[clang] [llvm] [mlir] Remove the `x86_mmx` IR type. (PR #98505)

[Phoebe Wang via llvm-commits]

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@@ -57594,6 +57599,86 @@ static SDValue combinePDEP(SDNode *N, SelectionDAG &DAG,
   return SDValue();
 }
 
+// Fixup the MMX intrinsics' types: in IR they are expressed with <1 x i64>,
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phoebewang wrote:

Can we use `i64` instead of `<1 x i64>` given we don't care about the ABI?

https://github.com/llvm/llvm-project/pull/98505