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0b5fad68b2
One optimization simplify-cfg performs is the converting of switches to lookup tables if the switch has > 4 cases. This is done by: 1. Finding the max/min case value and calculating the switch case range. 2. Create a lookup table basic block. 3. Perform a check in the switch's BB to see if the input value is in the switch's case range. If the input value satisfies said predicate branch to the lookup table BB, otherwise branch to the switch's default destination BB using the default value as the result. The conditional check consists of subtracting the min case value of the table from any input iN value and then ensuring that said value is unsigned less than the size of the lookup table represented as an iN value. If the lookup table is a covered lookup table, the size of the table will be N which is 0 as an iN value. Thus the comparison will be an `icmp ult` of an iN value against 0 which is always false yielding the incorrect result. This patch fixes this problem by recognizing if we have a covered lookup table and if we do, unconditionally jumps to the lookup table BB since the covering property of the lookup table implies no input values could not be handled by said BB. rdar://15268442 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193045 91177308-0d34-0410-b5e6-96231b3b80d8
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