refinement for __builtin_constant_p

git-svn-id: svn+ssh://svn.cprover.org/srv/svn/cbmc/trunk@2818 6afb6bc1-c8e4-404c-8f48-9ae832c5b171

regression/ansi-c/gcc_builtin_constant_p1/main.c

@@ -0,0 +1,29 @@
+#include <assert.h>
+
+enum { E1=1 } var;
+
+struct whatnot
+{
+} whatnot_var;
+
+int main()
+{
+  // this is gcc only
+
+  #ifdef __GNUC__
+  assert(__builtin_constant_p("some string"));
+  assert(__builtin_constant_p(1.0f));
+  assert(__builtin_constant_p(E1));
+  assert(!__builtin_constant_p(var));
+  assert(!__builtin_constant_p(main));
+  assert(!__builtin_constant_p(whatnot_var));
+  assert(!__builtin_constant_p(&var));
+  assert(__builtin_constant_p(__builtin_constant_p(var)));
+
+  // side-effects are _not_ evaluated
+  int i=0;
+  assert(!__builtin_constant_p(i++));
+  assert(i==0);
+  #endif
+}
+

regression/ansi-c/gcc_builtin_constant_p1/test.desc

@@ -0,0 +1,8 @@
+CORE
+main.c
+
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring
+^CONVERSION ERROR$

src/ansi-c/c_typecheck_expr.cpp

@@ -2398,8 +2398,25 @@ void c_typecheck_baset::do_special_functions(
       // try to produce constant
       exprt tmp1=expr.arguments().front();
       simplify(tmp1, *this);
-
-      exprt tmp2=from_integer(tmp1.is_constant(), expr.type());      
+      
+      bool is_constant=false;
+      
+      // Need to do some special treatment for string literals,
+      // which are (void *)&("lit"[0])
+      if(tmp1.id()==ID_typecast &&
+         tmp1.operands().size()==1 &&
+         tmp1.op0().id()==ID_address_of &&
+         tmp1.op0().operands().size()==1 &&
+         tmp1.op0().op0().id()==ID_index &&
+         tmp1.op0().op0().operands().size()==2 &&
+         tmp1.op0().op0().op0().id()==ID_string_constant)
+      {
+        is_constant=true;
+      }
+      else
+        is_constant=tmp1.is_constant();
+      
+      exprt tmp2=from_integer(is_constant, expr.type());
       tmp2.location()=location;
       expr.swap(tmp2);
     }

src/ansi-c/gcc_builtin_headers_generic.h

@@ -4,7 +4,7 @@ void __builtin_va_end(void *ap);
 void __builtin_va_copy(__builtin_va_list dest, __builtin_va_list src);
 void *__builtin_va_arg_pack();
 int __builtin_va_arg_pack_len();
-int __builtin_constant_p(int);
+int __builtin_constant_p();
 int __builtin_abs(int);
 long int __builtin_labs(long);
 double __builtin_cos(double);