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64-bit integer division in Intel CPUs is extremely slow, much slower than 32-bit division. On the other hand, 8-bit and 16-bit divisions aren't any faster. The only important exception is Atom where DIV8 is fastest. Because of that, the patch 1) Enables bypassing of 64-bit division for Atom, Silvermont and all big cores. 2) Modifies 64-bit bypassing to use 32-bit division instead of 16-bit one. This doesn't make the shorter division slower but increases chances of taking it. Moreover, it's much more likely to prove at compile-time that a value fits 32 bits and doesn't require a run-time check (e.g. zext i32 to i64). Differential Revision: https://reviews.llvm.org/D28196 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291800 91177308-0d34-0410-b5e6-96231b3b80d8