[WebAssembly] Don't export __data_end and __heap_start by default.

[sbc100]

Summary

These can still be exported via --export if needed.

This change was inspired by https://reviews.llvm.org/D62443

[sbc100]

• cleanup

[sbc100]

• cleanup

[sbc100]

• cleanup

[sunfish]

Cool, this is nicer than my version :-).

[ruiu]

lld/trunk/wasm/Config.h

62

IIRC, the iteration order of StringSet is different between 32-bit and 64-bit hosts. That's bad for build reproducibility because even if all input files, command line options, and the linker versions are the same, two lld executables create different binaries if one is a 32-bit executable and the other is 64-bit one.

I'd use llvm/ADT/SetVector, which guarantees the iteration order.

lld/trunk/wasm/SymbolTable.cpp

202

This function seems a little tricky. Can you expand the comment? I believe the intended behavior is this:

Add a symbol with a given name if there's an undefined symbol with the same name. If we are exporting all symbols, a symbol is added unconditionally.

[sbc100]

lld/trunk/wasm/Config.h

62

We don't actually iterate over this set, we only test for presence symbol names.

lld/trunk/wasm/SymbolTable.cpp

202

Yes, you are correct. I will add a comment.

lld/trunk/test/wasm/alias.ll

 ; CHECK-NEXT:   - Type:            GLOBAL
 ; CHECK-NEXT:     Globals:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         true
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66560
-; CHECK-NEXT:       - Index:           1
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           66560
-; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1024
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            start_alias
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:   - Type:            CODE
 ; CHECK-NEXT:     Functions:

lld/trunk/test/wasm/archive-export.ll

 Test that --export will also fetch lazy symbols from archives
 
 RUN: llc -filetype=obj %S/Inputs/start.ll -o %t.o
 RUN: llc -filetype=obj %S/Inputs/archive1.ll -o %t.a1.o
 RUN: llc -filetype=obj %S/Inputs/archive2.ll -o %t.a2.o
 RUN: rm -f %t.a
 RUN: llvm-ar rcs %t.a %t.a1.o %t.a2.o
 RUN: wasm-ld --export-dynamic --export=archive2_symbol -o %t.wasm %t.a %t.o
 RUN: obj2yaml %t.wasm | FileCheck %s
 RUN: wasm-ld --export-dynamic -o %t.wasm %t.a %t.o
 RUN: obj2yaml %t.wasm | FileCheck %s -check-prefix=NOEXPORT
 
 CHECK:         Exports:
 CHECK-NEXT:       - Name:            memory
 CHECK-NEXT:         Kind:            MEMORY
 CHECK-NEXT:         Index:           0
-CHECK-NEXT:       - Name:            __heap_base
-CHECK-NEXT:         Kind:            GLOBAL
-CHECK-NEXT:         Index:           1
-CHECK-NEXT:       - Name:            __data_end
-CHECK-NEXT:         Kind:            GLOBAL
-CHECK-NEXT:         Index:           2
 CHECK-NEXT:       - Name:            foo
 CHECK-NEXT:         Kind:            FUNCTION
 CHECK-NEXT:         Index:           1
 CHECK-NEXT:       - Name:            bar
 CHECK-NEXT:         Kind:            FUNCTION
 CHECK-NEXT:         Index:           2
 CHECK-NEXT:       - Name:            archive2_symbol
 CHECK-NEXT:         Kind:            FUNCTION
 CHECK-NEXT:         Index:           3
 CHECK-NEXT:       - Name:            _start
 CHECK-NEXT:         Kind:            FUNCTION
 CHECK-NEXT:         Index:           0
 CHECK-NEXT:   - Type:            CODE
 
