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4781d8ee1c
Fixes PR13371: indvars pass incorrectly substitutes 'undef' values. I do not like this fix. It's needed until/unless the meaning of undef changes. It attempts to be complete according to the IR spec, but I don't have much confidence in the implementation given the difficulty testing undefined behavior. Worse, this invalidates some of my hard-fought work on indvars and LSR to optimize pointer induction variables. It results benchmark regressions, which I'll track internally. On x86_64 no LTO I see: -3% huffbench -3% 400.perlbench -8% fhourstones My only suggestion for recovering is to change the meaning of undef. If we could trust an arbitrary instruction to produce a some real value that can be manipulated (e.g. incremented) according to non-undef rules, then this case could be easily handled with SCEV. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160421 91177308-0d34-0410-b5e6-96231b3b80d8
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