[JITLink][COFF] Implement IMAGE_SYM_CLASS_LABEL.

[sunho]

Summary

Implements IMAGE_SYM_CLASS_LABEL. It's simply a section + offset. This is not used a lot by llvm mc but very commonly used by MSVC compiler.

[sgraenitz]

LGTM

llvm/lib/ExecutionEngine/JITLink/COFFLinkGraphBuilder.cpp

if (!isComdatSection(Section)) {
       if (!PendingComdatExports[Symbol.getSectionNumber()])
         return make_error<JITLinkError>("No pending COMDAT export for symbol " +
                                         formatv("{0:d}", SymIndex));
 
       return exportCOMDATSymbol(SymIndex, SymbolName, Symbol);
     }
   }
 
-  if (Symbol.getStorageClass() == COFF::IMAGE_SYM_CLASS_STATIC) {
+  if (Symbol.getStorageClass() == COFF::IMAGE_SYM_CLASS_STATIC ||
+      Symbol.getStorageClass() == COFF::IMAGE_SYM_CLASS_LABEL) {
     const object::coff_aux_section_definition *Definition =
         Symbol.getSectionDefinition();
     if (!Definition || !isComdatSection(Section)) {
       // Handle typical static symbol
       return &G->addDefinedSymbol(
           *B, Symbol.getValue(), SymbolName, 0, Linkage::Strong, Scope::Local,
           Symbol.getComplexType() == COFF::IMAGE_SYM_DTYPE_FUNCTION, false);
     }

llvm/test/ExecutionEngine/JITLink/X86/COFF_label.test

+# RUN: yaml2obj %s -o %t
+# RUN: llvm-jitlink -noexec \
+# RUN: -slab-allocate 100Kb -slab-address 0xfff00000 -slab-page-size 4096 \
+# RUN: -show-graph -noexec %t 2>&1 | FileCheck %s
+#
+# Check a label symbol with an offset is created as defined symbol.
+#
+# CHECK:   block 0xfff00000 size = 0x00000028, align = 16, alignment-offset = 0
+# CHECK-NEXT: symbols:
+# CHECK-NEXT:   0xfff00000 (block + 0x00000000): size: 0x00000013, linkage: strong, scope: default, live  -   main
+# CHECK-NEXT:   0xfff00013 (block + 0x00000013): size: 0x00000015, linkage: strong, scope: local, live  -   $LN4
+
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:
+  - Name:            '.text$mn'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     4883EC28488D542438E8000000004883C428C34883EC28488D54243033C9E8000000004883C428C3
+  - Name:            '.sect'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     4883EC28488D542438E8000000004883C428C34883EC28488D54243033C9E8000000004883C428C3
+    Relocations:
+      - VirtualAddress:  10
+        SymbolTableIndex: 2
+        Type:            IMAGE_REL_AMD64_REL32
+symbols:
+  - Name:            '.text$mn'
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          53
+      NumberOfRelocations: 1
+      NumberOfLinenumbers: 0
+      CheckSum:        973622814
+      Number:          0
+  - Name:            '$LN4'
+    Value:           19
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_LABEL
+  - Name:            main
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            func
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...