diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -102,7 +102,7 @@
 
 // Default filename used for profile generation.
 std::string getDefaultProfileGenName() {
-  return DebugInfoCorrelate ? "default_%p.proflite" : "default_%m.profraw";
+  return DebugInfoCorrelate ? "default_%m.proflite" : "default_%m.profraw";
 }
 
 class EmitAssemblyHelper {
diff --git a/compiler-rt/lib/profile/InstrProfilingMerge.c b/compiler-rt/lib/profile/InstrProfilingMerge.c
--- a/compiler-rt/lib/profile/InstrProfilingMerge.c
+++ b/compiler-rt/lib/profile/InstrProfilingMerge.c
@@ -47,7 +47,6 @@
 COMPILER_RT_VISIBILITY
 int __llvm_profile_check_compatibility(const char *ProfileData,
                                        uint64_t ProfileSize) {
-  /* Check profile header only for now  */
   __llvm_profile_header *Header = (__llvm_profile_header *)ProfileData;
   __llvm_profile_data *SrcDataStart, *SrcDataEnd, *SrcData, *DstData;
   SrcDataStart =
@@ -102,13 +101,6 @@
 COMPILER_RT_VISIBILITY
 int __llvm_profile_merge_from_buffer(const char *ProfileData,
                                      uint64_t ProfileSize) {
-  if (__llvm_profile_get_version() & VARIANT_MASK_DBG_CORRELATE) {
-    PROF_ERR(
-        "%s\n",
-        "Debug info correlation does not support profile merging at runtime. "
-        "Instead, merge raw profiles using the llvm-profdata tool.");
-    return 1;
-  }
   if (__llvm_profile_get_version() & VARIANT_MASK_TEMPORAL_PROF) {
     PROF_ERR("%s\n",
              "Temporal profiles do not support profile merging at runtime. "
@@ -118,7 +110,8 @@
 
   __llvm_profile_data *SrcDataStart, *SrcDataEnd, *SrcData, *DstData;
   __llvm_profile_header *Header = (__llvm_profile_header *)ProfileData;
-  char *SrcCountersStart;
+  char *SrcCountersStart, *DstCounter;
+  const char *SrcCountersEnd, *SrcCounter;
   const char *SrcNameStart;
   const char *SrcValueProfDataStart, *SrcValueProfData;
   uintptr_t CountersDelta = Header->CountersDelta;
@@ -128,14 +121,32 @@
                               Header->BinaryIdsSize);
   SrcDataEnd = SrcDataStart + Header->NumData;
   SrcCountersStart = (char *)SrcDataEnd;
-  SrcNameStart = SrcCountersStart +
-                 Header->NumCounters * __llvm_profile_counter_entry_size();
+  SrcCountersEnd = SrcCountersStart +
+                   Header->NumCounters * __llvm_profile_counter_entry_size();
+  SrcNameStart = SrcCountersEnd;
   SrcValueProfDataStart =
       SrcNameStart + Header->NamesSize +
       __llvm_profile_get_num_padding_bytes(Header->NamesSize);
   if (SrcNameStart < SrcCountersStart)
     return 1;
 
+  // Merge counters by iterating the entire counter section when debug info
+  // correlation is enabled.
+  if (__llvm_profile_get_version() & VARIANT_MASK_DBG_CORRELATE) {
+    for (SrcCounter = SrcCountersStart,
+        DstCounter = __llvm_profile_begin_counters();
+         SrcCounter < SrcCountersEnd;) {
+      if (__llvm_profile_get_version() & VARIANT_MASK_BYTE_COVERAGE) {
+        *DstCounter &= *SrcCounter;
+      } else {
+        *(uint64_t *)DstCounter += *(uint64_t *)SrcCounter;
+      }
+      SrcCounter += __llvm_profile_counter_entry_size();
+      DstCounter += __llvm_profile_counter_entry_size();
+    }
+    return 0;
+  }
+
   for (SrcData = SrcDataStart,
       DstData = (__llvm_profile_data *)__llvm_profile_begin_data(),
       SrcValueProfData = SrcValueProfDataStart;
diff --git a/compiler-rt/test/profile/Darwin/instrprof-debug-info-correlate.c b/compiler-rt/test/profile/Darwin/instrprof-debug-info-correlate.c
--- a/compiler-rt/test/profile/Darwin/instrprof-debug-info-correlate.c
+++ b/compiler-rt/test/profile/Darwin/instrprof-debug-info-correlate.c
@@ -18,3 +18,23 @@
 // RUN: llvm-profdata merge -o %t.cov.normal.profdata %t.cov.profraw
 
