[WebAssembly] Fix Fast ISEL not lowering 64-bit function pointers

[tlively]

llvm/test/CodeGen/WebAssembly/fast-isel-call-indirect64.ll

14–22

This test function could be stripped down even more.

[aardappel]

simplified test

llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp

if (IsDirect) {
     // Ensure that the object file has a __indirect_function_table import, as we
     // call_indirect against it.
     MCSymbolWasm *Sym = WebAssembly::getOrCreateFunctionTableSymbol(
         MF->getMMI().getContext(), "__indirect_function_table");
     // Until call_indirect emits TABLE_NUMBER relocs against this symbol, mark
     // it as NO_STRIP so as to ensure that the indirect function table makes it
     // to linked output.
     Sym->setNoStrip();
+
+    // See if we must truncate the function pointer.
+    // CALL_INDIRECT takes an i32, but in wasm64 we represent function pointers
+    // as 64-bit for uniformity with other pointer types.
+    // See also: WebAssemblyISelLowering.cpp: LowerCallResults
+    if (Subtarget->hasAddr64()) {
+      auto Wrap = BuildMI(*FuncInfo.MBB, std::prev(FuncInfo.InsertPt), DbgLoc,
+                          TII.get(WebAssembly::I32_WRAP_I64));
+      unsigned Reg32 = createResultReg(&WebAssembly::I32RegClass);
+      Wrap.addReg(Reg32, RegState::Define);
+      Wrap.addReg(CalleeReg);
+      CalleeReg = Reg32;
+    }
   }
 
   for (unsigned ArgReg : Args)
     MIB.addReg(ArgReg);
 
   if (!IsDirect)
     MIB.addReg(CalleeReg);
 

llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp

static MachineBasicBlock *LowerCallResults(MachineInstr &CallResults,
 
   MachineFunction &MF = *BB->getParent();
   const MCInstrDesc &MCID = TII.get(CallOp);
   MachineInstrBuilder MIB(MF, MF.CreateMachineInstr(MCID, DL));
 
   // See if we must truncate the function pointer.
   // CALL_INDIRECT takes an i32, but in wasm64 we represent function pointers
   // as 64-bit for uniformity with other pointer types.
+  // See also: WebAssemblyFastISel::selectCall
   if (IsIndirect && MF.getSubtarget<WebAssemblySubtarget>().hasAddr64()) {
     Register Reg32 =
         MF.getRegInfo().createVirtualRegister(&WebAssembly::I32RegClass);
     auto &FnPtr = CallParams.getOperand(0);
     BuildMI(*BB, CallResults.getIterator(), DL,
             TII.get(WebAssembly::I32_WRAP_I64), Reg32)
         .addReg(FnPtr.getReg());
     FnPtr.setReg(Reg32);

llvm/test/CodeGen/WebAssembly/fast-isel-call-indirect64.ll

+; RUN: llc < %s -fast-isel --mtriple=wasm64 -asm-verbose=false -wasm-keep-registers | FileCheck %s
+
+target datalayout = "e-m:e-p:64:64-i64:64-n32:64-S128"
+target triple = "wasm64"
+
+; Ensure fast isel also lowers function pointers to 32-bit.
+
+; CHECK:       local.get $push[[L0:[0-9]+]]=, 0
+; CHECK-NEXT:  i32.wrap_i64 $push[[L1:[0-9]+]]=, $pop[[L0]]
+; CHECK-NEXT:  call_indirect $pop[[L1]]
+
+define hidden void @f(void ()* %g) {
+  call void %g()
+  ret void
+}