Abstract: A method and device for optimizing a compiler involves cooperation between the global and local register allocators in assigning symbolic registers to hardware registers. A large procedure may have many associated symbolic registers; the invention involves partitioning the symbolic registers into at least two portions, and allowing the global register allocator to assign one portion and the local register allocator to assign another portion. The registers may be partitioned based on different criteria, such as local vs. global registers, or spill costs, or shallow vs. nested regions.

Abstract: A method and apparatus for coloring an interference graph eliminates register copy instructions in an instruction stream by taking into consideration the colors of a node's direct or transitive partners when choosing a color for a node. By assigning a color to a node that is also the color of a direct or transitive partner, register copy instructions between the two partners may be eliminated. If more than one of the partners at any given level are colored, one of the colors may be selected over the others using an appropriate heuristic, such as a scheme that weights the colors appropriately.

Abstract: A method and apparatus allows a compiler to optimize code in the presence of exception handlers. According to a first embodiment, arcs are added to a control flow graph, prior to performing global optimizations, to account for exception handling code. According to the second embodiment, information relating to control flow to exception handlers is provided in pseudo-references in the code, which allows the compiler to determine how to appropriately optimize the code.

Abstract: A method and apparatus for coloring an interference graph yields a higher number of colored nodes by taking into consideration the colors of neighbors of a node's uncolored constrained neighbors. By assigning a color to a node that is also the color of a neighbor of an uncolored constrained neighbor, one color constraint is removed, increasing the probability of coloring the uncolored constrained neighbor. If more than one of the neighbors of the uncolored constrained neighbors are colored, one of the colors may be selected over the others using an appropriate heuristic.

Abstract: A method and apparatus for truncating runaway lifetimes of program variables calculates liveness for each variable based on upwardly exposed uses. Reaching definitions are then calculated for at least the program variables that have runaway lifetimes. The liveness information is compared to the reaching definition information to determine whether a variable that is live upon entry to a basic block has a definition that reaches the end of each predecessor block, or has a use within the basic block. If the reaching definition for a variable reaches the beginning of the block and if there is a predecessor block for which there is no reaching definition, the variable has a runaway lifetime. The variable also has a runaway lifetime if there is a use of the variable in a block without a reaching definition for the variable at the beginning of the block. The runaway lifetime is truncated by inserting an instruction such as a pseudo-definition of the variable into the instruction stream at an appropriate place.