[ARM] Lower llvm.ctlz.i32 to a libcall when clz is not available.

The inline sequence is very long (about 70 bytes on Thumb1), so it's
not really a good idea to inline it, especially when optimizing for
size.

Differential Revision: https://reviews.llvm.org/D47917

llvm-svn: 340458

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 3c9316780b5..9ce7343c495 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -4262,6 +4262,21 @@ void SelectionDAGLegalize::ConvertNodeToLibcall(SDNode *Node) {
                                        RTLIB::MUL_I16, RTLIB::MUL_I32,
                                        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));
+      break;
+    case MVT::i64:
+      Results.push_back(ExpandLibCall(RTLIB::CTLZ_I64, Node, false));
+      break;
+    case MVT::i128:
+      Results.push_back(ExpandLibCall(RTLIB::CTLZ_I128, Node, false));
+      break;
+    }
+    break;
   }
 
   // Replace the original node with the legalized result.