Proposal for SentinelInputRange

[Timon Gehr]

On 02/28/2013 10:40 PM, Walter Bright wrote:
> On 2/28/2013 9:05 AM, deadalnix wrote:
>> I see nothing that can't be done by an optimizing compiler. Maybe
>> something is,
>> but I can't find it. And the example you pointed me aren't.
>
> Tell me how front() will be optimized out to this.
>
>              case '>':
>                  p++;
>                  if (*p == '=')
>                  {   p++;
>                      t->value = TOKge;                   // >=
>                  }
>                  else if (*p == '>')
>                  {   p++;
>                      if (*p == '=')
>                      {   p++;
>                          t->value = TOKshrass;           // >>=
>                      }
>                      else if (*p == '>')
>                      {   p++;
>                          if (*p == '=')
>                          {   p++;
>                              t->value = TOKushrass;      // >>>=
>                          }
>                          else
>                              t->value = TOKushr;         // >>>
>                      }
>                      else
>                          t->value = TOKshr;              // >>
>                  }
>                  else
>                      t->value = TOKgt;                   // >
>                  return;


I'd be surprised if DMD couldn't do it already.

assume: popFront(){ p++; }, front()=>*p, empty()=>*p=='\0'

     case '>':
         popFront();
         if(!empty && front == '='){
             popFront();
             t->value = TOKge;                   // >=
         }else if(!empty && front == '>'){
             popFront();
             if(!empty && front == '='){
                 popFront();
                 t->value = TOKshrass;           // >>=
             }else if(!empty && front == '>'){
                 popFront();
                 if(!empty && front == '='){
                     popFront();
                     t->value = TOKushrass;      // >>>=
                 }else t->value = TOKushr;       // >>>
             }else t->value = TOKshr;            // >>
         }else t->value = TOKgt;                 // >
         return;

     // inlining =>

     case '>':
         p++;
         if(!(*p=='\0') && *p == '='){
             p++;
             t->value = TOKge;                   // >=
         }else if(!(*p=='\0') && *p == '>'){
             p++;
             if(!(*p=='\0') && *p == '='){
                 p++;
                 t->value = TOKshrass;           // >>=
             }else if(!(*p=='\0') && *p == '>'){
                 p++;
                 if(!(*p=='\0') && *p == '='){
                     p++;
                     t->value = TOKushrass;      // >>>=
                 }else t->value = TOKushr;       // >>>
             }else t->value = TOKshr;            // >>
         }else t->value = TOKgt;                 // >
         return;

     // expression simplification
     // (eg. trivial peephole for x!=a && x==b case sufficient)
     // =>

     case '>':
         p++;
         if(*p == '='){
             p++;
             t->value = TOKge;                   // >=
         }else if(*p == '>'){
             p++;
             if(*p == '='){
                 p++;
                 t->value = TOKshrass;           // >>=
             }else if(*p == '>'){
                 p++;
                 if(*p == '='){
                     p++;
                     t->value = TOKushrass;      // >>>=
                 }else t->value = TOKushr;       // >>>
             }else t->value = TOKshr;            // >>
         }else t->value = TOKgt;                 // >
         return;