[clang] [llvm] [RISCV] Added the MIPS prefetch extensions for MIPS RV64 P8700. (PR #145647)

[Min-Yih Hsu via cfe-commits]

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@@ -2925,6 +2925,49 @@ bool RISCVDAGToDAGISel::SelectAddrRegImm(SDValue Addr, SDValue &Base,
   return true;
 }
 
+/// Similar to SelectAddrRegImm, except that the offset restricted for
+/// unsinged nine bits.
+bool RISCVDAGToDAGISel::SelectAddrRegImm9(SDValue Addr, SDValue &Base,
+                                          SDValue &Offset) {
+  if (SelectAddrFrameIndex(Addr, Base, Offset))
+    return true;
+
+  SDLoc DL(Addr);
+  MVT VT = Addr.getSimpleValueType();
+
+  if (CurDAG->isBaseWithConstantOffset(Addr)) {
+    int64_t CVal = cast<ConstantSDNode>(Addr.getOperand(1))->getSExtValue();
+    if (isUInt<9>(CVal)) {
+      Base = Addr.getOperand(0);
+
+      if (auto *FIN = dyn_cast<FrameIndexSDNode>(Base))
+        Base = CurDAG->getTargetFrameIndex(FIN->getIndex(), VT);
+      Offset = CurDAG->getSignedTargetConstant(CVal, DL, VT);
+      return true;
+    }
+
+    // Handle with 12 bit offset with sign bit off with ADDI.
+    // For Immediate Range [0, 2047]
+    else if (Addr.getOpcode() == ISD::ADD &&
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mshockwave wrote:

nit: sorry this just looks a bit odd, could you move the comment into the `else if` body and move `else if` up to line 2947

https://github.com/llvm/llvm-project/pull/145647