 NOEXPORT:         Exports:
 NOEXPORT-NEXT:       - Name:            memory
 NOEXPORT-NEXT:         Kind:            MEMORY
 NOEXPORT-NEXT:         Index:           0
-NOEXPORT-NEXT:       - Name:            __heap_base
-NOEXPORT-NEXT:         Kind:            GLOBAL
-NOEXPORT-NEXT:         Index:           1
-NOEXPORT-NEXT:       - Name:            __data_end
-NOEXPORT-NEXT:         Kind:            GLOBAL
-NOEXPORT-NEXT:         Index:           2
 NOEXPORT-NEXT:       - Name:            _start
 NOEXPORT-NEXT:         Kind:            FUNCTION
 NOEXPORT-NEXT:         Index:           0
 NOEXPORT-NEXT:   - Type:            CODE

lld/trunk/test/wasm/call-indirect.ll

 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66576
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           66576
-; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1036
-; CHECK-NEXT:       - Index:           3
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1032
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            bar
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            call_bar_indirect
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            foo
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           3
 ; CHECK-NEXT:       - Name:            indirect_func
 ; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           3
+; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            call_ptr
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           4
 ; CHECK-NEXT:   - Type:            ELEM
 ; CHECK-NEXT:     Segments:
 ; CHECK-NEXT:       - Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1

lld/trunk/test/wasm/comdats.ll

 ; CHECK-NEXT:        InitExpr:
 ; CHECK-NEXT:          Opcode:          I32_CONST
 ; CHECK-NEXT:          Value:           66576
 ; CHECK-NEXT:      - Index:           1
 ; CHECK-NEXT:        Type:            I32
 ; CHECK-NEXT:        Mutable:         false
 ; CHECK-NEXT:        InitExpr:
 ; CHECK-NEXT:          Opcode:          I32_CONST
-; CHECK-NEXT:          Value:           66576
-; CHECK-NEXT:      - Index:           2
-; CHECK-NEXT:        Type:            I32
-; CHECK-NEXT:        Mutable:         false
-; CHECK-NEXT:        InitExpr:
-; CHECK-NEXT:          Opcode:          I32_CONST
-; CHECK-NEXT:          Value:           1027
-; CHECK-NEXT:      - Index:           3
-; CHECK-NEXT:        Type:            I32
-; CHECK-NEXT:        Mutable:         false
-; CHECK-NEXT:        InitExpr:
-; CHECK-NEXT:          Opcode:          I32_CONST
 ; CHECK-NEXT:          Value:           1024
 ; CHECK-NEXT:  - Type:            EXPORT
 ; CHECK-NEXT:    Exports:
 ; CHECK-NEXT:      - Name:            memory
 ; CHECK-NEXT:        Kind:            MEMORY
 ; CHECK-NEXT:        Index:           0
-; CHECK-NEXT:      - Name:            __heap_base
-; CHECK-NEXT:        Kind:            GLOBAL
-; CHECK-NEXT:        Index:           1
-; CHECK-NEXT:      - Name:            __data_end
-; CHECK-NEXT:        Kind:            GLOBAL
-; CHECK-NEXT:        Index:           2
 ; CHECK-NEXT:      - Name:            _start
 ; CHECK-NEXT:        Kind:            FUNCTION
 ; CHECK-NEXT:        Index:           0
 ; CHECK-NEXT:      - Name:            inlineFn
 ; CHECK-NEXT:        Kind:            FUNCTION
 ; CHECK-NEXT:        Index:           1
 ; CHECK-NEXT:      - Name:            constantData
 ; CHECK-NEXT:        Kind:            GLOBAL
-; CHECK-NEXT:        Index:           3
+; CHECK-NEXT:        Index:           1
 ; CHECK-NEXT:      - Name:            callInline1
 ; CHECK-NEXT:        Kind:            FUNCTION
 ; CHECK-NEXT:        Index:           2
 ; CHECK-NEXT:      - Name:            callInline2
 ; CHECK-NEXT:        Kind:            FUNCTION
 ; CHECK-NEXT:        Index:           3
 ; CHECK-NEXT:  - Type:            ELEM
 ; CHECK-NEXT:    Segments:

lld/trunk/test/wasm/cxx-mangling.ll

define void @_start() {
   ret void
 }
 
 ; CHECK:        - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            _Z3fooi
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:   - Type:            CODE
 ; CHECK-NEXT:     Functions:

lld/trunk/test/wasm/data-layout.ll

 ; RUN: llc -filetype=obj %p/Inputs/hello.ll -o %t.hello.o
 ; RUN: llc -filetype=obj %s -o %t.o
 
 target triple = "wasm32-unknown-unknown"
 
