[PATCH] D39230: [IndVarSimplify] Do not expand unsafe expressions in IndVarSimplify

[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/Transforms/Scalar/IndVarSimplify.cpp:1589
+  // have division by value which is potentially zero.
+  if (!isSafeToExpand(AddRec, *SE))
+    return nullptr;
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Hm, I'm not sold on this.  If `AR` is expandable (which we know since we got it from a PHI in the IR, right?) `sext(AR)` and `zext(AR)` should also be expandable.


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Comment at: test/Transforms/IndVarSimplify/2017-10-24_unsafe_division.ll:39
+  %iv.trunc = trunc i64 %iv to i32
+  %unsafe = udiv i32 224, %iv.trunc
+  br label %inner_loop
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I'm not sure if I understand this test case - if `%iv.trunc` is `0` then doesn't the function already divide by `0` (and thus have UB, making any transformation correct by definition)?


https://reviews.llvm.org/D39230