[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/CodeGen/AsmPrinter/AsmPrinter.cpp

void AsmPrinter::emitGlobalIndirectSymbol(Module &M,
 
   if (GIS.hasExternalLinkage() || !MAI->getWeakRefDirective())
     OutStreamer->EmitSymbolAttribute(Name, MCSA_Global);
   else if (GIS.hasWeakLinkage() || GIS.hasLinkOnceLinkage())
     OutStreamer->EmitSymbolAttribute(Name, MCSA_WeakReference);
   else
     assert(GIS.hasLocalLinkage() && "Invalid alias or ifunc linkage");
 
+  bool isFunction = GIS.getType()->getPointerElementType()->isFunctionTy();
+
+  // Treat bitcasts of functions as functions also. This is important at least
+  // on WebAssembly where object and function addresses can't alias each other.
+  if (!isFunction)
+    if (auto *CE = dyn_cast<ConstantExpr>(GIS.getIndirectSymbol()))
+      if (CE->getOpcode() == Instruction::BitCast)
+        isFunction =
+          CE->getOperand(0)->getType()->getPointerElementType()->isFunctionTy();
+
+
   // Set the symbol type to function if the alias has a function type.
   // This affects codegen when the aliasee is not a function.
-  if (GIS.getType()->getPointerElementType()->isFunctionTy()) {
+  if (isFunction) {
     OutStreamer->EmitSymbolAttribute(Name, MCSA_ELF_TypeFunction);
     if (isa<GlobalIFunc>(GIS))
       OutStreamer->EmitSymbolAttribute(Name, MCSA_ELF_TypeIndFunction);
   }
 
   EmitVisibility(Name, GIS.getVisibility());
 
   const MCExpr *Expr = lowerConstant(GIS.getIndirectSymbol());

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 (i8* ()* @func to i8*)
+@bar = alias i8* (), i8* ()* @func
+
+define i8* @func() {
+  ret i8* @foo;
+}
+
+; 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: ]