 @foo = hidden global i32 1, align 4
 @aligned_bar = hidden global i32 3, align 16
 
 @hello_str = external global i8*
 @external_ref = global i8** @hello_str, align 8
 
 %struct.s = type { i32, i32 }
 @local_struct = hidden global %struct.s zeroinitializer, align 4
 @local_struct_internal_ptr = hidden local_unnamed_addr global i32* getelementptr inbounds (%struct.s, %struct.s* @local_struct, i32 0, i32 1), align 4
 
-; RUN: wasm-ld -no-gc-sections --allow-undefined --no-entry -o %t.wasm %t.o %t.hello.o
+; RUN: wasm-ld -no-gc-sections --export=__data_end --export=__heap_base --allow-undefined --no-entry -o %t.wasm %t.o %t.hello.o
 ; RUN: obj2yaml %t.wasm | FileCheck %s
 
 ; CHECK:        - Type:            MEMORY
 ; CHECK-NEXT:     Memories:
 ; CHECK-NEXT:       - Initial:         0x00000002
 ; CHECK-NEXT:   - Type:            GLOBAL
 ; CHECK-NEXT:     Globals:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         true
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66608
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           1071
+; CHECK-NEXT:       - Index:           2
+; CHECK-NEXT:         Type:            I32
+; CHECK-NEXT:         Mutable:         false
+; CHECK-NEXT:         InitExpr:
+; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66608
 
-; CHECK:         - Type:            DATA
+; CHECK:        - Type:            DATA
 ; CHECK-NEXT:     Segments:
 ; CHECK-NEXT:       - SectionOffset:   7
 ; CHECK-NEXT:         InitFlags:       0
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1024
 ; CHECK-NEXT:         Content:         '0100000000000000000000000000000003000000000000002804000024040000'
 ; CHECK-NEXT:       - SectionOffset:   45

lld/trunk/test/wasm/entry.ll

 ; RUN: wasm-ld --entry=entry -o %t2.wasm %t.o
 ; RUN: obj2yaml %t2.wasm | FileCheck %s
 
 ; CHECK:        - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            entry
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:   - Type:
 
 ; The __wasm_call_ctors is somewhat special since its created by the linker.
 ; Make sure we can use it as the entry point if we choose
 ; RUN: wasm-ld --entry=__wasm_call_ctors -o %t3.wasm %t.o
 ; RUN: obj2yaml %t3.wasm | FileCheck %s -check-prefix=CHECK-CTOR
 
 ; CHECK-CTOR:        - Type:            EXPORT
 ; CHECK-CTOR-NEXT:     Exports:
 ; CHECK-CTOR-NEXT:       - Name:            memory
 ; CHECK-CTOR-NEXT:         Kind:            MEMORY
 ; CHECK-CTOR-NEXT:         Index:           0
 ; CHECK-CTOR-NEXT:       - Name:            __wasm_call_ctors
 ; CHECK-CTOR-NEXT:         Kind:            FUNCTION
 ; CHECK-CTOR-NEXT:         Index:           0
-; CHECK-CTOR-NEXT:       - Name:            __heap_base
-; CHECK-CTOR-NEXT:         Kind:            GLOBAL
-; CHECK-CTOR-NEXT:         Index:           1
-; CHECK-CTOR-NEXT:       - Name:            __data_end
-; CHECK-CTOR-NEXT:         Kind:            GLOBAL
-; CHECK-CTOR-NEXT:         Index:           2
 ; CHECK-CTOR-NEXT:   - Type:

lld/trunk/test/wasm/export.ll

 
 ; CHECK-NOT: - Name: default_function
 
 ; CHECK:        - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            hidden_function
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            used_function
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:   - Type:            CODE

