[WebAssembly] MC: Fix type of function aliases

[sbc100]

Summary

Aliases of functions are now marked as function symbols even if
they are bitcast to some other other non-function type.
This is important for WebAssembly where object and function
symbols can't alias each other.

Fixes PR38866

[sbc100]

add comment

[dschuff]

LGTM. Can you put a little more detail in the commit message (e.g. something like what you wrote in the comment) to make it easier to see in a log (without having to look at the code or the PR)?

[sbc100]

• Handle issue in AsmPrinter so MCSymbol has correct type

[sbc100]

• Update test

lib/MC/WasmObjectWriter.cpp

for (const MCSymbol &S : Asm.symbols()) {
     assert(S.isDefined());
 
     // Find the target symbol of this weak alias and export that index
     const auto &WS = static_cast<const MCSymbolWasm &>(S);
     const MCSymbolWasm *ResolvedSym = ResolveSymbol(WS);
     LLVM_DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *ResolvedSym
                       << "'\n");
 
-    if (WS.isFunction()) {
+    if (ResolvedSym->isFunction()) {
       assert(WasmIndices.count(ResolvedSym) > 0);
       uint32_t WasmIndex = WasmIndices.find(ResolvedSym)->second;
       WasmIndices[&WS] = WasmIndex;
       LLVM_DEBUG(dbgs() << "  -> index:" << WasmIndex << "\n");
     } else if (WS.isData()) {
       assert(DataLocations.count(ResolvedSym) > 0);
       const wasm::WasmDataReference &Ref =
           DataLocations.find(ResolvedSym)->second;
for (const MCSymbol &S : Asm.symbols()) {
     if (WS.isHidden())
       Flags |= wasm::WASM_SYMBOL_VISIBILITY_HIDDEN;
     if (!WS.isExternal() && WS.isDefined())
       Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL;
     if (WS.isUndefined())
       Flags |= wasm::WASM_SYMBOL_UNDEFINED;
 
     wasm::WasmSymbolInfo Info;
-    Info.Name = WS.getName();
+    bool isData = WS.isData();
+    if (WS.isVariable()) {
+      // For data symbols that are aliases of function symbols we override
+      // the type here so that the alias has the correct function type.
+      const MCSymbolWasm *ResolvedSym = ResolveSymbol(WS);
+      Info.Kind = ResolvedSym->getType();
+      isData = ResolvedSym->isData();
+    } else {
       Info.Kind = WS.getType();
+    }
+    Info.Name = WS.getName();
     Info.Flags = Flags;
-    if (!WS.isData()) {
+    if (!isData) {
       assert(WasmIndices.count(&WS) > 0);
       Info.ElementIndex = WasmIndices.find(&WS)->second;
     } else if (WS.isDefined()) {
       assert(DataLocations.count(&WS) > 0);
       Info.DataRef = DataLocations.find(&WS)->second;
     }
     WS.setIndex(SymbolInfos.size());
     SymbolInfos.emplace_back(Info);

test/MC/WebAssembly/function-alias.ll

+; RUN: llc -filetype=obj %s -o - | llvm-readobj -symbols | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown-wasm"
+
+@foo = alias i8, bitcast (void ()* @func to i8*)
+@bar = alias void (), void ()* @func
+
+define void @func() {
+  ret void
+}
+
+; CHECK:      Symbols [
+; CHECK-NEXT:   Symbol {
+; CHECK-NEXT:     Name: func
+; CHECK-NEXT:     Type: FUNCTION (0x0)
+; CHECK-NEXT:     Flags: 0x0
+; CHECK-NEXT:   }
+; CHECK-NEXT:   Symbol {
+; CHECK-NEXT:     Name: foo
+; CHECK-NEXT:     Type: FUNCTION (0x0)
+; CHECK-NEXT:     Flags: 0x0
+; CHECK-NEXT:   }
+; CHECK-NEXT:   Symbol {
+; CHECK-NEXT:     Name: bar
+; CHECK-NEXT:     Type: FUNCTION (0x0)
+; CHECK-NEXT:     Flags: 0x0
+; CHECK-NEXT:   }
+; CHECK-NEXT: ]