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From: Julian S. <js...@ac...> - 2012-12-21 09:24:37
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On Wednesday, December 19, 2012, John Reiser wrote: > > Constant folder: enable Sub32(x,0) ==> x. > > Beware. Processor status (flag bits) might change, and in "unexpected" > ways. The constant folder operates on the IR, which makes all architected state changes explicit -- there are no "under the table" semantics. If a ppc sub insn sets flag bits then that will have been translated into its own fragment of IR independent of the actual SUB. Hence IR expressions are denote pure values and we can transform them as such. J |