[PATCH] D47681: [DAGCombiner] Bug 31275- Extract a shift from a constant mul or udiv if a rotate can be formed

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


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Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:5057
 // a rot[lr].
 SDNode *DAGCombiner::MatchRotate(SDValue LHS, SDValue RHS, const SDLoc &DL) {
   // Must be a legal type.  Expanded 'n promoted things won't work with rotates.
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Is this always considered worth doing,
or the check whether this should be done is on the caller's side?


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Comment at: test/CodeGen/X86/rotate-extract.ll:2
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown | FileCheck %s
+
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You could also copy this into `test/CodeGen/AArch64/rotate-extract.ll`,
since that should also profit from the transform.


https://reviews.llvm.org/D47681