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When unsafe FP math operations are enabled, we can use the fre[s] and frsqrte[s] instructions, which generate reciprocal (sqrt) estimates, together with some Newton iteration, in order to quickly generate floating-point division and sqrt results. All of these instructions are separately optional, and so each has its own feature flag (except for the Altivec instructions, which are covered under the existing Altivec flag). Doing this is not only faster than using the IEEE-compliant fdiv/fsqrt instructions, but allows these computations to be pipelined with other computations in order to hide their overall latency. I've also added a couple of missing fnmsub patterns which turned out to be missing (but are necessary for good code generation of the Newton iterations). Altivec needs a similar fix, but that will probably be more complicated because fneg is expanded for Altivec's v4f32. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178617 91177308-0d34-0410-b5e6-96231b3b80d8
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