Method and apparatus for creating alternative versions of code segments and dynamically substituting execution of the alternative code versions

Abstract

Method and apparatus for creating alternative versions of code segments and dynamically substituting execution of the alternative code versions. Checkpoints in program code are identified by a compiler, and the checkpoints are used to delineate segments of object code. Two sets of segments of object code are generated, where the first and second sets of object code segments are optimized at different levels. In one embodiment, the first set of segments is optimized at a greater level than the second set of segments. Upon detecting a program error in executing the first set of segments, state information of the program is recovered from a checkpoint, and an object code module is selected from either the first set or second set for execution.

What is claimed is:  
     
         1 . A computer-implemented method for compiling program code, comprising: 
 generating first object code segments optimized at a first optimization level;    generating second object code segments optimized at a second optimization level, wherein the second object code segments are respectively associated with the first object code segments;    checkpoints in the program code, the checkpoints delineating the object code segments; and    generating checkpoint code for execution at the checkpoints, wherein the checkpoint code saves state information of the program.    
     
     
         2 . The method of  claim 1 , wherein the second optimization level includes no optimizations.  
     
     
         3 . The method of  claim 2 , wherein the first optimization level includes more optimizations than the second optimization level.  
     
     
         4 . The method of  claim 1 , wherein the first optimization level includes more optimizations than the second optimization level.  
     
     
         5 . The method of  claim 1 , further comprising undoing optimizations made in generating the first object code segments in generating the second object code segments.  
     
     
         6 . The method of  claim 5 , further comprising: 
 identifying checkpoints in the program code, the checkpoints delineating the object code segments; and    generating checkpoint code for execution at the checkpoints, wherein the checkpoint code saves state information of the program.    
     
     
         7 . The method of  claim 1 , further comprising: 
 generating segments of intermediate code;    for each segment of intermediate code, 
 optimizing the segment of intermediate code in generating a corresponding one of the first object code segments; and  
 undoing optimizations of intermediate code in generating a corresponding one of the second object code segments.  
   
     
     
         8 . The method of  claim 7 , further comprising: 
 identifying checkpoints in the program code, the checkpoints delineating the object code segments; and    generating checkpoint code for execution at the checkpoints, wherein the checkpoint code saves state information of the program.    
     
     
         9 . The method of  claim 1 , further comprising: 
 identifying checkpoints in the program code, the checkpoints delineating the object code segments; and    generating checkpoint code for execution at the checkpoints, wherein the checkpoint code saves state information of the program.    
     
     
         10 . The method of  claim 9 , wherein the second optimization level includes no optimizations.  
     
     
         11 . The method of  claim 10 , wherein the first optimization level includes more optimizations than the second optimization level.  
     
     
         12 . The method of  claim 9 , wherein the first optimization level includes more optimizations than the second optimization level.  
     
     
         13 . A computer-implemented method for recovery from a program execution error, comprising: 
 identifying checkpoints in the program code;    generating checkpoint code for execution at the checkpoints, wherein the checkpoint code saves state information of the program;    generating first object code segments optimized at a first optimization level, the object code segments delineated by the checkpoints;    generating second object code segments optimized at a second optimization level, wherein the second object code segments are respectively associated with the first object code segments;    upon detecting a program error, recovering state information of the program from a checkpoint; and    selecting for execution between a first and second object code segment associated with the checkpoint of the recovering step.    
     
     
         14 . The method of  claim 13 , wherein the first optimization level includes more optimizations than the second optimization level, and further comprising: 
 initially executing the first object code segments; and    retrying execution of a first object code segment associated with the checkpoint from the recovering step before selecting a second object code segment for execution.    
     
     
         15 . The method of  claim 13 , wherein the second optimization level includes no optimizations.  
     
     
         16 . The method of  claim 15 , wherein the first optimization level includes more optimizations than the second optimization level.  
     
     
         17 . The method of  claim 13 , wherein the first optimization level includes more optimizations than the second optimization level.  
     
     
         18 . The method of  claim 13 , further comprising undoing optimizations made in generating the first object code segments in generating the second object code segments.  
     
     
         19 . An apparatus for compiling program code, comprising: 
 means for generating first object code segments optimized at a first optimization level;    means for generating second object code segments optimized at a second optimization level, wherein the second object code segments are respectively associated with the first object code segments;    means for identifying checkpoints in the program code, the checkpoints delineating the object code segments; and    means for generating checkpoint code for execution at the checkpoints, wherein the checkpoint code saves state information of the program.    
     
     
         20 . An apparatus for recovery from a program execution error, comprising: 
 means for identifying checkpoints in the program code;    means for generating checkpoint code for execution at the checkpoints, wherein the checkpoint code saves state information of the program;    means for generating first object code segments optimized at a first optimization level, the object code segments delineated by the checkpoints;    means for generating second object code segments optimized at a second optimization level, wherein the second object code segments are respectively associated with the first object code segments;    means for upon detecting a program error, recovering state information of the program from a checkpoint; and    means for selecting for execution between a first and second object code segment associated with the checkpoint of the recovering step.    
     
     
         21 . A computer program product configured for causing a computer to perform the steps of: 
 generating first object code segments optimized at a first optimization level;    generating second object code segments optimized at a second optimization level, wherein the second object code segments are respectively associated with the first object code segments;    identifying checkpoints in the program code, the checkpoints delineating the object code segments; and    generating checkpoint code for execution at the checkpoints, wherein the checkpoint code saves state information of the program.    
     
     
         22 . A computer-implemented method for compiling program code, comprising: 
 generating during compilation of the program code first machine code segments optimized at a first optimization level; and    generating during compilation of the program code second machine code segments optimized at a second optimization level, wherein the second machine code segments are respectively associated with the first machine code segments.    
     
     
         23 . The method of  claim 22 , wherein the second optimization level includes no optimizations.  
     
     
         24 . The method of  claim 23 , wherein the first optimization level includes more optimizations than the second optimization level.  
     
     
         25 . The method of  claim 22 , wherein the first optimization level includes more optimizations than the second optimization level.  
     
     
         26 . The method of  claim 22 , further comprising undoing optimizations made in generating the first machine code segments in generating the second machine code segments.  
     
     
         27 . The method of  claim 26 , further comprising: 
 identifying checkpoints in the program code, the checkpoints delineating the object code segments; and    generating checkpoint code for execution at the checkpoints, wherein the checkpoint code saves state information of the program.    
     
     
         28 . The method of  claim 22 , further comprising: 
 generating segments of intermediate code;    for each segment of intermediate code, 
 optimizing the segment of intermediate code in generating a corresponding one of the first machine code segments; and  
 undoing optimizations of intermediate code in generating a corresponding one of the second machine code segments.  
   
     
     
         29 . An apparatus for compiling program code, comprising: 
 means for generating during compilation of the program code first machine code segments optimized at a first optimization level; and    means for generating during compilation of the program code second machine code segments optimized at a second optimization level, wherein the second machine code segments are respectively associated with the first machine code segments.    
     
     
         30 . An article of manufacture, comprising: 
 a computer-readable medium configured with instructions for causing a processor-based arrangement to perform the steps of,    generating during compilation of the program code first machine code segments optimized at a first optimization level; and    generating during compilation of the program code second machine code segments optimized at a second optimization level, wherein the second machine code segments are respectively associated with the first machine code segments.