[PATCH] D120648: [DAGCombine] fold (bswap(srl (bswap c), 8*x)) -> (shl c, 8*x)

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


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Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:9730
+    auto *ShAmt = dyn_cast<ConstantSDNode>(N0.getOperand(1));
+    if (ShAmt && ShAmt->getZExtValue() % 8 == 0) {
+      SDValue BSwap = N0->getOperand(0);
----------------
Where did we verify that calling getZExtValue() wouldn't assert if the shift was enormuously large. It would definitely be UB, but we can't guarantee it was folded yet.


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  https://reviews.llvm.org/D120648/new/

https://reviews.llvm.org/D120648