[lld] r288483 - Fix a bug in ICF involving COFF associative sections.

[Rui Ueyama via llvm-commits]

Author: ruiu
Date: Fri Dec  2 01:46:12 2016
New Revision: 288483

URL: http://llvm.org/viewvc/llvm-project?rev=288483&view=rev
Log:
Fix a bug in ICF involving COFF associative sections.

Associative sections are sections that need to be linked if their associated
sections are linked. Associative sections are used to append auxiliary data
such as debug info.

Previously, we compared all associative sections when comparing two comdat
sections. Because usually assocative sections are not mergeable sections,
we missed a lot of mergeable sections. MSVC linker doesn't seem to check
the identity of associative sections.

This patch makes LLD to ignore associative sections when doing ICF.

Added:
    lld/trunk/test/COFF/icf-associative.test
Modified:
    lld/trunk/COFF/ICF.cpp

Modified: lld/trunk/COFF/ICF.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/ICF.cpp?rev=288483&r1=288482&r2=288483&view=diff
==============================================================================
--- lld/trunk/COFF/ICF.cpp (original)
+++ lld/trunk/COFF/ICF.cpp Fri Dec  2 01:46:12 2016
@@ -95,11 +95,6 @@ bool ICF::equalsConstant(const SectionCh
     return false;
   }
 
-  // Compare associative sections.
-  for (size_t I = 0, E = A->AssocChildren.size(); I != E; ++I)
-    if (A->AssocChildren[I]->GroupID != B->AssocChildren[I]->GroupID)
-      return false;
-
   // Compare relocations.
   auto Eq = [&](const coff_relocation &R1, const coff_relocation &R2) {
     if (R1.Type != R2.Type ||
@@ -129,11 +124,6 @@ bool ICF::equalsConstant(const SectionCh
 }
 
 bool ICF::equalsVariable(const SectionChunk *A, const SectionChunk *B) {
-  // Compare associative sections.
-  for (size_t I = 0, E = A->AssocChildren.size(); I != E; ++I)
-    if (A->AssocChildren[I]->GroupID != B->AssocChildren[I]->GroupID)
-      return false;
-
   // Compare relocations.
   auto Eq = [&](const coff_relocation &R1, const coff_relocation &R2) {
     SymbolBody *B1 = A->File->getSymbolBody(R1.SymbolTableIndex)->repl();

Added: lld/trunk/test/COFF/icf-associative.test
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/COFF/icf-associative.test?rev=288483&view=auto
==============================================================================
--- lld/trunk/test/COFF/icf-associative.test (added)
+++ lld/trunk/test/COFF/icf-associative.test Fri Dec  2 01:46:12 2016
@@ -0,0 +1,104 @@
+# RUN: yaml2obj < %s > %t.obj
+# RUN: lld-link /entry:foo /out:%t.exe /subsystem:console /include:bar \
+# RUN:   /debug /verbose %t.obj > %t.log 2>&1
+# RUN: FileCheck %s < %t.log
+
+# CHECK: Selected foo
+# CHECK:   Removed bar
+
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: []
+sections:
+  - Name:            '.text$mn'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     4883EC28E8000000004883C428C3
+
+  - Name:            '.debug$S'
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
+    Alignment:       1
+    SectionData:     0000000000000000000000000000
+
+  - Name:            '.text$mn'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     4883EC28E8000000004883C428C3
+
+  - Name:            '.debug$S'
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
+    Alignment:       1
+    SectionData:     FFFFFFFFFFFFFFFFFFFFFFFFFFFF
+
+symbols:
+  - Name:            '.text$mn'
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          14
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        1682752513
+      Number:          0
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+
+  - Name:            '.debug$S'
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          14
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          1
+      Selection:       IMAGE_COMDAT_SELECT_ASSOCIATIVE
+
+  - Name:            '.text$mn'
+    Value:           0
+    SectionNumber:   3
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          14
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        1682752513
+      Number:          0
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+
+  - Name:            '.debug$S'
+    Value:           0
+    SectionNumber:   4
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          14
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          3
+      Selection:       IMAGE_COMDAT_SELECT_ASSOCIATIVE
+
+  - Name:            foo
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+
+  - Name:            bar
+    Value:           0
+    SectionNumber:   3
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...