[llvm] [RISCV][CostModel] Estimate cost of Extract/InsertElement with non-constant index when vector instructions are not available (PR #67334)

[Philip Reames via llvm-commits]

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@@ -1460,8 +1460,29 @@ InstructionCost RISCVTTIImpl::getVectorInstrCost(unsigned Opcode, Type *Val,
   std::pair<InstructionCost, MVT> LT = getTypeLegalizationCost(Val);
 
   // This type is legalized to a scalar type.
-  if (!LT.second.isVector())
-    return 0;
+  if (!LT.second.isVector()) {
+    auto *FixedVecTy = dyn_cast<FixedVectorType>(Val);
+    // Scalable vectors can't be legalized with scalars, return invalid cost.
+    if (!FixedVecTy)
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preames wrote:

Does this bit actually get hit?  I'd have expected it to go through the  if (LT.second.isScalableVector() && !LT.first.isValid()) check just below.  

https://github.com/llvm/llvm-project/pull/67334