[WebAssembly] Fix function return type printing

[dschuff]

Summary

Previously return type information for a function was derived from
return dag nodes. But this didn't work for dags with != return node. So
instead compute it directly from the LLVM function as is done for imports.

[sunfish]

Looks good. This kind of begs the question of whether we should do this for the params too (and maybe further refactor the logic about multiple results after lowering), but I'm ok leaving that for later here.

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

149

LLVM style puts the reference by the var, rather than the type.

lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h

52–74

You can delete the Results field itself too.

[dschuff]

Rebase, address comments

[dschuff]

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

void WebAssemblyAsmPrinter::EmitConstantPool() {
   assert(MF->getConstantPool()->getConstants().empty() &&
          "WebAssembly disables constant pools");
 }
 
 void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
   // Nothing to do; jump tables are incorporated into the instruction stream.
 }
 
+static void ComputeLegalValueVTs(const Function &F,
+                                 const TargetMachine &TM,
+                                 Type *Ty,
+                                 SmallVectorImpl<MVT> &ValueVTs) {
+  const DataLayout& DL(F.getParent()->getDataLayout());
+  const WebAssemblyTargetLowering &TLI =
+      *TM.getSubtarget<WebAssemblySubtarget>(F).getTargetLowering();
+  SmallVector<EVT, 4> VTs;
+  ComputeValueVTs(TLI, DL, Ty, VTs);
+
+  for (EVT VT : VTs) {
+    unsigned NumRegs = TLI.getNumRegisters(F.getContext(), VT);
+    MVT RegisterVT = TLI.getRegisterType(F.getContext(), VT);
+    for (unsigned i = 0; i != NumRegs; ++i)
+      ValueVTs.push_back(RegisterVT);
+  }
+}
+
 void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
   SmallString<128> Str;
   raw_svector_ostream OS(Str);
 
   for (MVT VT : MFI->getParams())
     OS << "\t" ".param " << toString(VT) << '\n';
-  for (MVT VT : MFI->getResults())
-    OS << "\t" ".result " << toString(VT) << '\n';
+
+  SmallVector<MVT, 4> ResultVTs;
+  const Function &F(*MF->getFunction());
+  ComputeLegalValueVTs(F, TM, F.getReturnType(), ResultVTs);
+  // If the return type needs to be legalized it will get converted into
+  // passing a pointer.
+  if (ResultVTs.size() == 1)
+    OS << "\t" ".result " << toString(ResultVTs.front()) << '\n';
 
   bool FirstVReg = true;
   for (unsigned Idx = 0, IdxE = MRI->getNumVirtRegs(); Idx != IdxE; ++Idx) {
     unsigned VReg = TargetRegisterInfo::index2VirtReg(Idx);
     if (!MRI->use_empty(VReg)) {
       if (FirstVReg)
         OS << "\t" ".local ";
       else
default: {
     MCInst TmpInst;
     MCInstLowering.Lower(MI, TmpInst);
     EmitToStreamer(*OutStreamer, TmpInst);
     break;
   }
   }
 }
 
-static void ComputeLegalValueVTs(LLVMContext &Context,
-                                 const WebAssemblyTargetLowering &TLI,
-                                 const DataLayout &DL, Type *Ty,
-                                 SmallVectorImpl<MVT> &ValueVTs) {
-  SmallVector<EVT, 4> VTs;
-  ComputeValueVTs(TLI, DL, Ty, VTs);
 
-  for (EVT VT : VTs) {
-    unsigned NumRegs = TLI.getNumRegisters(Context, VT);
-    MVT RegisterVT = TLI.getRegisterType(Context, VT);
-    for (unsigned i = 0; i != NumRegs; ++i)
-      ValueVTs.push_back(RegisterVT);
-  }
-}
 
 void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
   const DataLayout &DL = M.getDataLayout();
 
   SmallString<128> Str;
   raw_svector_ostream OS(Str);
   for (const Function &F : M)
     if (F.isDeclarationForLinker()) {
       assert(F.hasName() && "imported functions must have a name");
       if (F.isIntrinsic())
         continue;
       if (Str.empty())
         OS << "\t.imports\n";
 
       MCSymbol *Sym = OutStreamer->getContext().getOrCreateSymbol(F.getName());
       OS << "\t.import " << *Sym << " \"\" " << *Sym;
 
       const WebAssemblyTargetLowering &TLI =
           *TM.getSubtarget<WebAssemblySubtarget>(F).getTargetLowering();
 