lld/trunk/test/wasm/local-symbols.ll

 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66576
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           66576
-; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1032
-; CHECK-NEXT:       - Index:           3
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1024
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            foo
 ; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           3
+; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:   - Type:            CODE
 ; CHECK-NEXT:     Functions:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Locals:
 ; CHECK-NEXT:         Body:            4100280284888080000B
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Locals:
 ; CHECK-NEXT:         Body:            1080808080001A0B

lld/trunk/test/wasm/locals-duplicate.test

 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66592
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           66592
-; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1048
-; CHECK-NEXT:       - Index:           3
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1028
-; CHECK-NEXT:       - Index:           4
+; CHECK-NEXT:       - Index:           2
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1036
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            colliding_func2
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            get_global1A
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           3
 ; CHECK-NEXT:       - Name:            get_global2A
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           4
 ; CHECK-NEXT:       - Name:            colliding_global2
 ; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           3
+; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            get_global3A
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           5
 ; CHECK-NEXT:       - Name:            get_func1A
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           6
 ; CHECK-NEXT:       - Name:            get_func2A
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           7
 ; CHECK-NEXT:       - Name:            get_func3A
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           8
 ; CHECK-NEXT:       - Name:            colliding_func1
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           9
 ; CHECK-NEXT:       - Name:            get_global1B
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           12
 ; CHECK-NEXT:       - Name:            colliding_global1
 ; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           4
+; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            get_global2B
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           13
 ; CHECK-NEXT:       - Name:            get_global3B
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           14
 ; CHECK-NEXT:       - Name:            get_func1B
 ; CHECK-NEXT:         Kind:            FUNCTION

lld/trunk/test/wasm/lto/export.ll

 
 ; CHECK-ERROR: error: symbol exported via --export not found: missing
 
 ; CHECK:        - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            hidden_function
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:   - Type:            CODE

lld/trunk/test/wasm/stack-first.test

 ; Test that the --stack-first option places the stack at the start of linear
 ; memory.  In this case the --stack-first option is being passed along with a
 ; stack size of 512.  This means (since the stack grows down) the stack pointer
 ; global should be initialized to 512.
 
 RUN: llc -filetype=obj %p/Inputs/start.ll -o %t.o
-
-RUN: wasm-ld -z stack-size=512 --stack-first --allow-undefined -o %t.wasm %t.o
+RUN: wasm-ld -z stack-size=512 --stack-first --export=__data_end --export=__heap_base -o %t.wasm %t.o
 RUN: obj2yaml %t.wasm | FileCheck %s
 
 CHECK:        - Type:            GLOBAL
 CHECK-NEXT:     Globals:         
 CHECK-NEXT:       - Index:           0
 CHECK-NEXT:         Type:            I32
 CHECK-NEXT:         Mutable:         true
 CHECK-NEXT:         InitExpr:        

 CHECK-NEXT:         InitExpr:        
 CHECK-NEXT:           Opcode:          I32_CONST
 CHECK-NEXT:           Value:           512
 CHECK-NEXT:   - Type:            EXPORT
 CHECK-NEXT:     Exports:         
 CHECK-NEXT:       - Name:            memory
 CHECK-NEXT:         Kind:            MEMORY
 CHECK-NEXT:         Index:           0
-CHECK-NEXT:       - Name:            __heap_base
+CHECK-NEXT:       - Name:            __data_end
 CHECK-NEXT:         Kind:            GLOBAL
 CHECK-NEXT:         Index:           1
-CHECK-NEXT:       - Name:            __data_end
+CHECK-NEXT:       - Name:            __heap_base
 CHECK-NEXT:         Kind:            GLOBAL
 CHECK-NEXT:         Index:           2
-
+CHECK-NEXT:       - Name:            _start
+CHECK-NEXT:         Kind:            FUNCTION
+CHECK-NEXT:         Index:           0

lld/trunk/test/wasm/undefined-weak-call.ll

 ; CHECK-NEXT:   - Type:            GLOBAL
 ; CHECK-NEXT:     Globals:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         true
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66560
-; CHECK-NEXT:       - Index:           1
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           66560
-; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1024
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            callWeakFuncs
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           3
 ; CHECK-NEXT:   - Type:            CODE
 ; CHECK-NEXT:     Functions:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Locals:
 ; CHECK-NEXT:         Body:            000B

lld/trunk/test/wasm/visibility-hidden.ll

entry:
   ret void
 }
 
 ; CHECK:        - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            objectDefault
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            archiveDefault
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           4
 ; CHECK-NEXT:   - Type:
 
