[llvm] [RISCV][ISel] Combine vector fadd/fsub/fmul with fp extend. (PR #81248)

[Wang Pengcheng via llvm-commits]

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@@ -13313,41 +13334,57 @@ struct NodeExtensionHelper {
   /// Helper function to get the narrow type for \p Root.
   /// The narrow type is the type of \p Root where we divided the size of each
   /// element by 2. E.g., if Root's type <2xi16> -> narrow type <2xi8>.
-  /// \pre The size of the type of the elements of Root must be a multiple of 2
-  /// and be greater than 16.
-  static MVT getNarrowType(const SDNode *Root) {
+  /// \pre Both the narrow type and the original type should be legal.
+  static MVT getNarrowType(const SDNode *Root, ExtKind SupportsExt) {
     MVT VT = Root->getSimpleValueType(0);
 
     // Determine the narrow size.
     unsigned NarrowSize = VT.getScalarSizeInBits() / 2;
-    assert(NarrowSize >= 8 && "Trying to extend something we can't represent");
-    MVT NarrowVT = MVT::getVectorVT(MVT::getIntegerVT(NarrowSize),
-                                    VT.getVectorElementCount());
+
+    unsigned NarrowMinSize = SupportsExt == ExtKind::FPExt ? 16 : 8;
+
+    MVT EltVT = SupportsExt == ExtKind::FPExt
+                    ? MVT::getFloatingPointVT(NarrowSize)
+                    : MVT::getIntegerVT(NarrowSize);
+
+    assert(NarrowSize >= NarrowMinSize &&
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wangpc-pp wrote:

Can we inline `NarrowMinSize` to here as this is the only usage (and it's in assertion).

https://github.com/llvm/llvm-project/pull/81248