[clang] [llvm] [RISCV][P-ext] Add scalar multiply high intrinsics (PR #225561)

[Craig Topper via llvm-commits]

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@@ -17590,6 +17623,48 @@ void RISCVTargetLowering::ReplaceNodeResults(SDNode *N,
       Results.push_back(DAG.getExtractSubvector(DL, VT, Res, 0));
       return;
     }
+    case Intrinsic::riscv_mulh_i32:
+    case Intrinsic::riscv_mulhr_i32:
+    case Intrinsic::riscv_mulhu_u32:
+    case Intrinsic::riscv_mulhru_u32:
+    case Intrinsic::riscv_mulhsu_i32:
+    case Intrinsic::riscv_mulhrsu_i32: {
+      // RV64 has no scalar mulh instructions; reuse the packed pmulh.w
+      // family on the low words, whose element 0 is the scalar product.
+      MVT VT = N->getSimpleValueType(0);
+      if (!Subtarget.is64Bit() || VT != MVT::i32)
+        return;
+      unsigned Opc;
+      switch (IntNo) {
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topperc wrote:

This switch is duplicated. Should make a helper function?

https://github.com/llvm/llvm-project/pull/225561