REGISTER ALLOCATION USING AN IMPROVED REGISTER CANDIDATE USAGE MATRIX

An improved register allocator is provided to the code generator of a compiler. The improved register allocator allocates registers using an improved register candidate usage matrix. The improved register candidate usage matrix comprises row entries, one for each register candidate. Each row entry comprises usage bits indicating at least whether its register candidate is live at the entries, in the bodies, and at the exits of the various basic blocks. The improved register allocator allocates registers by block, deriving interference information from the improved usage matrix. It then merges the register allocation introducing spill code at points where register candidates are split. As a result, a register can be allocated to two register candidates that are live in the same basic block as long as they are not both live at some point in the basic block, and at the same time, a register candidate can be spilled in one basic block and allocated a register in another basic block.