[PATCH] D62990: [SCEV]When safe, compute MinStart as unsigned_min(Start - Stride) + Stride in computeMaxBECountForLT

[Eli Friedman via Phabricator via llvm-commits]

efriedma added subscribers: reames, nikic.
efriedma added a comment.

I think this is sound now.

Could you add some test coverage for the cases we don't and/or can't transform?  Maybe also a test where "end" is known-positive, but not constant.



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Comment at: lib/Analysis/ScalarEvolution.cpp:10491
+  // exit:
+  //   ret void
+  //
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Probably easier to understand the C form of the loop, at first glance: `for (unsigned i = start; i < 17; i += 8) { [...] }`


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Comment at: lib/Analysis/ScalarEvolution.cpp:10504
+    MinStart = getUnsignedRangeMin(S) +
+               dyn_cast<SCEVConstant>(Stride)->getAPInt();
+
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`cast<>`


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Comment at: test/Analysis/ScalarEvolution/2008-11-18-Stride2.ll:8
 ; This is a tricky testcase for unsigned wrap detection which ScalarEvolution
 ; doesn't yet know how to do.
 
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