 // RUN: diff <(llvm-profdata show --all-functions --counts %t.cov.normal.profdata) <(llvm-profdata show --all-functions --counts %t.cov.profdata)
+
+// Test debug info correlate with online merging.
+
+// RUN: env LLVM_PROFILE_FILE=%t-1.profraw %run %t.normal
+// RUN: env LLVM_PROFILE_FILE=%t-2.profraw %run %t.normal
+// RUN: llvm-profdata merge -o %t.normal.profdata %t-1.profraw %t-2.profraw
+
+// RUN: rm -rf %t.profdir && mkdir %t.profdir
+// RUN: env LLVM_PROFILE_FILE=%t.profdir/%m.proflite %run %t
+// RUN: env LLVM_PROFILE_FILE=%t.profdir/%m.proflite %run %t
+// RUN: llvm-profdata merge -o %t.profdata --debug-info=%t.dSYM %t.profdir/
+
+// RUN: diff <(llvm-profdata show --all-functions --counts %t.normal.profdata) <(llvm-profdata show --all-functions --counts %t.profdata)
+
+// RUN: rm -rf %t.profdir && mkdir %t.profdir
+// RUN: env LLVM_PROFILE_FILE=%t.profdir/%m.cov.proflite %run %t.cov
+// RUN: env LLVM_PROFILE_FILE=%t.profdir/%m.cov.proflite %run %t.cov
+// RUN: llvm-profdata merge -o %t.cov.profdata --debug-info=%t.cov.dSYM %t.profdir/
+
+// RUN: diff <(llvm-profdata show --all-functions --counts %t.cov.normal.profdata) <(llvm-profdata show --all-functions --counts %t.cov.profdata)
diff --git a/compiler-rt/test/profile/Linux/instrprof-debug-info-correlate.c b/compiler-rt/test/profile/Linux/instrprof-debug-info-correlate.c
--- a/compiler-rt/test/profile/Linux/instrprof-debug-info-correlate.c
+++ b/compiler-rt/test/profile/Linux/instrprof-debug-info-correlate.c
@@ -24,3 +24,23 @@
 // RUN: llvm-profdata merge -o %t.cov.normal.profdata %t.cov.profraw
 
 // RUN: diff <(llvm-profdata show --all-functions --counts %t.cov.normal.profdata) <(llvm-profdata show --all-functions --counts %t.cov.profdata)
+
+// Test debug info correlate with online merging.
+
+// RUN: env LLVM_PROFILE_FILE=%t-1.profraw %run %t.normal
+// RUN: env LLVM_PROFILE_FILE=%t-2.profraw %run %t.normal
+// RUN: llvm-profdata merge -o %t.normal.profdata %t-1.profraw %t-2.profraw
+
+// RUN: rm -rf %t.profdir && mkdir %t.profdir
+// RUN: env LLVM_PROFILE_FILE=%t.profdir/%m.proflite %run %t
+// RUN: env LLVM_PROFILE_FILE=%t.profdir/%m.proflite %run %t
+// RUN: llvm-profdata merge -o %t.profdata --debug-info=%t %t.profdir/
+
+// RUN: diff <(llvm-profdata show --all-functions --counts %t.normal.profdata) <(llvm-profdata show --all-functions --counts %t.profdata)
+
+// RUN: rm -rf %t.profdir && mkdir %t.profdir
+// RUN: env LLVM_PROFILE_FILE=%t.profdir/%m.cov.proflite %run %t.cov
+// RUN: env LLVM_PROFILE_FILE=%t.profdir/%m.cov.proflite %run %t.cov
+// RUN: llvm-profdata merge -o %t.cov.profdata --debug-info=%t.cov %t.profdir/
+
+// RUN: diff <(llvm-profdata show --all-functions --counts %t.cov.normal.profdata) <(llvm-profdata show --all-functions --counts %t.cov.profdata)
diff --git a/compiler-rt/test/profile/instrprof-merge-empty-data.test b/compiler-rt/test/profile/instrprof-merge-empty-data.test
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/profile/instrprof-merge-empty-data.test
@@ -0,0 +1,14 @@
+// Test online merging with empty data section.
+// RUN: rm -rf %t.dir && split-file %s %t.dir && cd %t.dir
+// RUN: %clangxx_profgen -fcoverage-mapping -o %t main.c -fprofile-list=funlist
+// RUN: LLVM_PROFILE_FILE='a%m.profraw' %t
+// RUN: LLVM_PROFILE_FILE='a%m.profraw' %t 2>&1 | FileCheck %s --allow-empty
+
+// CHECK-NOT: LLVM Profile Error
+
+//--- main.c
+int main() {}
+
+//--- funlist
+[clang]
+default:skip
diff --git a/compiler-rt/test/profile/instrprof-merge-error.c b/compiler-rt/test/profile/instrprof-merge-error.c
--- a/compiler-rt/test/profile/instrprof-merge-error.c
+++ b/compiler-rt/test/profile/instrprof-merge-error.c
@@ -1,11 +1,5 @@
 // RUN: rm -rf %t; mkdir %t
 
-// RUN: %clang_pgogen -o %t/dbg -g -mllvm --debug-info-correlate -mllvm --disable-vp=true %s
-// RUN: env LLVM_PROFILE_FILE=%t/dbg_%m.profdata %run %t/dbg 2>&1 | count 0
-// RUN: env LLVM_PROFILE_FILE=%t/dbg_%m.profdata %run %t/dbg 2>&1 | FileCheck %s --check-prefix=DBG
-
-// DBG: Debug info correlation does not support profile merging at runtime.
-
 // RUN: %clang_pgogen -o %t/timeprof -mllvm -pgo-temporal-instrumentation %s
 // RUN: env LLVM_PROFILE_FILE=%t/timeprof_%m.profdata %run %t/timeprof 2>&1 | count 0
 // RUN: env LLVM_PROFILE_FILE=%t/timeprof_%m.profdata %run %t/timeprof 2>&1 | FileCheck %s --check-prefix=TIMEPROF