 
 ; NO-DEFAULT:        - Type:            EXPORT
 ; NO-DEFAULT-NEXT:     Exports:
 ; NO-DEFAULT-NEXT:       - Name:            memory
 ; NO-DEFAULT-NEXT:         Kind:            MEMORY
 ; NO-DEFAULT-NEXT:         Index:           0
-; NO-DEFAULT-NEXT:       - Name:            __heap_base
-; NO-DEFAULT-NEXT:         Kind:            GLOBAL
-; NO-DEFAULT-NEXT:         Index:           1
-; NO-DEFAULT-NEXT:       - Name:            __data_end
-; NO-DEFAULT-NEXT:         Kind:            GLOBAL
-; NO-DEFAULT-NEXT:         Index:           2
 ; NO-DEFAULT-NEXT:       - Name:            _start
 ; NO-DEFAULT-NEXT:         Kind:            FUNCTION
 ; NO-DEFAULT-NEXT:         Index:           2
 ; NO-DEFAULT-NEXT:   - Type:

lld/trunk/test/wasm/weak-alias-overide.ll

 ; CHECK-NEXT:   - Type:            GLOBAL
 ; CHECK-NEXT:     Globals:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         true
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66560
-; CHECK-NEXT:       - Index:           1
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           66560
-; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1024
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            alias_fn
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            direct_fn
 ; CHECK-NEXT:         Kind:            FUNCTION

lld/trunk/test/wasm/weak-alias.ll

 ; CHECK-NEXT:   - Type:            GLOBAL
 ; CHECK-NEXT:     Globals:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         true
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66560
-; CHECK-NEXT:       - Index:           1
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           66560
-; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1024
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            alias_fn
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            direct_fn
 ; CHECK-NEXT:         Kind:            FUNCTION

lld/trunk/test/wasm/weak-symbols.ll

 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66576
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           66576
-; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1028
-; CHECK-NEXT:       - Index:           3
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1024
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            weakFn
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            exportWeak1
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            weakGlobal
 ; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           3
+; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            exportWeak2
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           3
 ; CHECK-NEXT:   - Type:            ELEM
 ; CHECK-NEXT:     Segments:
 ; CHECK-NEXT:       - Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1

lld/trunk/test/wasm/weak-undefined.ll

 ; CHECK-NEXT:   - Type:            GLOBAL
 ; CHECK-NEXT:     Globals:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         true
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           66560
-; CHECK-NEXT:       - Index:           1
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           66560
-; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Type:            I32
-; CHECK-NEXT:         Mutable:         false
-; CHECK-NEXT:         InitExpr:
-; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1024
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:       - Name:            __heap_base
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           1
-; CHECK-NEXT:       - Name:            __data_end
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:   - Type:            CODE
 ; CHECK-NEXT:     Functions:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Locals:
 ; CHECK-NEXT:         Body:            4180808080000B
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Locals:
 ; CHECK-NEXT:         Body:            4180808080000B
 ; CHECK-NEXT:       - Index:           2
 ; CHECK-NEXT:         Locals:
 ; CHECK-NEXT:         Body:            1081808080001A1080808080001A0B
 ; CHECK-NEXT: ...

lld/trunk/wasm/Config.h

struct Configuration {
   unsigned Optimize;
   unsigned ThinLTOJobs;
 
   llvm::StringRef Entry;
   llvm::StringRef OutputFile;
   llvm::StringRef ThinLTOCacheDir;
 
   llvm::StringSet<> AllowUndefinedSymbols;
+  llvm::StringSet<> ExportedSymbols;
   std::vector<llvm::StringRef> SearchPaths;
   llvm::CachePruningPolicy ThinLTOCachePolicy;
   llvm::Optional<std::vector<std::string>> Features;
 
   // The following config options do not directly correspond to any
   // particualr command line options.
 
