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9e75857c92
When optimizing for size, a loop is vectorized only if the resulting vector loop completely replaces the original scalar loop. This holds if no runtime guards are needed, if the original trip-count TC does not overflow, and if TC is a known constant that is a multiple of the VF. The last two TC-related conditions can be overcome by 1. rounding the trip-count of the vector loop up from TC to a multiple of VF; 2. masking the vector body under a newly introduced "if (i <= TC-1)" condition. The patch allows loops with arbitrary trip counts to be vectorized under -Os, subject to the existing cost model considerations. It also applies to loops with small trip counts (under -O2) which are currently handled as if under -Os. The patch does not handle loops with reductions, live-outs, or w/o a primary induction variable, and disallows interleave groups. (Third, final and main part of -) Differential Revision: https://reviews.llvm.org/D50480 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@344743 91177308-0d34-0410-b5e6-96231b3b80d8