[PATCH] D10980: [lld] COFF: Fix bug involving archives defining a symbol multiple times.

[Peter Collingbourne]

pcc added a reviewer: ruiu.
pcc added a subscriber: llvm-commits.

Previously we were unnecessarily loading lazy symbols if they appeared in an
archive multiple times, as can happen with comdat symbols. This change fixes
the bug by only loading symbols from archives at load time if the original
symbol was undefined.

http://reviews.llvm.org/D10980

Files:
  COFF/SymbolTable.cpp
  test/COFF/ar-comdat.test

Index: test/COFF/ar-comdat.test
===================================================================
--- /dev/null
+++ test/COFF/ar-comdat.test
@@ -0,0 +1,38 @@
+# RUN: yaml2obj %s > %t1.obj
+# RUN: yaml2obj %s > %t2.obj
+# RUN: llvm-lib /out:%t.lib %t1.obj %t2.obj
+# RUN: lld -flavor link2 /out:%t.exe /lldmap:%t.map /entry:main /subsystem:console %p/Inputs/ret42.obj %t.lib
+# RUN: FileCheck %s < %t.map
+
+# CHECK-NOT: .lib
+
+---
+header:          
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:        
+  - Name:            .bss
+    Characteristics: [ IMAGE_SCN_CNT_UNINITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     ''
+symbols:         
+  - Name:            .bss
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition: 
+      Length:          4
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          1
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  - Name:            x
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...
Index: COFF/SymbolTable.cpp
===================================================================
--- COFF/SymbolTable.cpp
+++ COFF/SymbolTable.cpp
@@ -177,7 +177,8 @@
     if (!Sym->Body.compare_exchange_strong(Existing, New))
       continue;
     New->setBackref(Sym);
-    Accum->push_back(Sym);
+    if (isa<Undefined>(Existing))
+      Accum->push_back(Sym);
     return;
   }
 }


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