[PATCH] D39231: [SCEV][NFC] Assert that we do not expand something unsafe

[Sanjoy Das via Phabricator via llvm-commits]

sanjoy requested changes to this revision.
sanjoy added inline comments.
This revision now requires changes to proceed.


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Comment at: lib/Analysis/ScalarEvolutionExpander.cpp:1749
 
+  assert(isSafeToExpand(S, SE) && "Attempt to expand something unsafe!");
   SCEVInsertPointGuard Guard(Builder, this);
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I think this is overtly conservative.  Expanding something unsafe is a problem only if "unsafety" (in practice, today this is just division by zero) was not present in the IR before.  For instance if we have `%v = udiv i32 %x, %y` in the IR then it is perfectly fine to `getSCEV` on `%v` and then re-expand it before or after `%v` since if `%y` was `0` then the program is undefined.


https://reviews.llvm.org/D39231