[Mips] Fix cttz.i32 fails to lower on mips16 (#179633)

MIPS16 cannot handle constant pools created by CTTZ table lookup
expansion. This causes "Cannot select" errors when trying to select
MipsISD::Lo nodes for constant pool addresses.
    
Modify the table lookup conditions to check ConstantPool operation
status, and only set ConstantPool to Custom in non-MIPS16 mode in MIPS
backend.
    
This ensures MIPS16 uses the ISD::CTPOP instead of attempting
unsupported constant pool operations.

Fix #61055.

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index fd71cd846ed5..99968baec98e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -9620,9 +9620,13 @@ SDValue TargetLowering::CTTZTableLookup(SDNode *Node, SelectionDAG &DAG,
                                         unsigned BitWidth) const {
   if (BitWidth != 32 && BitWidth != 64)
     return SDValue();
+
+  const DataLayout &TD = DAG.getDataLayout();
+  if (!isOperationCustom(ISD::ConstantPool, getPointerTy(TD)))
+    return SDValue();
+
   APInt DeBruijn = BitWidth == 32 ? APInt(32, 0x077CB531U)
                                   : APInt(64, 0x0218A392CD3D5DBFULL);
-  const DataLayout &TD = DAG.getDataLayout();
   MachinePointerInfo PtrInfo =
       MachinePointerInfo::getConstantPool(DAG.getMachineFunction());
   unsigned ShiftAmt = BitWidth - Log2_32(BitWidth);