[clang] [llvm] [PowerPC] Fix behavior of rldimi/rlwimi/rlwnm builtins (PR #85040)

[Chen Zheng via cfe-commits]

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@@ -10764,30 +10764,53 @@ SDValue PPCTargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
     return DAG.getRegister(PPC::R2, MVT::i32);
 
   case Intrinsic::ppc_rldimi: {
+    assert(Subtarget.isPPC64() && "rldimi is only available in 64-bit!");
+    if (Op.getConstantOperandVal(4) == 0)
+      return Op.getOperand(2);
     uint64_t SH = Op.getConstantOperandVal(3);
     unsigned MB = 0, ME = 0;
-    if (!isRunOfOnes64(Op.getConstantOperandVal(4), MB, ME) || ME != 63 - SH)
+    if (!isRunOfOnes64(Op.getConstantOperandVal(4), MB, ME))
       report_fatal_error("invalid rldimi mask!");
-    return SDValue(DAG.getMachineNode(
-                       PPC::RLDIMI, dl, MVT::i64,
-                       {Op.getOperand(1), Op.getOperand(2), Op.getOperand(3),
-                        DAG.getTargetConstant(MB, dl, MVT::i32)}),
-                   0);
+
+    // For all-one mask, MB will be set to 0, adjust it next to 63-SH.
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chenzheng1030 wrote:

For all-one mask, to improve the readability, is it better to just return the `Intrinsic::ppc_rldimi` as `ISD::ROTL (Op.getOperand(1), Op.getOperand(3))`?

I think this would also benefit later optimizations as we are using a ISD node here.

https://github.com/llvm/llvm-project/pull/85040