[lld] COFF: When resolving _load_config_used, add it as a GC root.

[pcc]

Summary

This fixes the cases where the symbol is defined in a comdat or by bitcode.

[ruiu]

LGTM

COFF/Driver.cpp

for (auto Pair : Config->AlternateNames) {
       if (!Sym)
         continue;
       if (auto *U = dyn_cast<Undefined>(Sym->Body))
         if (!U->WeakAlias)
           U->WeakAlias = Symtab.addUndefined(To);
     }
 
     // Windows specific -- if __load_config_used can be resolved, resolve it.
-    if (Symbol *Sym = Symtab.find(Config->LoadConfigUsed))
-      if (isa<Lazy>(Sym->Body))
-        Symtab.addUndefined(Config->LoadConfigUsed);
+    if (Symtab.find(Config->LoadConfigUsed))
+      addUndefined(Config->LoadConfigUsed);
 
     if (Symtab.queueEmpty())
       break;
     if (auto EC = Symtab.run()) {
       llvm::errs() << EC.message() << "\n";
       return false;
     }
   }

test/COFF/loadcfg.ll

+; RUN: llvm-as -o %t.obj %s
+; RUN: lld -flavor link2 /out:%t.exe %t.obj /entry:main /subsystem:console
+; RUN: llvm-readobj -file-headers %t.exe | FileCheck %s
+
+; CHECK: LoadConfigTableRVA: 0x1000
+; CHECK: LoadConfigTableSize: 0x70
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+@_load_config_used = constant i32 1
+
+define void @main() {
+  ret void
+}

test/COFF/loadcfg.test

 # RUN: yaml2obj < %s > %t.obj
 # RUN: lld -flavor link2 /out:%t.exe %t.obj /entry:main /subsystem:console
 # RUN: llvm-readobj -file-headers %t.exe | FileCheck %s
 
-# CHECK: LoadConfigTableRVA: 0x1000
+# CHECK: LoadConfigTableRVA: 0x1008
 # CHECK: LoadConfigTableSize: 0x70
 
 ---
 header:
   Machine:         IMAGE_FILE_MACHINE_AMD64
   Characteristics: []
 sections:
   - Name:            .text
     Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
     Alignment:       4
     SectionData:     B82A000000C3
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       4
+    SectionData:     B82A000000C3
 symbols:
   - Name:            .text
     Value:           0
     SectionNumber:   1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_STATIC
     SectionDefinition:
       Length:          6
       NumberOfRelocations: 0
       NumberOfLinenumbers: 0
       CheckSum:        0
       Number:          0
+  - Name:            .text
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          6
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+      Selection:       IMAGE_COMDAT_SELECT_ANY
   - Name:            main
     Value:           0
     SectionNumber:   1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
   - Name:            _load_config_used
     Value:           0
-    SectionNumber:   1
+    SectionNumber:   2
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
 ...