[llvm] [RISCV] Fold FP32->BF16->FP32 (PR #69687)

[Craig Topper via llvm-commits]

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@@ -2158,6 +2158,16 @@ void RISCVDAGToDAGISel::Select(SDNode *Node) {
     }
     break;
   }
+  case RISCVISD::FP_EXTEND_BF16: {
+    SDValue V = Node->getOperand(0);
+    // fold (fp_extend_bf16 (fp_round_bf16 op)) -> op
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topperc wrote:

Why is this legal? bf16 has less mantissa bits than f32.

https://github.com/llvm/llvm-project/pull/69687