COFF: Merge .bss into .data by default.

[pcc]

Summary

Depends on D45801

[ruiu]

LGTM

lld/COFF/Driver.cpp

void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   for (auto *Arg : Args.filtered(OPT_merge))
     parseMerge(Arg->getValue());
 
   // Add default section merging rules after user rules. User rules take
   // precedence, but we will emit a warning if there is a conflict.
   parseMerge(".idata=.rdata");
   parseMerge(".didat=.rdata");
   parseMerge(".edata=.rdata");
+  parseMerge(".bss=.data");
 
   // Handle /section
   for (auto *Arg : Args.filtered(OPT_section))
     parseSection(Arg->getValue());
 
   // Handle /aligncomm
   for (auto *Arg : Args.filtered(OPT_aligncomm))
     parseAligncomm(Arg->getValue());

lld/test/COFF/common-alignment.test

- Name:            .text
     SectionData:     b800000000b800000000
     Relocations:
       - VirtualAddress:  1
         SymbolName:      bssdata4
         Type:            IMAGE_REL_AMD64_ADDR32
       - VirtualAddress:  6
         SymbolName:      bssdata4_align16
         Type:            IMAGE_REL_AMD64_ADDR32
-  - Name:            .data
-    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
-    Alignment:       4
-    SectionData:     03000000
   - Name:            .drectve
     Characteristics: [ IMAGE_SCN_LNK_INFO, IMAGE_SCN_LNK_REMOVE ]
     Alignment:       1
     SectionData:     202d616c69676e636f6d6d3a62737364617461345f616c69676e31362c340a  # -aligncomm:bssdata4_align16,4
 
 symbols:
   - Name:            .text
     Value:           0
     SectionNumber:   1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_STATIC
     SectionDefinition:
       Length:          0
       NumberOfRelocations: 5
       NumberOfLinenumbers: 0
       CheckSum:        0
       Number:          0
-  - Name:            .data
-    Value:           0
-    SectionNumber:   2
-    SimpleType:      IMAGE_SYM_TYPE_NULL
-    ComplexType:     IMAGE_SYM_DTYPE_NULL
-    StorageClass:    IMAGE_SYM_CLASS_STATIC
-    SectionDefinition:
-      Length:          4
-      NumberOfRelocations: 0
-      NumberOfLinenumbers: 0
-      CheckSum:        0
-      Number:          0
   - Name:            main
     Value:           0
     SectionNumber:   1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
     StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
   - Name:            bssdata4
     Value:           4

lld/test/COFF/common.test

Relocations:
         SymbolName:      bssdata64
         Type:            IMAGE_REL_AMD64_ADDR32
       - VirtualAddress:  16
         SymbolName:      bsspad2
         Type:            IMAGE_REL_AMD64_ADDR32
       - VirtualAddress:  21
         SymbolName:      bssdata16
         Type:            IMAGE_REL_AMD64_ADDR32
-  - Name:            .data
-    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
-    Alignment:       4
-    SectionData:     03000000
 symbols:
   - Name:            .text
     Value:           0
     SectionNumber:   1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_STATIC
     SectionDefinition:
       Length:          0
       NumberOfRelocations: 5
       NumberOfLinenumbers: 0
       CheckSum:        0
       Number:          0
-  - Name:            .data
-    Value:           0
-    SectionNumber:   2
-    SimpleType:      IMAGE_SYM_TYPE_NULL
-    ComplexType:     IMAGE_SYM_DTYPE_NULL
-    StorageClass:    IMAGE_SYM_CLASS_STATIC
-    SectionDefinition:
-      Length:          4
-      NumberOfRelocations: 0
-      NumberOfLinenumbers: 0
-      CheckSum:        0
-      Number:          0
   - Name:            main
     Value:           0
     SectionNumber:   1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
     StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
   - Name:            bssdata4
     Value:           4

