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appropriate unit tests. This change in itself is not expected to affect any functionality at this point, but it will serve as a stepping stone to improve FileCheck's variable matching capabilities. Luckily, our regex implementation already supports backreferences, although a bit of hacking is required to enable it. It supports both Basic Regular Expressions (BREs) and Extended Regular Expressions (EREs), without supporting backrefs for EREs, following POSIX strictly in this respect. And EREs is what we actually use (rightly). This is contrary to many implementations (including the default on Linux) of POSIX regexes, that do allow backrefs in EREs. Adding backref support to our EREs is a very simple change in the regcomp parsing code. I fail to think of significant cases where it would clash with existing things, and can bring more versatility to the regexes we write. There's always the danger of a backref in a specially crafted regex causing exponential matching times, but since we mainly use them for testing purposes I don't think it's a big problem. [it can also be placed behind a flag specific to FileCheck, if needed]. For more details, see: * http://lists.cs.uiuc.edu/pipermail/llvmdev/2012-November/055840.html * http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20121126/156878.html git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168802 91177308-0d34-0410-b5e6-96231b3b80d8
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