Index: lld/COFF/Driver.cpp
===================================================================
--- lld/COFF/Driver.cpp
+++ lld/COFF/Driver.cpp
@@ -966,6 +966,10 @@
   for (auto *Arg : Args.filtered(OPT_merge))
     parseMerge(Arg->getValue());
 
+  // Add default section merging rules after user rules. User rules take
+  // precedence, but we will emit a warning if there is a conflict.
+  parseMerge(".xdata=.rdata");
+
   // Handle /section
   for (auto *Arg : Args.filtered(OPT_section))
     parseSection(Arg->getValue());
Index: lld/test/COFF/icf-xdata.s
===================================================================
--- lld/test/COFF/icf-xdata.s
+++ lld/test/COFF/icf-xdata.s
@@ -1,13 +1,23 @@
 # RUN: llvm-mc %s -triple x86_64-windows-msvc -filetype=obj -o %t.obj
+# RUN: lld-link %t.obj -dll -noentry -out:%t.dll -merge:.xdata=.xdata 2>&1 \
+# RUN:     | FileCheck %s --check-prefix=WARN
+# RUN: llvm-readobj -sections %t.dll | FileCheck %s --check-prefix=XDATA
 # RUN: lld-link %t.obj -dll -noentry -out:%t.dll
-# RUN: llvm-readobj -sections %t.dll | FileCheck %s
+# RUN: llvm-readobj -sections %t.dll | FileCheck %s --check-prefix=RDATA
 
 # There shouldn't be much xdata, because all three .pdata entries (12 bytes
 # each) should use the same .xdata unwind info.
-# CHECK:         Name: .pdata
-# CHECK-NEXT:    VirtualSize: 0x24
-# CHECK:         Name: .xdata
-# CHECK-NEXT:    VirtualSize: 0x8
+# XDATA:         Name: .pdata
+# XDATA-NEXT:    VirtualSize: 0x24
+# XDATA:         Name: .xdata
+# XDATA-NEXT:    VirtualSize: 0x8
+#
+# WARN: warning: .xdata=.rdata: already merged into .xdata
+#
+# RDATA:         Name: .pdata
+# RDATA-NEXT:    VirtualSize: 0x24
+# RDATA:         Name: .rdata
+# RDATA-NEXT:    VirtualSize: 0x8
 
 	.text
 callee: