Always emit symbol table when dwarf section exists in COFF

This also fixes check prefix NO which is pointless in symtab.test

Reviewed By: mstorsjo

Differential Revision: https://reviews.llvm.org/D149235

lld/COFF/Writer.cpp

@@ -1266,7 +1266,9 @@ void Writer::createSymbolAndStringTable() {
   // solution where discardable sections have long names preserved and
   // non-discardable sections have their names truncated, to ensure that any
   // section which is mapped at runtime also has its name mapped at runtime.
+  bool HasDwarfSection = false;
   for (OutputSection *sec : ctx.outputSections) {
+    HasDwarfSection |= sec->name.startswith(".debug_");
     if (sec->name.size() <= COFF::NameSize)
       continue;
     if ((sec->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE) == 0)
@@ -1279,7 +1281,7 @@ void Writer::createSymbolAndStringTable() {
     sec->setStringTableOff(addEntryToStringTable(sec->name));
   }
 
-  if (ctx.config.debugDwarf || ctx.config.debugSymtab) {
+  if (ctx.config.debugDwarf || ctx.config.debugSymtab || HasDwarfSection) {
     for (ObjFile *file : ctx.objFileInstances) {
       for (Symbol *b : file->getSymbols()) {
         auto *d = dyn_cast_or_null<Defined>(b);

lld/test/COFF/symtab.test

@@ -8,6 +8,8 @@
 
 # RUN: lld-link /debug /out:%t.exe /entry:main %t.obj %p/Inputs/std64.lib
 # RUN: llvm-readobj --symbols %t.exe | FileCheck -check-prefix=NO %s
+# RUN: lld-link /debug /merge:.blank=.debug_info /out:%t.exe /entry:main %t.obj %p/Inputs/std64.lib
+# RUN: llvm-readobj --symbols %t.exe | FileCheck %s
 
 # CHECK:      Symbols [
 # CHECK-NEXT:   Symbol {
@@ -84,7 +86,8 @@
 # CHECK-NEXT:   }
 # CHECK-NEXT: ]
 
-# NO: Symbols [
+# NO:       Symbols [
+# NO-NEXT:  ]
 
 --- !COFF
 header:
@@ -141,6 +144,10 @@ sections:
     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
     Alignment:       4
     SectionData:     48656C6C6F0048656C6C6F20576F726C6400
+  - Name:            .blank
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
+    Alignment:       1
+    SectionData:     0000
 symbols:
   - Name:            "@comp.id"
     Value:           10394907