Index: lld/trunk/COFF/Driver.cpp
===================================================================
--- lld/trunk/COFF/Driver.cpp
+++ lld/trunk/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/trunk/test/COFF/icf-xdata.s
===================================================================
--- lld/trunk/test/COFF/icf-xdata.s
+++ lld/trunk/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:
Index: lld/trunk/test/COFF/pdb.test
===================================================================
--- lld/trunk/test/COFF/pdb.test
+++ lld/trunk/test/COFF/pdb.test
@@ -201,7 +201,7 @@
 RAW-NEXT:            virtual size
 RAW-NEXT:       1000 virtual address
 RAW-NEXT:        200 size of raw data
-RAW-NEXT:        400 file pointer to raw data
+RAW-NEXT:        200 file pointer to raw data
 RAW-NEXT:          0 file pointer to relocation table
 RAW-NEXT:          0 file pointer to line numbers
 RAW-NEXT:          0 number of relocations
@@ -214,7 +214,7 @@
 RAW-NEXT:            virtual size
 RAW-NEXT:       2000 virtual address
 RAW-NEXT:        200 size of raw data
-RAW-NEXT:        600 file pointer to raw data
+RAW-NEXT:        400 file pointer to raw data
 RAW-NEXT:          0 file pointer to relocation table
 RAW-NEXT:          0 file pointer to line numbers
 RAW-NEXT:          0 number of relocations
@@ -224,24 +224,11 @@
 RAW-NEXT:            IMAGE_SCN_MEM_EXECUTE
 RAW-NEXT:            IMAGE_SCN_MEM_READ
 RAW:        SECTION HEADER #3
-RAW-NEXT:     .xdata name
-RAW-NEXT:            virtual size
-RAW-NEXT:       3000 virtual address
-RAW-NEXT:        200 size of raw data
-RAW-NEXT:        800 file pointer to raw data
-RAW-NEXT:          0 file pointer to relocation table
-RAW-NEXT:          0 file pointer to line numbers
-RAW-NEXT:          0 number of relocations
-RAW-NEXT:          0 number of line numbers
-RAW-NEXT:   40000040 flags
-RAW-NEXT:            IMAGE_SCN_CNT_INITIALIZED_DATA
-RAW-NEXT:            IMAGE_SCN_MEM_READ
-RAW:        SECTION HEADER #4
 RAW-NEXT:     .rdata name
 RAW-NEXT:            virtual size
-RAW-NEXT:       4000 virtual address
+RAW-NEXT:       3000 virtual address
 RAW-NEXT:        200 size of raw data
-RAW-NEXT:        A00 file pointer to raw data
+RAW-NEXT:        600 file pointer to raw data
 RAW-NEXT:          0 file pointer to relocation table
 RAW-NEXT:          0 file pointer to line numbers
 RAW-NEXT:          0 number of relocations
@@ -249,6 +236,7 @@
 RAW-NEXT:   40000040 flags
 RAW-NEXT:            IMAGE_SCN_CNT_INITIALIZED_DATA
 RAW-NEXT:            IMAGE_SCN_MEM_READ
+RAW-NOT:        SECTION HEADER
 RAW:                        Original Section Headers
 RAW-NEXT: ============================================================
 RAW-NEXT:   PDB does not contain the requested image section header type
@@ -262,8 +250,13 @@
 RAW-NEXT:   SC[.text]   | mod = 1, 0002:0016, size = 6, data crc = 2139436471, reloc crc = 0
 RAW-NEXT:                 IMAGE_SCN_CNT_CODE | IMAGE_SCN_ALIGN_16BYTES | IMAGE_SCN_MEM_EXECUTE |
 RAW-NEXT:                 IMAGE_SCN_MEM_READ
-RAW-NEXT:   SC[.xdata]  | mod = 0, 0003:0000, size = 8, data crc = 264583633, reloc crc = 0
+RAW-NEXT:   SC[???]     | mod = 0, 0003:0000, size = 8, data crc = 264583633, reloc crc = 0
 RAW-NEXT:                 IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_ALIGN_4BYTES | IMAGE_SCN_MEM_READ
+RAW-NEXT:   SC[???]     | mod = 2, 0003:0008, size = 28, data crc = 0, reloc crc = 0
+RAW-NEXT:                 IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ
+RAW-NEXT:   SC[???]     | mod = 2, 0003:0036, size = 94, data crc = 0, reloc crc = 0
+RAW-NEXT:                 IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ
+RAW-NOT: SC[
 RAW:                             Section Map
 RAW-NEXT: ============================================================
 RAW-NEXT:   Section 0000 | ovl = 0, group = 0, frame = 1, name = 65535
@@ -277,7 +270,4 @@
 RAW-NEXT:                  flags = read | 32 bit addr | selector
 RAW-NEXT:   Section 0003 | ovl = 0, group = 0, frame = 4, name = 65535
 RAW-NEXT:                  class = 65535, offset = 0, size =
-RAW-NEXT:                  flags = read | 32 bit addr | selector
-RAW-NEXT:   Section 0004 | ovl = 0, group = 0, frame = 5, name = 65535
-RAW-NEXT:                  class = 65535, offset = 0, size =
 RAW-NEXT:                  flags = 32 bit addr | absolute addr