[WebAssembly] Always start table index at 1, even for relocatable output

[ncw]

Summary

Previously llvm was using 0 as the first table index for wasm object files
but now that has switched to 1 we can have the output of lld do the same
and simplify the code.

---

No need to commit simultaneously with the matching LLVM change (D42095), they are completely independent. Third chunk split out of D41955.

No functional changes, since the table is ignored of object files.

[ncw]

test/wasm/relocatable.ll

132

Test expectations updated: as for D42095, relocatable Wasm files now match non-relocatable ones (avoiding random/unnecessary differences between them is good). The ELEM section has offset one, causing the indexes below to be incremented by one as well.

[sbc100]

wasm/Writer.cpp

111

Just use a global static "static const int kInitialTableOffset"?

[ncw]

Updated:

• Renamed constant

[ncw]

Updated:

• Simple rebase

[ncw]

Updated:

• Another rebase after #4c and #4d landed

[ncw]

Updated:

• Rebased to avoid conflict after previous change was landed with some reformating

[sbc100]

Can you update the description and title, now that this change is so specific.

[ncw]

Updated:

• After weak-alias.ll test was extended (to test relocatable output as well) this patch had to be updated...

Could it be merged soon to avoid further rebasing?

[sbc100]

I was imagining a more simple CL description. Something like:

[WebAssembly] Always start table index at 1, even for relocatable output

Previously llvm was using 0 as the first table index for wasm object files
but now that has switched to 1 we can have the output of lld to the same
and simply the code.

Happy to land make this change myself as I land it but i think its nice to have
the review match the commit.

test/wasm/relocatable.ll

 ; CHECK-NEXT:         GlobalMutable:   false
 ; CHECK-NEXT:   - Type:            FUNCTION
 ; CHECK-NEXT:     FunctionTypes:   [ 0, 2, 2 ]
 ; CHECK-NEXT:   - Type:            TABLE
 ; CHECK-NEXT:     Tables:
 ; CHECK-NEXT:       - ElemType:        ANYFUNC
 ; CHECK-NEXT:         Limits:
 ; CHECK-NEXT:           Flags:           [ HAS_MAX ]
-; CHECK-NEXT:           Initial:         0x00000002
-; CHECK-NEXT:           Maximum:         0x00000002
+; CHECK-NEXT:           Initial:         0x00000003
+; CHECK-NEXT:           Maximum:         0x00000003
 ; CHECK-NEXT:   - Type:            MEMORY
 ; CHECK-NEXT:     Memories:
 ; CHECK-NEXT:       - Initial:         0x00000001
 ; CHECK-NEXT:   - Type:            GLOBAL
 ; CHECK-NEXT:     Globals:
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false

 ; CHECK-NEXT:         Index:           4
 ; CHECK-NEXT:       - Name:            data_addr1
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         Index:           5
 ; CHECK-NEXT:   - Type:            ELEM
 ; CHECK-NEXT:     Segments:
 ; CHECK-NEXT:       - Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           0
+; CHECK-NEXT:           Value:           1
 ; CHECK-NEXT:         Functions:       [ 3, 1 ]
 ; CHECK-NEXT:   - Type:            CODE
 ; CHECK-NEXT:     Relocations:
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_SLEB
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:         Offset:          0x00000004
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_FUNCTION_INDEX_LEB
 ; CHECK-NEXT:         Index:           0

 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           0
 ; CHECK-NEXT:         Content:         68656C6C6F0A00
 ; CHECK-NEXT:       - SectionOffset:   18
 ; CHECK-NEXT:         MemoryIndex:     0
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           8
-; CHECK-NEXT:         Content:         '00000000'
+; CHECK-NEXT:         Content:         '01000000'
 ; CHECK-NEXT:       - SectionOffset:   27
 ; CHECK-NEXT:         MemoryIndex:     0
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           12
-; CHECK-NEXT:         Content:         '01000000'
+; CHECK-NEXT:         Content:         '02000000'
 ; CHECK-NEXT:       - SectionOffset:   36
 ; CHECK-NEXT:         MemoryIndex:     0
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           16
 ; CHECK-NEXT:         Content:         '00000000'
 ; CHECK-NEXT:       - SectionOffset:   45
 ; CHECK-NEXT:         MemoryIndex:     0

wasm/Writer.cpp

private:
   void createNameSection();
 
   void writeHeader();
   void writeSections();
 
   uint64_t FileSize = 0;
   uint32_t DataSize = 0;
   uint32_t NumMemoryPages = 0;
-  uint32_t InitialTableOffset = 0;
+  uint32_t InitialTableOffset = 1;
 
   std::vector<const WasmSignature *> Types;
   DenseMap<WasmSignature, int32_t, WasmSignatureDenseMapInfo> TypeIndices;
   std::vector<const Symbol *> ImportedFunctions;
   std::vector<const Symbol *> ImportedGlobals;
   std::vector<const Symbol *> DefinedGlobals;
   std::vector<InputFunction *> DefinedFunctions;
   std::vector<const Symbol *> IndirectFunctions;
void Writer::calculateInitFunctions() {
   // in the correct order.
   std::sort(InitFunctions.begin(), InitFunctions.end(),
             [](const WasmInitFunc &L, const WasmInitFunc &R) {
               return L.Priority < R.Priority;
             });
 }
 
 void Writer::run() {
-  if (!Config->Relocatable)
-    InitialTableOffset = 1;
-
   log("-- calculateTypes");
   calculateTypes();
   log("-- calculateImports");
   calculateImports();
   log("-- assignIndexes");
   assignIndexes();
   log("-- calculateInitFunctions");
   calculateInitFunctions();