet::DECL:
+    validate_full_expr(ssa_lhs, ns, vm);
+    validate_full_expr(ssa_full_lhs, ns, vm);
+    validate_full_expr(original_full_lhs, ns, vm);
+    validate_full_expr(ssa_rhs, ns, vm);
+    base_type_eq(ssa_lhs.get_original_expr(), ssa_rhs, ns);
+    break;
+  case goto_trace_stept::typet::INPUT:
+  case goto_trace_stept::typet::OUTPUT:
+    for(const auto &expr : io_args)
+      validate_full_expr(expr, ns, vm);
+    break;
+  case goto_trace_stept::typet::FUNCTION_CALL:
+    for(const auto &expr : ssa_function_arguments)
+      validate_full_expr(expr, ns, vm);
+  case goto_trace_stept::typet::FUNCTION_RETURN:
+  {
+    const symbolt *symbol;
+    DATA_CHECK(
+      called_function.empty() || !ns.lookup(called_function, symbol),
+      "unknown function identifier " + id2string(called_function));
+  }
+  break;
+  case goto_trace_stept::typet::NONE:
+  case goto_trace_stept::typet::LOCATION:
+  case goto_trace_stept::typet::DEAD:
+  case goto_trace_stept::typet::SHARED_READ:
+  case goto_trace_stept::typet::SHARED_WRITE:
+  case goto_trace_stept::typet::SPAWN:
+  case goto_trace_stept::typet::MEMORY_BARRIER:
+  case goto_trace_stept::typet::ATOMIC_BEGIN:
+  case goto_trace_stept::typet::ATOMIC_END:
+    break;
+  }
+}

src/goto-symex/symex_target_equation.h

@@ -267,6 +267,8 @@ class symex_target_equationt:public symex_targett
       std::ostream &out) const;
 
     void output(std::ostream &out) const;
+
+    void validate(const namespacet &ns, const validation_modet vm) const;
   };
 
   std::size_t count_assertions() const
@@ -323,6 +325,12 @@ class symex_target_equationt:public symex_targett
     return false;
   }
 
+  void validate(const namespacet &ns, const validation_modet vm) const
+  {
+    for(const SSA_stept &step : SSA_steps)
+      step.validate(ns, vm);
+  }
+
 protected:
   // for enforcing sharing in the expressions stored
   merge_irept merge_irep;

src/util/ssa_expr.h

@@ -139,6 +139,25 @@ class ssa_exprt:public symbol_exprt
   /* Used to determine whether or not an identifier can be built
    * before trying and getting an exception */
   static bool can_build_identifier(const exprt &src);
+
+  static void check(
+    const exprt &expr,
+    const validation_modet vm = validation_modet::INVARIANT)
+  {
+    DATA_CHECK(!expr.has_operands(), "SSA expression should not have operands");
+    DATA_CHECK(expr.id() == ID_symbol, "SSA expression symbols are symbols");
+    DATA_CHECK(expr.get_bool(ID_C_SSA_symbol), "wrong SSA expression ID");
+  }
+
+  static void validate(
+    const exprt &expr,
+    const namespacet &ns,
+    const validation_modet vm = validation_modet::INVARIANT)
+  {
+    check(expr, vm);
+    validate_full_expr(
+      static_cast<const exprt &>(expr.find(ID_expression)), ns, vm);
+  }
 };
 
 /*! \brief Cast a generic exprt to an \ref ssa_exprt

src/util/validate_expressions.cpp

@@ -15,6 +15,7 @@ Author: Daniel Poetzl
 
 #include "expr.h"
 #include "namespace.h"
+#include "ssa_expr.h"
 #include "std_expr.h"
 #include "validate.h"
 
@@ -32,6 +33,10 @@ void call_on_expr(const exprt &expr, Args &&... args)
   {
     CALL_ON_EXPR(plus_exprt);
   }
+  else if(expr.get_bool(ID_C_SSA_symbol))
+  {
+    CALL_ON_EXPR(ssa_exprt);
+  }
   else
   {
 #ifdef REPORT_UNIMPLEMENTED_EXPRESSION_CHECKS

src/util/validation_interface.h

@@ -9,11 +9,16 @@ Author: Daniel Poetzl
 #ifndef CPROVER_UTIL_VALIDATION_INTERFACE_H
 #define CPROVER_UTIL_VALIDATION_INTERFACE_H
 
-#define OPT_VALIDATE "(validate-goto-model)"
+#define OPT_VALIDATE                                                           \
+  "(validate-goto-model)"                                                      \
+  "(validate-ssa-equation)"
 
 #define HELP_VALIDATE                                                          \
   " --validate-goto-model        enable additional well-formedness checks on " \
   "the\n"                                                                      \
-  "                              goto program\n"
+  "                              goto program\n"                               \
+  " --validate-ssa-equation      enable additional well-formedness checks on " \
+  "the\n"                                                                      \
+  "                              SSA representation\n"
 
 #endif /* CPROVER_UTIL_VALIDATION_INTERFACE_H */