CRPC-TR93306  --  abstract, keywords



SIMD architectures offer an alternative to MIMD architectures for 
obtaining high performance computation through parallelism.
However, to obtain the best performance on such architectures,
aggressive compilation techniques are required. One issue that SIMD
compilers must address is generating code to change the machine
context; i.e., disabling processors not involved in the current
computation. This paper addresses the cost of changing the machine
context. 

We present two compiler optimizations that reduce the cost of context
changes. The first optimization, context partitioning, reorders the
code so that as subgrid loops are generated, as many statements as
possible that require the same context are placed in the same loop
nest. The second optimization, context splitting, splits the iteration 
space of the subgrid loops into sets that have invariant contexts.
This allows us to hoist the code that sets the machine context out of
the subgrid loops. 


Keywords: SIMD compilation, context changes, loop fusion, loop splitting