[BOLT] Always treat function entry as code (#160161)

If an address has both, a data marker "$d" and a function symbol
associated with it, treat it as code.

Author: maksfb

bolt/lib/Rewrite/RewriteInstance.cpp

@@ -917,9 +917,6 @@ void RewriteInstance::discoverFileObjects() {
     bool IsData = false;
     uint64_t LastAddr = 0;
     for (const auto &SymInfo : SortedSymbols) {
-      if (LastAddr == SymInfo.Address) // don't repeat markers
-        continue;
-
       MarkerSymType MarkerType = BC->getMarkerType(SymInfo.Symbol);
 
       // Treat ST_Function as code.
@@ -929,8 +926,14 @@ void RewriteInstance::discoverFileObjects() {
         if (IsData) {
           Expected<StringRef> NameOrError = SymInfo.Symbol.getName();
           consumeError(NameOrError.takeError());
-          BC->errs() << "BOLT-WARNING: function symbol " << *NameOrError
-                     << " lacks code marker\n";
+          if (LastAddr == SymInfo.Address) {
+            BC->errs() << "BOLT-WARNING: ignoring data marker conflicting with "
+                          "function symbol "
+                       << *NameOrError << '\n';
+          } else {
+            BC->errs() << "BOLT-WARNING: function symbol " << *NameOrError
+                       << " lacks code marker\n";
+          }
         }
         MarkerType = MarkerSymType::CODE;
       }

bolt/test/AArch64/data-at-0-offset.c

@@ -0,0 +1,23 @@
+## Check that if a data marker is present at the start of a function, the
+## underlying bytes are still treated as code.
+
+# RUN: %clang %cflags %s -o %t.exe
+# RUN: llvm-bolt %t.exe -o %t.bolt --print-cfg 2>&1 | FileCheck %s
+
+# CHECK: BOLT-WARNING: ignoring data marker conflicting with function symbol _start
+
+.text
+.balign 4
+
+## Data marker is emitted because ".long" directive is used instead of ".inst".
+.global _start
+.type _start, %function
+_start:
+  .long 0xcec08000 // sha512su0 v0.2d, v0.2d
+  ret
+.size _start, .-_start
+
+# CHECK-LABEL: Binary Function "_start"
+# CHECK: Entry Point
+# CHECK-NEXT: sha512su0 v0.2d, v0.2d
+