[llvm] [RISCV] Teach fillUpExtensionSupportForSplat to handle nxvXi64 VMV_V_X_VL on RV32. (PR #99251)

[Luke Lau via llvm-commits]

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@@ -14477,10 +14477,22 @@ struct NodeExtensionHelper {
     // widening opcode by splatting to smaller element size.
     unsigned EltBits = VT.getScalarSizeInBits();
     unsigned ScalarBits = Op.getValueSizeInBits();
-    // Make sure we're getting all element bits from the scalar register.
-    // FIXME: Support implicit sign extension of vmv.v.x?
-    if (ScalarBits < EltBits)
+    // Make sure we're not getting all bits from the element, we need special
+    // handling.
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lukel97 wrote:

If we're not getting all bits?

https://github.com/llvm/llvm-project/pull/99251