COFF: Fix ICF correctness bug.

When comparing two COMDAT sections, we need to take section values
and associative sections into account. This patch fixes that bug.
It fixes a crash bug of llvm-tblgen when linked with /opt:lldicf.

One thing I don't understand yet is that this logic seems to be
too strict. MSVC linker is able to create more compact executables
(which of course work correctly). With this ICF algorithm, LLD is
able to make executable smaller, but the outputs are larger than
MSVC's. There must be something I'm missing here.

llvm-svn: 240897

lld/COFF/Chunks.cpp

@@ -173,6 +173,13 @@ bool SectionChunk::equals(const SectionChunk *X) const {
   if (getContents() != X->getContents())
     return false;
 
+  // Compare associative sections
+  if (AssocChildren.size() != X->AssocChildren.size())
+    return false;
+  for (size_t I = 0, E = AssocChildren.size(); I != E; ++I)
+    if (AssocChildren[I]->Ptr != X->AssocChildren[I]->Ptr)
+      return false;
+
   // Compare relocations
   auto Eq = [&](const coff_relocation &R1, const coff_relocation &R2) {
     if (R1.Type != R2.Type)
@@ -181,11 +188,13 @@ bool SectionChunk::equals(const SectionChunk *X) const {
       return false;
     SymbolBody *B1 = File->getSymbolBody(R1.SymbolTableIndex);
     SymbolBody *B2 = X->File->getSymbolBody(R2.SymbolTableIndex);
+    if (B1 == B2)
+      return true;
     auto *D1 = dyn_cast<DefinedRegular>(B1);
     auto *D2 = dyn_cast<DefinedRegular>(B2);
-    if (D1 && D2 && D1->getChunk() == D2->getChunk())
-      return true;
-    return B1 == B2;
+    return (D1 && D2 &&
+            D1->getValue() == D2->getValue() &&
+            D1->getChunk() == D2->getChunk());
   };
   return std::equal(Relocs.begin(), Relocs.end(), X->Relocs.begin(), Eq);
 }

lld/COFF/Chunks.h

@@ -151,7 +151,7 @@ private:
 
   const coff_section *Header;
   StringRef SectionName;
-  std::vector<Chunk *> AssocChildren;
+  std::vector<SectionChunk *> AssocChildren;
   llvm::iterator_range<const coff_relocation *> Relocs;
   size_t NumRelocs;
 

lld/COFF/Symbols.h

@@ -137,6 +137,7 @@ public:
   bool isLive() const { return (*Data)->isLive(); }
   void markLive() { (*Data)->markLive(); }
   Chunk *getChunk() { return *Data; }
+  uint64_t getValue() { return Sym.getValue(); }
 
 private:
   StringRef Name;

lld/test/COFF/Inputs/icf4.yaml

@@ -0,0 +1,47 @@
+---
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: []
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     0000000000000000
+  - Name:            .assoc
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     0000000000000000
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          8
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  # icf4 is *not* identical with mainCRTStartup because it has an associative section
+  - Name:            icf4
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            .assoc
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          8
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          1
+      Selection:       IMAGE_COMDAT_SELECT_ASSOCIATIVE

lld/test/COFF/Inputs/icf5.yaml

@@ -0,0 +1,30 @@
+---
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: []
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     0000000000000000
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          8
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  # icf5 is *not* identical with its symbol value is different
+  - Name:            icf5
+    Value:           5
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL

lld/test/COFF/icf.test

@@ -1,11 +1,16 @@
 # RUN: yaml2obj < %p/Inputs/icf1.yaml > %t1.obj
 # RUN: yaml2obj < %p/Inputs/icf2.yaml > %t2.obj
 # RUN: yaml2obj < %p/Inputs/icf3.yaml > %t3.obj
+# RUN: yaml2obj < %p/Inputs/icf4.yaml > %t4.obj
+# RUN: yaml2obj < %p/Inputs/icf5.yaml > %t5.obj
 #
-# RUN: lld -flavor link2 /out:%t.exe %t1.obj %t2.obj %t3.obj \
-# RUN:   /opt:lldicf /include:icf2 /include:icf3 /verbose >& %t.log
+# RUN: lld -flavor link2 /out:%t.exe %t1.obj %t2.obj %t3.obj %t4.obj %t5.obj \
+# RUN:   /opt:lldicf /include:icf2 /include:icf3 /include:icf4 /include:icf5 \
+# RUN:   /verbose >& %t.log
 # RUN: FileCheck %s < %t.log
 
 CHECK-NOT: Replaced mainCRTStartup
 CHECK:     Replaced icf2
 CHECK-NOT: Replaced icf3
+CHECK-NOT: Replaced icf4
+CHECK-NOT: Replaced icf5