[PATCH] D130895: [RISCV] Make VL choosing for a splat-like VMV based on its users

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


================
Comment at: llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp:2548
+  // Check whether VL operands are the same. Return common non-constant VL.
+  SDValue VL = getVLOperand(*Range.begin(), TII);
+  if (all_of(drop_begin(Range),
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craig.topper wrote:
> I don't think you can assume the using instruction VL is relative to the same SEW/LMUL as the splat. There could have been a bitcast between them that changed the element size. Bitcasts don't generate code. I think insert_subvector/extract_subvector can also change the type without creating any code. Mainly for fractional LMULs.
You'll need to extract the SEW and LMUL from both instructions and make sure they are in the same ratio so they would have the same VLMax.


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  https://reviews.llvm.org/D130895/new/

https://reviews.llvm.org/D130895