[llvm] [WebAssembly] Support parsing .lto_set_conditional (PR #126546)

[Sam Clegg via llvm-commits]

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@@ -1817,7 +1817,18 @@ uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
       assert(WasmIndices.count(&WS) > 0);
       Info.ElementIndex = WasmIndices.find(&WS)->second;
     } else if (WS.isDefined()) {
-      assert(DataLocations.count(&WS) > 0);
+      if (!DataLocations.count(&WS))
+        // In bitcode generated by split-LTO-unit mode in ThinLTO, these lines
+        // can appear:
+        // module asm ".lto_set_conditional symbolA,symbolA.[moduleId]"
+        // ...
+        // (Here [moduleId] will be replaced by a real module hash ID)
+        //
+        // Here the original symbols (symbolA here) have been renamed to symbol
+        // new names created by attaching their module IDs and the original
+        // symbols do not appear in the bitcode anymore, and thus not in
+        // DataLocations. We should ignore them.
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sbc100 wrote:

I wonder if we should instead add an early return right that top of this function (before `LLVM_DEBUG(dbgs() << "adding to symtab: " << WS << "\n");`).

Something like:

`if (WS.isData() && !DataLocations.count(&WS)) contionue`

Or maybe we could have `isInSymtab` return false for these symbols which is already handled with a continue above.

https://github.com/llvm/llvm-project/pull/126546