[PATCH] D109786: [SCEV] (udiv X, Y) * Y is always NUW

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:2403
+      Ops.size() == 2) {
+    auto *UDiv = dyn_cast<SCEVUDivExpr>(Ops[0]);
+    if (UDiv && UDiv->getNumOperands() == 2 && UDiv->getOperand(1) == Ops[1])
----------------
I think this only covers a subset of cases because it assumes the udiv is the first operand. Due to complexity sorting, this is a given for the case where `Y` is SCEVUnknown, but wouldn't we want this to trigger also for something like `3 * (udiv X, 3)`?


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Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:2404
+    auto *UDiv = dyn_cast<SCEVUDivExpr>(Ops[0]);
+    if (UDiv && UDiv->getNumOperands() == 2 && UDiv->getOperand(1) == Ops[1])
+      Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
----------------
I believe UDiv always has two operands, multi operand udiv isn't well-defined...


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https://reviews.llvm.org/D109786