   // True if we are creating position-independent code.

lld/trunk/wasm/Driver.cpp

if (Config->Shared) {
     auto *StackPointer = make<InputGlobal>(Global, nullptr);
     StackPointer->Live = true;
     // For non-PIC code
     // TODO(sbc): Remove WASM_SYMBOL_VISIBILITY_HIDDEN when the mutable global
     // spec proposal is implemented in all major browsers.
     // See: https://github.com/WebAssembly/mutable-global
     WasmSym::StackPointer = Symtab->addSyntheticGlobal(
         "__stack_pointer", WASM_SYMBOL_VISIBILITY_HIDDEN, StackPointer);
-    WasmSym::HeapBase = Symtab->addSyntheticDataSymbol("__heap_base", 0);
-    WasmSym::DataEnd = Symtab->addSyntheticDataSymbol("__data_end", 0);
-
-    // These two synthetic symbols exist purely for the embedder so we always
-    // want to export them.
-    WasmSym::HeapBase->ForceExport = true;
-    WasmSym::DataEnd->ForceExport = true;
+    WasmSym::DataEnd = Symtab->addOptionalDataSymbol("__data_end");
+    WasmSym::HeapBase = Symtab->addOptionalDataSymbol("__heap_base");
   }
 
   if (Config->Pic) {
     // For PIC code, we import two global variables (__memory_base and
     // __table_base) from the environment and use these as the offset at
     // which to load our static data and function table.
     // See:
     // https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md
if (!Args.hasArg(OPT_INPUT)) {
     error("no input files");
     return;
   }
 
   // Handle --trace-symbol.
   for (auto *Arg : Args.filtered(OPT_trace_symbol))
     Symtab->trace(Arg->getValue());
 
+  for (auto *Arg : Args.filtered(OPT_export))
+    Config->ExportedSymbols.insert(Arg->getValue());
+
   if (!Config->Relocatable)
     createSyntheticSymbols();
 
   createFiles(Args);
   if (errorCount())
     return;
 
   // Add all files to the symbol table. This will add almost all
   // symbols that we need to the symbol table.
   for (InputFile *F : Files)
     Symtab->addFile(F);
   if (errorCount())
     return;
 
   // Handle the `--undefined <sym>` options.
   for (auto *Arg : Args.filtered(OPT_undefined))
     handleUndefined(Arg->getValue());
 
+  // Handle the `--export <sym>` options
+  // This works like --undefined but also exports the symbol if its found
+  for (auto *Arg : Args.filtered(OPT_export))
+    handleUndefined(Arg->getValue());
+
   Symbol *EntrySym = nullptr;
   if (!Config->Relocatable && !Config->Entry.empty()) {
     EntrySym = handleUndefined(Config->Entry);
     if (EntrySym && EntrySym->isDefined())
       EntrySym->ForceExport = true;
     else
       error("entry symbol not defined (pass --no-entry to supress): " +
             Config->Entry);
   }
 
   if (errorCount())
     return;
 
-  // Handle the `--export <sym>` options
-  // This works like --undefined but also exports the symbol if its found
-  for (auto *Arg : Args.filtered(OPT_export))
-    handleUndefined(Arg->getValue());
-
   // Create wrapped symbols for -wrap option.
   std::vector<WrappedSymbol> Wrapped = addWrappedSymbols(Args);
 
   // Do link-time optimization if given files are LLVM bitcode files.
   // This compiles bitcode files into real object files.
   Symtab->addCombinedLTOObject();
   if (errorCount())
     return;

lld/trunk/wasm/SymbolTable.h

public:
 
   bool addComdat(StringRef Name);
 
