[PATCH] D120933: [SDAG] match rotate pattern with extra 'or' operation

[Sanjay Patel via Phabricator via llvm-commits]

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This is another fold generalized from D111530 <https://reviews.llvm.org/D111530>. We can find a common source for a rotate operation hidden inside an 'or':
https://alive2.llvm.org/ce/z/9pV8hn

Deciding when this is profitable vs. a funnel-shift is tricky, but this does not show any regressions: if a target has a rotate but it does not have a funnel-shift, then try to form the rotate here. That is why we don't have x86 test diffs for the scalar tests that are duplicated from AArch64 ( 74a65e3834d9487 <https://reviews.llvm.org/rG74a65e3834d9487a3030ce48ef1022db11a01dfb> ) - shld/shrd are available. That also makes it difficult to show vector diffs - the only case where I found a diff was on x86 AVX512 or XOP with i64 elements.

There's an additional check for a legal type to avoid a problem seen with x86-32 where we form a 64-bit rotate but then it gets split inefficiently. We might avoid that by adding more rotate folds, but I didn't check to see what is missing on that path.

This gets most of the motivating patterns for AArch64 / ARM that are in D111530 <https://reviews.llvm.org/D111530>. We still need a couple of enhancements to setcc pattern matching with rotate/funnel-shift to get the rest.


https://reviews.llvm.org/D120933

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/AArch64/icmp-shift-opt.ll
  llvm/test/CodeGen/AArch64/logic-shift.ll
  llvm/test/CodeGen/ARM/consthoist-icmpimm.ll
  llvm/test/CodeGen/ARM/icmp-shift-opt.ll
  llvm/test/CodeGen/X86/rotate_vec.ll

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