Hi Aran, > Where are the SSE instructions defined? Specifically, I > cannot find the def for ADDSDrr. take a look at X86InstrSSE.td, lines 1,472 and 1,425 ff. ADDSDrr is defined as part of a multiclass [1] record, that's why simple grep'ing doesn't work. :-) Christoph [1] http://llvm.org/docs/TableGenFundamentals.html#multiclass