implementation for __builtin_bswap at compile time, issue #202

Author: Daniel Kroening

regression/ansi-c/gcc_builtins1/main.c

@@ -1,14 +1,17 @@
 #ifdef __GNUC__
 
-enum { E1 = __builtin_isinf(1.0) };
-enum { E2 = __builtin_isnan(1.0) };
-enum { E3 = __builtin_isinf(__builtin_inf()) };
-enum { E4 = __builtin_signbit(-1.0) };
-enum { E5 = __builtin_classify_type(1) };
-enum { E6 = sizeof(int) };
-enum { E7 = __alignof__(int) };
-enum { E8 = (int)1.0 };
-enum { E9 = __builtin_popcount(123) };
+enum { E01 = __builtin_isinf(1.0) };
+enum { E02 = __builtin_isnan(1.0) };
+enum { E03 = __builtin_isinf(__builtin_inf()) };
+enum { E04 = __builtin_signbit(-1.0) }; // clang doesn't do this one
+enum { E05 = __builtin_classify_type(1) };
+enum { E06 = sizeof(int) };
+enum { E07 = __alignof__(int) };
+enum { E08 = (int)1.0 };
+enum { E09 = __builtin_popcount(123) };
+enum { E10 = __builtin_bswap16(0xaabb) };
+enum { E11 = __builtin_bswap32(0xaabb) };
+enum { E12 = __builtin_bswap64(0xaabb) };
 
 #endif
 

src/ansi-c/c_typecheck_expr.cpp

@@ -2480,6 +2480,25 @@ exprt c_typecheck_baset::do_special_functions(
 
     return pointer_object_expr;
   }
+  else if(identifier=="__builtin_bswap16" ||
+          identifier=="__builtin_bswap32" ||
+          identifier=="__builtin_bswap64")
+  {
+    typecheck_function_call_arguments(expr);
+
+    if(expr.arguments().size()!=1)
+    {
+      err_location(f_op);
+      error() << identifier << " expects one operand" << eom;
+      throw 0;
+    }
+    
+    exprt bswap_expr(ID_bswap, expr.type());
+    bswap_expr.operands()=expr.arguments();
+    bswap_expr.add_source_location()=source_location;
+    
+    return bswap_expr;
+  }
   else if(identifier==CPROVER_PREFIX "isnanf" || 
           identifier==CPROVER_PREFIX "isnand" ||
           identifier==CPROVER_PREFIX "isnanld" ||

src/ansi-c/expr2c.cpp

@@ -4401,6 +4401,9 @@ std::string expr2ct::convert(
   else if(src.id()==ID_isinf)
     return convert_function(src, "isinf", precedence=16);
 
+  else if(src.id()==ID_bswap)
+    return convert_function(src, "bswap", precedence=16);
+
   else if(src.id()==ID_isnormal)
     return convert_function(src, "isnormal", precedence=16);
 

src/ansi-c/gcc_builtin_headers_generic.h

@@ -154,17 +154,17 @@ int __builtin_parityl(unsigned long);
 int __builtin_parityll(unsigned long long);
 void __builtin_trap(void);
 void __builtin___clear_cache(char *begin, char *end);
-int __builtin_clz(unsigned int x);
+int __builtin_clz(unsigned int);
 int __builtin_clzll(unsigned long long);
-int __builtin_ctz(unsigned int x);
+int __builtin_ctz(unsigned int);
 int __builtin_ctzll(unsigned long long);
-int __builtin_parity(unsigned int x);
+int __builtin_parity(unsigned int);
 int __builtin_ffsl(unsigned long);
 int __builtin_clzl(unsigned long);
 int __builtin_ctzl(unsigned long);
-short int __builtin_bswap16(short int x);
-long int __builtin_bswap32(long int x);
-long long int __builtin_bswap64(long long int x);
+short unsigned int __builtin_bswap16(short unsigned int);
+long unsigned int __builtin_bswap32(long unsigned int);
+long long unsigned int __builtin_bswap64(long long unsigned int);
 int __builtin_classify_type();
 int __builtin_isinf(double);
 int __builtin_isinff(float);

src/util/irep_ids.txt

@@ -732,3 +732,4 @@ verilog_unsigned_vector
 verilog_array
 low
 high
+bswap

src/util/simplify_expr.cpp

@@ -2549,6 +2549,8 @@ bool simplify_exprt::simplify_node(exprt &expr)
   else if(expr.id()==ID_ieee_float_equal ||
           expr.id()==ID_ieee_float_notequal)
     result=simplify_ieee_float_relation(expr) && result;
+  else if(expr.id()==ID_bswap)
+    result=simplify_bswap(expr) && result;
   else if(expr.id()==ID_isinf)
     result=simplify_isinf(expr) && result;
   else if(expr.id()==ID_isnan)

src/util/simplify_expr_class.h

@@ -100,6 +100,7 @@ class simplify_exprt
   bool simplify_dereference(exprt &expr);
   bool simplify_address_of(exprt &expr);
   bool simplify_pointer_offset(exprt &expr);
+  bool simplify_bswap(exprt &expr);
   bool simplify_isinf(exprt &expr);
   bool simplify_isnan(exprt &expr);
   bool simplify_isnormal(exprt &expr);

src/util/simplify_expr_int.cpp

@@ -23,6 +23,50 @@ Author: Daniel Kroening, [email protected]
 
 /*******************************************************************\
 
+Function: simplify_exprt::simplify_bswap
+
+  Inputs:
+
+ Outputs:
+
+ Purpose:
+
+\*******************************************************************/
+
+bool simplify_exprt::simplify_bswap(exprt &expr)
+{
+  if(expr.type().id()==ID_unsignedbv &&
+     expr.operands().size()==1 &&
+     expr.op0().type()==expr.type() &&
+     expr.op0().is_constant())
+  {
+    std::size_t width=to_bitvector_type(expr.type()).get_width();
+    mp_integer value;
+    to_integer(expr.op0(), value);
+    std::vector<mp_integer> bytes;
+
+    // take apart
+    for(std::size_t bit=0; bit<width; bit+=8)
+      bytes.push_back((value>>bit)%256);
+      
+    // put back together, but backwards
+    mp_integer new_value=0;
+    for(std::size_t bit=0; bit<width; bit+=8)
+    {
+      assert(!bytes.empty());
+      new_value+=bytes.back()<<bit;
+      bytes.pop_back();
+    }
+    
+    expr=from_integer(new_value, expr.type());
+    return false;
+  }
+  
+  return true;
+}
+
+/*******************************************************************\
+
 Function: simplify_exprt::simplify_mult
 
   Inputs: