http://bugs.python.org/issue2459 -- speed up loops

Python/peephole.c

 /* Peephole optimizations for bytecode compiler. */
 
 #include "Python.h"
 
 #include "Python-ast.h"
 #include "node.h"
 #include "pyarena.h"
 #include "ast.h"
 #include "code.h"
 #include "compile.h"
 #include "symtable.h"
 #include "opcode.h"
 
 #define GETARG(arr, i) ((int)((arr[i+2]<<8) + arr[i+1]))
 #define UNCONDITIONAL_JUMP(op)  (op==JUMP_ABSOLUTE || op==JUMP_FORWARD)
 #define CONDITIONAL_JUMP(op) (op==POP_JUMP_IF_FALSE || op==POP_JUMP_IF_TRUE \
         || op==JUMP_IF_FALSE_OR_POP || op==JUMP_IF_TRUE_OR_POP)
 #define ABSOLUTE_JUMP(op) (op==JUMP_ABSOLUTE || op==CONTINUE_LOOP \
+        || op==FOR_ITER \
         || op==POP_JUMP_IF_FALSE || op==POP_JUMP_IF_TRUE \
         || op==JUMP_IF_FALSE_OR_POP || op==JUMP_IF_TRUE_OR_POP)
 #define JUMPS_ON_TRUE(op) (op==POP_JUMP_IF_TRUE || op==JUMP_IF_TRUE_OR_POP)
 #define GETJUMPTGT(arr, i) (GETARG(arr,i) + (ABSOLUTE_JUMP(arr[i]) ? 0 : i+3))
 #define SETARG(arr, i, val) arr[i+2] = val>>8; arr[i+1] = val & 255
 #define CODESIZE(op)  (HAS_ARG(op) ? 3 : 1)
 #define ISBASICBLOCK(blocks, start, bytes) \
         (blocks[start]==blocks[start+bytes-1])
 
 /* Replace LOAD_CONST c1. LOAD_CONST c2 ... LOAD_CONST cn BUILD_TUPLE n
@@ skipping 578 matching lines @@
 
         /* Remove NOPs and fixup jump targets */
         for (i=0, h=0 ; i<codelen ; ) {
                 opcode = codestr[i];
                 switch (opcode) {
                         case NOP:
                                 i++;
                                 continue;
 
                         case JUMP_ABSOLUTE:
-                        case CONTINUE_LOOP:
                         case POP_JUMP_IF_FALSE:
                         case POP_JUMP_IF_TRUE:
                         case JUMP_IF_FALSE_OR_POP:
                         case JUMP_IF_TRUE_OR_POP:
+                        case CONTINUE_LOOP:
+                        case FOR_ITER:
                                 j = addrmap[GETARG(codestr, i)];
                                 SETARG(codestr, i, j);
                                 break;
 
-                        case FOR_ITER:
                         case JUMP_FORWARD:
                         case SETUP_LOOP:
                         case SETUP_EXCEPT:
                         case SETUP_FINALLY:
                                 j = addrmap[GETARG(codestr, i) + i + 3] - addrmap[i] - 3;
                                 SETARG(codestr, i, j);
                                 break;
                 }
                 adj = CODESIZE(opcode);
                 while (adj--)
@@ skipping 10 matching lines @@
  exitUnchanged:
         if (blocks != NULL)
                 PyMem_Free(blocks);
         if (addrmap != NULL)
                 PyMem_Free(addrmap);
         if (codestr != NULL)
                 PyMem_Free(codestr);
         Py_INCREF(code);
         return code;
 }