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This causes a regression in CodeGen/PowerPC/select_const.ll (at least in the no isel case).
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A trunc can change the value of the shift amount, so how is it correct to peek through it?
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Yes, we're going to need a KnownBits check to ensure we were truncating away known zero bits
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Check the truncate doesn't lose information.
Remove the zero extent case as it seems to only regress things.
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | ||
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13184–13185 | Please can you move this as an NFC pre-commit and then rebase the patch? Just to show that there are no changes to the logic in isTruncateOf. |
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | ||
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2500 | if (Known.countMaxActiveBits() < Sel.getScalarValueSizeInBits()) or so? |