[llvm] [RISCV] Tune flag for fast vrgather.vv (PR #124664)

[Craig Topper via llvm-commits]

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@@ -2845,10 +2845,19 @@ InstructionCost RISCVTargetLowering::getLMULCost(MVT VT) const {
 
 
 /// Return the cost of a vrgather.vv instruction for the type VT.  vrgather.vv
-/// is generally quadratic in the number of vreg implied by LMUL.  Note that
+/// may be quadratic in the number of vreg implied by LMUL, and is assumed to
+/// be by default.  VRGartherCostModel reflects available options.  Note that
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topperc wrote:

VRGarther -> VRGather

https://github.com/llvm/llvm-project/pull/124664