[PATCH] D71657: [SDAG] Handle BUILD_PAIR in ComputeNumSignBits

[Craig Topper via Phabricator via llvm-commits]

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


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Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:3461
+  case ISD::BUILD_PAIR:
+    Tmp = ComputeNumSignBits(Op.getOperand(1), Depth + 1);
+    if (Op.getOperand(1).getValueSizeInBits() == Tmp)
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I don't think this is correct. If the first call returns "all sign bits" then we check operand(0) that call will always return at least 1. So we increase the total by at least 1. So its impossible for this code to ever return that the number of sign bits of a build_pair is exactly half the total size of the build_pair. That seems wrong.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D71657/new/

https://reviews.llvm.org/D71657