   DefinedData *addSyntheticDataSymbol(StringRef Name, uint32_t Flags);
   DefinedGlobal *addSyntheticGlobal(StringRef Name, uint32_t Flags,
                                     InputGlobal *Global);
   DefinedFunction *addSyntheticFunction(StringRef Name, uint32_t Flags,
                                         InputFunction *Function);
-  DefinedData *addOptionalDataSymbol(StringRef Name, uint32_t Value,
-                                     uint32_t Flags);
+  DefinedData *addOptionalDataSymbol(StringRef Name, uint32_t Value = 0,
+                                     uint32_t Flags = 0);
 
   void handleSymbolVariants();
   void handleWeakUndefines();
 
   std::vector<ObjFile *> ObjectFiles;
   std::vector<SharedFile *> SharedFiles;
   std::vector<BitcodeFile *> BitcodeFiles;
   std::vector<InputFunction *> SyntheticFunctions;

lld/trunk/wasm/SymbolTable.cpp

DefinedFunction *SymbolTable::addSyntheticFunction(StringRef Name,
                                                    InputFunction *Function) {
   LLVM_DEBUG(dbgs() << "addSyntheticFunction: " << Name << "\n");
   assert(!find(Name));
   SyntheticFunctions.emplace_back(Function);
   return replaceSymbol<DefinedFunction>(insertName(Name).first, Name,
                                         Flags, nullptr, Function);
 }
 
 DefinedData *SymbolTable::addOptionalDataSymbol(StringRef Name, uint32_t Value,
                                                 uint32_t Flags) {
   Symbol *S = find(Name);
-  if (!S || S->isDefined())
+  // Enable --export of optional symbols
+  if (!S && (Config->ExportAll || Config->ExportedSymbols.count(Name) != 0))
+    S = insertName(Name).first;
+  else if (!S || S->isDefined())
     return nullptr;
   LLVM_DEBUG(dbgs() << "addOptionalDataSymbol: " << Name << "\n");
   auto *rtn = replaceSymbol<DefinedData>(S, Name, Flags);
   rtn->setVirtualAddress(Value);
   return rtn;
 }
 
 DefinedData *SymbolTable::addSyntheticDataSymbol(StringRef Name,

lld/trunk/wasm/Writer.cpp

void Writer::layoutMemory() {
   }
 
   if (!Config->StackFirst)
     PlaceStack();
 
   // Set `__heap_base` to directly follow the end of the stack or global data.
   // The fact that this comes last means that a malloc/brk implementation
   // can grow the heap at runtime.
-  if (!Config->Relocatable) {
-    WasmSym::HeapBase->setVirtualAddress(MemoryPtr);
-    log("mem: heap base   = " + Twine(MemoryPtr));
-  }
+  if (WasmSym::HeapBase)
+    WasmSym::HeapBase->setVirtualAddress(MemoryPtr);
 
   if (Config->InitialMemory != 0) {
     if (Config->InitialMemory != alignTo(Config->InitialMemory, WasmPageSize))
       error("initial memory must be " + Twine(WasmPageSize) + "-byte aligned");
     if (MemoryPtr > Config->InitialMemory)
       error("initial memory too small, " + Twine(MemoryPtr) + " bytes needed");
     else
       MemoryPtr = Config->InitialMemory;

 // gold provide the feature, and used by many programs.
 void Writer::addStartStopSymbols(const InputSegment *Seg) {
   StringRef S = Seg->getName();
   LLVM_DEBUG(dbgs() << "addStartStopSymbols: " << S << "\n");
   if (!isValidCIdentifier(S))
     return;
   uint32_t Start = Seg->OutputSeg->StartVA + Seg->OutputSegmentOffset;
   uint32_t Stop = Start + Seg->getSize();
-  Symtab->addOptionalDataSymbol(Saver.save("__start_" + S), Start, 0);
-  Symtab->addOptionalDataSymbol(Saver.save("__stop_" + S), Stop, 0);
+  Symtab->addOptionalDataSymbol(Saver.save("__start_" + S), Start);
+  Symtab->addOptionalDataSymbol(Saver.save("__stop_" + S), Stop);
 }
 
 void Writer::addSections() {
   addSection(Out.DylinkSec);
   addSection(Out.TypeSec);
   addSection(Out.ImportSec);
   addSection(Out.FunctionSec);
   addSection(Out.TableSec);