[PATCH] D138873: [InstCombine] canonicalize trunc + insert as bitcast + shuffle, part 2

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon accepted this revision.
RKSimon added a comment.
This revision is now accepted and ready to land.

LGTM



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Comment at: llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp:1554
+    // Check the shift amount to see if this can be folded to a select-shuffle.
+    // Big endian has MSB at vector index 0, so the insert index is flipped.
+    if (IsBigEndian && (NumEltsInScalar - 1 - IndexC) * VecEltWidth != ShiftC)
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Make it clear that we only allow an 'identity' shuffle mask here


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