[lld] r254578 - COFF: Non-external COMDAT sections sholud not be merged by ICF.

[Rui Ueyama via llvm-commits]

Author: ruiu
Date: Wed Dec  2 20:23:33 2015
New Revision: 254578

URL: http://llvm.org/viewvc/llvm-project?rev=254578&view=rev
Log:
COFF: Non-external COMDAT sections sholud not be merged by ICF.

If a section symbol is not external, that COMDAT section should never
be merge with other sections in other compilation unit. Previously,
we didn't take visibility into account.

Note that COMDAT sections with non-external visibility makes sense
because they can be removed by dead-stripping.

Fixes https://llvm.org/bugs/show_bug.cgi?id=25686

Added:
    lld/trunk/test/COFF/icf-local.test
Modified:
    lld/trunk/COFF/Chunks.h
    lld/trunk/COFF/ICF.cpp

Modified: lld/trunk/COFF/Chunks.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Chunks.h?rev=254578&r1=254577&r2=254578&view=diff
==============================================================================
--- lld/trunk/COFF/Chunks.h (original)
+++ lld/trunk/COFF/Chunks.h Wed Dec  2 20:23:33 2015
@@ -204,8 +204,7 @@ private:
   void replace(SectionChunk *Other);
   std::atomic<uint64_t> GroupID = { 0 };
 
-  // Chunks are basically unnamed chunks of bytes.
-  // Symbols are associated for debugging and logging purposs only.
+  // Sym points to a section symbol if this is a COMDAT chunk.
   DefinedRegular *Sym = nullptr;
 };
 

Modified: lld/trunk/COFF/ICF.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/ICF.cpp?rev=254578&r1=254577&r2=254578&view=diff
==============================================================================
--- lld/trunk/COFF/ICF.cpp (original)
+++ lld/trunk/COFF/ICF.cpp Wed Dec  2 20:23:33 2015
@@ -185,8 +185,9 @@ void ICF::run(const std::vector<Chunk *>
   // Collect only mergeable sections and group by hash value.
   parallel_for_each(Vec.begin(), Vec.end(), [&](Chunk *C) {
     if (auto *SC = dyn_cast<SectionChunk>(C)) {
+      bool Global = SC->Sym && SC->Sym->isExternal();
       bool Writable = SC->getPermissions() & llvm::COFF::IMAGE_SCN_MEM_WRITE;
-      if (SC->isCOMDAT() && SC->isLive() && !Writable)
+      if (SC->isCOMDAT() && SC->isLive() && Global && !Writable)
         SC->GroupID = getHash(SC) | (uint64_t(1) << 63);
     }
   });

Added: lld/trunk/test/COFF/icf-local.test
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/COFF/icf-local.test?rev=254578&view=auto
==============================================================================
--- lld/trunk/test/COFF/icf-local.test (added)
+++ lld/trunk/test/COFF/icf-local.test Wed Dec  2 20:23:33 2015
@@ -0,0 +1,66 @@
+# COMDAT sections with non-external linkage should not be merged by ICF.
+
+# RUN: yaml2obj < %s > %t1.obj
+# RUN: sed s/foo/main/ %s | yaml2obj > %t2.obj
+# RUN: lld-link /out:%t.exe /entry:main /subsystem:console /verbose \
+# RUN:   %t1.obj %t2.obj > %t.log 2>&1
+# RUN: FileCheck %s < %t.log
+
+# CHECK-NOT: Removed bar
+
+---
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: []
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     488D0500000000C3
+    Relocations:
+      - VirtualAddress:  3
+        SymbolName:      bar
+        Type:            IMAGE_REL_AMD64_REL32
+  - Name:            .rdata
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_READ ]
+    Alignment:       8
+    SectionData:     2A000000000000002B00000000000000
+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: 1
+      NumberOfLinenumbers: 0
+      CheckSum:        1092178131
+      Number:          1
+  - Name:            .rdata
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          16
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        1200668497
+      Number:          5
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  - 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:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+...