Addressing Mode Selection in GCC

GCC has no formal addressing mode selection mechanism. It uses target hooks to generate valid addressing modes for a target. However, a significant amount of high level information is destroyed while doing this, especially for targets lacking a rich set of addressing modes. This leads to poor aliasing, and subsequently poorer CSE, GCSE, and scheduling. Hence, an unoptimal object code. This paper proposes an abstraction over RTL to generate machine independent addressing modes to achieve better aliasing. The actual addressing modes of the target are exposed after the first scheduling pass, where they are selected based on current execution scenario. Inter block address inheritance is also done at this point. The idea can be extended to specify a general “mid-level” RTL for GCC.