[SelectionDAG] Allow lowering CTPOP into a libcall

Some in-tree targets (e.g. ARM) could benefit from this lowering,
at least in opt-size mode, but I don't know if the libcall
is available in their libgcc, so no tests.

Author: s-barannikov

llvm/include/llvm/IR/RuntimeLibcalls.def

@@ -85,6 +85,9 @@ HANDLE_LIBCALL(NEG_I64, "__negdi2")
 HANDLE_LIBCALL(CTLZ_I32, "__clzsi2")
 HANDLE_LIBCALL(CTLZ_I64, "__clzdi2")
 HANDLE_LIBCALL(CTLZ_I128, "__clzti2")
+HANDLE_LIBCALL(CTPOP_I32, "__popcountsi2")
+HANDLE_LIBCALL(CTPOP_I64, "__popcountdi2")
+HANDLE_LIBCALL(CTPOP_I128, "__popcountti2")
 
 // Floating-point
 HANDLE_LIBCALL(ADD_F32, "__addsf3")

llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

@@ -140,12 +140,9 @@ class SelectionDAGLegalize {
                        RTLIB::Libcall Call_F128,
                        RTLIB::Libcall Call_PPCF128,
                        SmallVectorImpl<SDValue> &Results);
-  SDValue ExpandIntLibCall(SDNode *Node, bool isSigned,
-                           RTLIB::Libcall Call_I8,
-                           RTLIB::Libcall Call_I16,
-                           RTLIB::Libcall Call_I32,
-                           RTLIB::Libcall Call_I64,
-                           RTLIB::Libcall Call_I128);
+  SDValue ExpandIntLibCall(SDNode *Node, bool IsSigned, RTLIB::Libcall Call_I8,
+                           RTLIB::Libcall Call_I16, RTLIB::Libcall Call_I32,
+                           RTLIB::Libcall Call_I64, RTLIB::Libcall Call_I128);
   void ExpandArgFPLibCall(SDNode *Node,
                           RTLIB::Libcall Call_F32, RTLIB::Libcall Call_F64,
                           RTLIB::Libcall Call_F80, RTLIB::Libcall Call_F128,
@@ -2209,7 +2206,7 @@ void SelectionDAGLegalize::ExpandFPLibCall(SDNode* Node,
   ExpandFPLibCall(Node, LC, Results);
 }
 
-SDValue SelectionDAGLegalize::ExpandIntLibCall(SDNode* Node, bool isSigned,
+SDValue SelectionDAGLegalize::ExpandIntLibCall(SDNode *Node, bool IsSigned,
                                                RTLIB::Libcall Call_I8,
                                                RTLIB::Libcall Call_I16,
                                                RTLIB::Libcall Call_I32,
@@ -2224,7 +2221,9 @@ SDValue SelectionDAGLegalize::ExpandIntLibCall(SDNode* Node, bool isSigned,
   case MVT::i64:  LC = Call_I64; break;
   case MVT::i128: LC = Call_I128; break;
   }
-  return ExpandLibCall(LC, Node, isSigned).first;
+  assert(LC != RTLIB::UNKNOWN_LIBCALL &&
+         "LibCall explicitly requested, but not available");
+  return ExpandLibCall(LC, Node, IsSigned).first;
 }
 
 /// Expand the node to a libcall based on first argument type (for instance
@@ -4980,19 +4979,20 @@ void SelectionDAGLegalize::ConvertNodeToLibcall(SDNode *Node) {
                                        RTLIB::MUL_I64, RTLIB::MUL_I128));
     break;
   case ISD::CTLZ_ZERO_UNDEF:
-    switch (Node->getSimpleValueType(0).SimpleTy) {
-    default:
-      llvm_unreachable("LibCall explicitly requested, but not available");
-    case MVT::i32:
-      Results.push_back(ExpandLibCall(RTLIB::CTLZ_I32, Node, false).first);
-      break;
-    case MVT::i64:
-      Results.push_back(ExpandLibCall(RTLIB::CTLZ_I64, Node, false).first);
-      break;
-    case MVT::i128:
-      Results.push_back(ExpandLibCall(RTLIB::CTLZ_I128, Node, false).first);
-      break;
-    }
+    Results.push_back(ExpandIntLibCall(Node, /*IsSigned=*/false,
+                                       RTLIB::UNKNOWN_LIBCALL,
+                                       RTLIB::UNKNOWN_LIBCALL,
+                                       RTLIB::CTLZ_I32,
+                                       RTLIB::CTLZ_I64,
+                                       RTLIB::CTLZ_I128));
+    break;
+  case ISD::CTPOP:
+    Results.push_back(ExpandIntLibCall(Node, /*IsSigned=*/false,
+                                       RTLIB::UNKNOWN_LIBCALL,
+                                       RTLIB::UNKNOWN_LIBCALL,
+                                       RTLIB::CTPOP_I32,
+                                       RTLIB::CTPOP_I64,
+                                       RTLIB::CTPOP_I128));
     break;
   case ISD::RESET_FPENV: {
     // It is legalized to call 'fesetenv(FE_DFL_ENV)'. On most targets