[WebAssembly] Fix symbol type for addresses of external functions

[sbc100]

Summary

These symbols were previously not being marked as functions
so were apprering as globals instead, and with the incorrect
relocation type.

Without this fix, objects that take address of external
functions include them as global imports rather than function
imports which then fails at link time.

[sunfish]

LGTM

llvm/trunk/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

 #include "llvm/CodeGen/MachineConstantPool.h"
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbol.h"
+#include "llvm/MC/MCSymbolWasm.h"
+#include "llvm/MC/MCSymbolELF.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "asm-printer"
 
 //===----------------------------------------------------------------------===//
default: {
     EmitToStreamer(*OutStreamer, TmpInst);
     break;
   }
   }
 }
 
 const MCExpr *WebAssemblyAsmPrinter::lowerConstant(const Constant *CV) {
   if (const GlobalValue *GV = dyn_cast<GlobalValue>(CV))
-    if (GV->getValueType()->isFunctionTy())
+    if (GV->getValueType()->isFunctionTy()) {
+      MCSymbol* Sym = getSymbol(GV);
+      if (!isa<MCSymbolELF>(Sym))
+        cast<MCSymbolWasm>(Sym)->setIsFunction(true);
       return MCSymbolRefExpr::create(
-          getSymbol(GV), MCSymbolRefExpr::VK_WebAssembly_FUNCTION, OutContext);
+          Sym, MCSymbolRefExpr::VK_WebAssembly_FUNCTION, OutContext);
+    }
   return AsmPrinter::lowerConstant(CV);
 }
 
 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
                                             unsigned OpNo, unsigned AsmVariant,
                                             const char *ExtraCode,
                                             raw_ostream &OS) {
   if (AsmVariant != 0)

llvm/trunk/test/MC/WebAssembly/external-data.ll

 ; RUN: llc -mtriple wasm32-unknown-unknown-wasm -filetype=obj %s -o - | obj2yaml | FileCheck %s
 ; Verify relocations are correctly generated for addresses of externals
 ; in the data section.
 
-declare i32 @f1(...)
+@myimport = external global i32, align 4
 
 @foo = global i64 7, align 4
-@far = local_unnamed_addr global i32 (...)* @f1, align 4
+@bar = hidden global i32* @myimport, align 4
 
 ; CHECK:   - Type:            DATA
 ; CHECK:     Relocations:
 ; CHECK:       - Type:            R_WEBASSEMBLY_GLOBAL_ADDR_I32
 ; CHECK:         Index:           0
 ; CHECK:         Offset:          0x0000000E
 ; CHECK:     Segments:
 ; CHECK:       - Index:           0
 ; CHECK:         Offset:
 ; CHECK:           Opcode:          I32_CONST
 ; CHECK:           Value:           0
 ; CHECK:         Content:         0700000000000000FFFFFFFF
 

llvm/trunk/test/MC/WebAssembly/external-func-address.ll

+; RUN: llc -mtriple wasm32-unknown-unknown-wasm -filetype=obj %s -o - | obj2yaml | FileCheck %s
+; Verify that addresses of external functions generate correctly typed
+; imports and relocations or type R_TABLE_INDEX_I32.
+
+declare void @f1() #1
+@ptr_to_f1 = hidden global void ()* @f1, align 4
+
+
+; CHECK:   - Type:            IMPORT
+; CHECK:     Imports:
+; CHECK:       - Module:          env
+; CHECK:         Field:           f1
+; CHECK:         Kind:            FUNCTION
+; CHECK:         SigIndex:        0
+; CHECK:   - Type:            ELEM
+; CHECK:     Segments:
+; CHECK:       - Offset:
+; CHECK:           Opcode:          I32_CONST
+; CHECK:           Value:           0
+; CHECK:         Functions:       [ 0 ]
+; CHECK:   - Type:            DATA
+; CHECK:     Relocations:
+; CHECK:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_I32
+; CHECK:         Index:           0
+; CHECK:         Offset:          0x00000006