lld/test/COFF/pdb-globals.test

 CHECK-NEXT:            module = 1, sum name = 0, offset = 52
 CHECK-NEXT:      188 | S_PROCREF [size = 20] `main`
 CHECK-NEXT:            module = 1, sum name = 0, offset = 108
 CHECK-NEXT:      208 | S_LPROCREF [size = 24] `LocalFunc`
 CHECK-NEXT:            module = 1, sum name = 0, offset = 292
 CHECK-NEXT:      312 | S_PROCREF [size = 40] `HelloPoint::HelloPoint`
 CHECK-NEXT:            module = 1, sum name = 0, offset = 376
 CHECK-NEXT:      232 | S_GDATA32 [size = 28] `__purecall`
-CHECK-NEXT:            type = 0x0403 (void*), addr = 0000:0000
+CHECK-NEXT:            type = 0x0403 (void*), addr = 0003:0004
 CHECK-NEXT:      260 | S_GDATA32 [size = 24] `GlobalVar`
 CHECK-NEXT:            type = 0x100B (const int*), addr = 0003:0000
 CHECK-NEXT:      284 | S_LDATA32 [size = 28] `ConstantVar`
 CHECK-NEXT:            type = 0x100A (const int), addr = 0002:0000
 
 CHECK-LABEL:                           Symbols
 CHECK-NEXT:  ============================================================
 CHECK-NEXT:    Mod 0000
 CHECK-NOT:              | S_GDATA32
 CHECK-NOT:              | S_UDT
 CHECK:               52 | S_GPROC32 [size = 52] `GlobalFunc`
 CHECK:              108 | S_GPROC32 [size = 44] `main`
 CHECK:              292 | S_LPROC32 [size = 52] `LocalFunc`
 CHECK:              348 | S_LDATA32 [size = 28] `ConstantVar`
 CHECK:              376 | S_GPROC32 [size = 64] `HelloPoint::HelloPoint`

lld/test/COFF/secrel-common.s

 # RUN: llvm-mc %s -filetype=obj -triple=x86_64-windows-msvc -o %t.obj
 # RUN: lld-link -entry:main -nodefaultlib %t.obj -out:%t.exe
 # RUN: llvm-readobj %t.exe -sections -section-data | FileCheck %s
 
-# Section relocations against common symbols resolve to .bss.
+# Section relocations against common symbols resolve to .bss (merged into .data).
 
 # CHECK: Sections [
 # CHECK:   Section {
 # CHECK:     Number: 1
 # CHECK:     Name: .text (2E 74 65 78 74 00 00 00)
 # CHECK:     VirtualSize: 0x1
 # CHECK:     SectionData (
 # CHECK:       0000: C3                                   |.|
 # CHECK:     )
 # CHECK:   }
 # CHECK:   Section {
 # CHECK:     Number: 2
-# CHECK:     Name: .bss (2E 62 73 73 00 00 00 00)
-# CHECK:     VirtualSize: 0x4
-# CHECK:   }
-# CHECK:   Section {
-# CHECK:     Number: 3
 # CHECK:     Name: .rdata (2E 72 64 61 74 61 00 00)
 # CHECK:     SectionData (
-# CHECK:       0000: 00000000 02000000 |........|
+# CHECK:       0000: 00020000 03000000 |........|
 # CHECK:     )
 # CHECK:   }
+# CHECK:   Section {
+# CHECK:     Number: 3
+# CHECK:     Name: .data (2E 64 61 74 61 00 00 00)
+# CHECK:     VirtualSize: 0x204
+# CHECK:     RawDataSize: 512
+# CHECK:   }
 # CHECK-NOT: Section
 # CHECK: ]
 
 .text
 .global main
 main:
 ret
 
 .comm   common_global,4,2
 
 .section .rdata,"dr"
 .secrel32 common_global
 .secidx common_global
 .short 0
+
+.section .data,"drw"
+.zero 512

lld/test/COFF/section-size.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-windows-msvc %s -o %tmain.obj
 # RUN: echo '.lcomm s, 0x80000000' | llvm-mc -filetype=obj -triple=x86_64-windows-msvc -o %t1.obj
 # RUN: cp %t1.obj %t2.obj
 # RUN: echo '.lcomm s, 0xffffffff' | llvm-mc -filetype=obj -triple=x86_64-windows-msvc -o %t3.obj
 
 # Run: lld-link -entry:main %tmain.obj %t3.obj -out:%t.exe
 
 # RUN: not lld-link -entry:main %tmain.obj %t1.obj %t2.obj -out:%t.exe 2>&1 | FileCheck %s
-# CHECK: error: section larger than 4 GiB: .bss
+# CHECK: error: section larger than 4 GiB: .data
 
 .globl main
 main:
   retq