COFF: Allow ICFing sections with different alignments.

[pcc]

Summary

The combined section gets the maximum alignment of all sections.

[hans]

Looks good to me.

COFF/Chunks.cpp

 
 ArrayRef<uint8_t> SectionChunk::getContents() const {
   ArrayRef<uint8_t> A;
   File->getCOFFObj()->getSectionContents(Header, A);
   return A;
 }
 
 void SectionChunk::replace(SectionChunk *Other) {
+  Alignment = std::max(Alignment, Other->Alignment);
   Other->Repl = Repl;
   Other->Live = false;
 }
 
 CommonChunk::CommonChunk(const COFFSymbolRef S) : Sym(S) {
   // Common symbols are aligned on natural boundaries up to 32 bytes.
   // This is what MSVC link.exe does.
   Alignment = std::min(uint64_t(32), PowerOf2Ceil(Sym.getValue()));

COFF/ICF.cpp

private:
 
   std::vector<SectionChunk *> Chunks;
   int Cnt = 0;
   std::atomic<bool> Repeat = {false};
 };
 
 // Returns a hash value for S.
 uint32_t ICF::getHash(SectionChunk *C) {
-  return hash_combine(C->getOutputCharacteristics(), C->SectionName, C->Relocs.size(),
-                      C->Alignment, uint32_t(C->Header->SizeOfRawData),
+  return hash_combine(C->getOutputCharacteristics(), C->SectionName,
+                      C->Relocs.size(), uint32_t(C->Header->SizeOfRawData),
                       C->Checksum, C->getContents());
 }
 
 // Returns true if section S is subject of ICF.
 //
 // Microsoft's documentation
 // (https://msdn.microsoft.com/en-us/library/bxwfs976.aspx; visited April
 // 2017) says that /opt:icf folds both functions and read-only data.
if (auto *D1 = dyn_cast<DefinedRegular>(B1))
                D1->getChunk()->Class[Cnt % 2] == D2->getChunk()->Class[Cnt % 2];
     return false;
   };
   if (!std::equal(A->Relocs.begin(), A->Relocs.end(), B->Relocs.begin(), Eq))
     return false;
 
   // Compare section attributes and contents.
   return A->getOutputCharacteristics() == B->getOutputCharacteristics() &&
-         A->SectionName == B->SectionName && A->Alignment == B->Alignment &&
+         A->SectionName == B->SectionName &&
          A->Header->SizeOfRawData == B->Header->SizeOfRawData &&
          A->Checksum == B->Checksum && A->getContents() == B->getContents() &&
          assocEquals(A, B);
 }
 
 // Compare "moving" part of two sections, namely relocation targets.
 bool ICF::equalsVariable(const SectionChunk *A, const SectionChunk *B) {
   // Compare relocations.

test/COFF/icf-different-align.test

 # RUN: yaml2obj < %s > %t.obj
 # RUN: lld-link /entry:foo /out:%t.exe /subsystem:console /include:bar \
 # RUN:   /verbose %t.obj > %t.log 2>&1
 # RUN: FileCheck %s < %t.log
+# RUN: llvm-objdump -s %t.exe | FileCheck --check-prefix=OBJDUMP %s
 
-# CHECK-NOT: Selected foo
-# CHECK-NOT:   Removed bar
+# CHECK: Selected foo
+# CHECK:   Removed bar
+
+# OBJDUMP: Contents of section .text:
+# OBJDUMP-NEXT: 140001000 00cccccc cccccccc cccccccc cccccccc
+# OBJDUMP-NEXT: 140001010 4883ec28 e8000000 004883c4 28c3
 
 --- !COFF
 header:
   Machine:         IMAGE_FILE_MACHINE_AMD64
   Characteristics: []
 sections:
   - Name:            '.text$mn'
     Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
     Alignment:       8
     SectionData:     4883EC28E8000000004883C428C3
   - Name:            '.text$mn'
     Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
     Alignment:       16
     SectionData:     4883EC28E8000000004883C428C3
+  - Name:            '.text'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       1
+    SectionData:     00
 symbols:
   - Name:            '.text$mn'
     Value:           0
     SectionNumber:   1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_STATIC
     SectionDefinition: