[llvm] [RISCV] Add codegen support for Zvfbfmin (PR #87911)

[Jianjian Guan via llvm-commits]

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@@ -1080,6 +1080,21 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
       }
     }
 
+    // TODO: Could we merge some code with zvfhmin?
+    if (Subtarget.hasVInstructionsBF16()) {
+      for (MVT VT : BF16VecVTs) {
+        if (!isTypeLegal(VT))
+          continue;
+        setOperationAction({ISD::FP_ROUND, ISD::FP_EXTEND}, VT, Custom);
+        setOperationAction({ISD::VP_FP_ROUND, ISD::VP_FP_EXTEND}, VT, Custom);
+        setOperationAction({ISD::CONCAT_VECTORS, ISD::INSERT_SUBVECTOR,
+                            ISD::EXTRACT_SUBVECTOR, ISD::SCALAR_TO_VECTOR},
+                           VT, Custom);
+        setOperationAction({ISD::LOAD, ISD::STORE}, VT, Custom);
+        // TODO: Promote to fp32.
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jacquesguan wrote:

`SPLAT_VECTOR` and select/merge with splat depends on `Zvfh`, so I plan to add these in a separate patch.

https://github.com/llvm/llvm-project/pull/87911