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On x86, shifting a vector by a scalar is significantly cheaper than shifting a vector by another fully general vector. Unfortunately, because SelectionDAG operates on just one basic block at a time, the shufflevector instruction that reveals whether the right-hand side of a shift *is* really a scalar is often not visible to CodeGen when it's needed. This adds another handler to CodeGenPrepare, to sink any useful shufflevector instructions down to the basic block where they're used, predicated on a target hook (since on other architectures, doing so will often just introduce extra real work). rdar://problem/16063505 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201655 91177308-0d34-0410-b5e6-96231b3b80d8
Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for the Low Level Virtual Machine, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. Please see the documentation provided in docs/ for further assistance with LLVM, and in particular docs/GettingStarted.rst for getting started with LLVM and docs/README.txt for an overview of LLVM's documentation setup. If you're writing a package for LLVM, see docs/Packaging.rst for our suggestions.