       // If we need to legalize the return type, it'll get converted into
       // passing a pointer.
       bool SawParam = false;
       SmallVector<MVT, 4> ResultVTs;
-      ComputeLegalValueVTs(M.getContext(), TLI, DL, F.getReturnType(),
-                           ResultVTs);
+      ComputeLegalValueVTs(F, TM, F.getReturnType(), ResultVTs);
       if (ResultVTs.size() > 1) {
         ResultVTs.clear();
         OS << " (param " << toString(TLI.getPointerTy(DL));
         SawParam = true;
       }
 
       for (const Argument &A : F.args()) {
         SmallVector<MVT, 4> ParamVTs;
-        ComputeLegalValueVTs(M.getContext(), TLI, DL, A.getType(), ParamVTs);
-        for (EVT VT : ParamVTs) {
+        ComputeLegalValueVTs(F, TM, A.getType(), ParamVTs);
+        for (MVT VT : ParamVTs) {
           if (!SawParam) {
             OS << " (param";
             SawParam = true;
           }
-          OS << ' ' << toString(VT.getSimpleVT());
+          OS << ' ' << toString(VT);
         }
       }
       if (SawParam)
         OS << ')';
 
-      for (EVT VT : ResultVTs)
-        OS << " (result " << toString(VT.getSimpleVT()) << ')';
+      for (MVT VT : ResultVTs)
+        OS << " (result " << toString(VT) << ')';
 
       OS << '\n';
     }
 
   StringRef Text = OS.str();
   if (!Text.empty())
     OutStreamer->EmitRawText(Text.substr(0, Text.size() - 1));
 }

lib/Target/WebAssembly/WebAssemblyISelLowering.cpp

bool WebAssemblyTargetLowering::CanLowerReturn(
   return Outs.size() <= 1;
 }
 
 SDValue WebAssemblyTargetLowering::LowerReturn(
     SDValue Chain, CallingConv::ID CallConv, bool IsVarArg,
     const SmallVectorImpl<ISD::OutputArg> &Outs,
     const SmallVectorImpl<SDValue> &OutVals, SDLoc DL,
     SelectionDAG &DAG) const {
-  MachineFunction &MF = DAG.getMachineFunction();
-
   assert(Outs.size() <= 1 && "WebAssembly can only return up to one value");
   if (CallConv != CallingConv::C)
     fail(DL, DAG, "WebAssembly doesn't support non-C calling conventions");
   if (IsVarArg)
     fail(DL, DAG, "WebAssembly doesn't support varargs yet");
 
   SmallVector<SDValue, 4> RetOps(1, Chain);
   RetOps.append(OutVals.begin(), OutVals.end());
   Chain = DAG.getNode(WebAssemblyISD::RETURN, DL, MVT::Other, RetOps);
 
   // Record the number and types of the return values.
   for (const ISD::OutputArg &Out : Outs) {
     if (Out.Flags.isByVal())
       fail(DL, DAG, "WebAssembly hasn't implemented byval results");
     if (Out.Flags.isInAlloca())
       fail(DL, DAG, "WebAssembly hasn't implemented inalloca results");
     if (Out.Flags.isNest())
       fail(DL, DAG, "WebAssembly hasn't implemented nest results");
     if (Out.Flags.isInConsecutiveRegs())
       fail(DL, DAG, "WebAssembly hasn't implemented cons regs results");
     if (Out.Flags.isInConsecutiveRegsLast())
       fail(DL, DAG, "WebAssembly hasn't implemented cons regs last results");
     if (!Out.IsFixed)
       fail(DL, DAG, "WebAssembly doesn't support non-fixed results yet");
-    MF.getInfo<WebAssemblyFunctionInfo>()->addResult(Out.VT);
   }
 
   return Chain;
 }
 
 SDValue WebAssemblyTargetLowering::LowerFormalArguments(
     SDValue Chain, CallingConv::ID CallConv, bool IsVarArg,
     const SmallVectorImpl<ISD::InputArg> &Ins, SDLoc DL, SelectionDAG &DAG,

lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h

 namespace llvm {
 
 /// This class is derived from MachineFunctionInfo and contains private
 /// WebAssembly-specific information for each MachineFunction.
 class WebAssemblyFunctionInfo final : public MachineFunctionInfo {
   MachineFunction &MF;
 
   std::vector<MVT> Params;
-  std::vector<MVT> Results;
 
   /// A mapping from CodeGen vreg index to WebAssembly register number.
   std::vector<unsigned> WARegs;
 
   /// A mapping from CodeGen vreg index to a boolean value indicating whether
   /// the given register is considered to be "stackified", meaning it has been
   /// determined or made to meet the stack requirements:
   ///   - single use (per path)
   ///   - single def (per path)
   ///   - defined and used in FIFO order with other stack registers
   BitVector VRegStackified;
 
 public:
   explicit WebAssemblyFunctionInfo(MachineFunction &MF) : MF(MF) {}
   ~WebAssemblyFunctionInfo() override;
 
   void addParam(MVT VT) { Params.push_back(VT); }
   const std::vector<MVT> &getParams() const { return Params; }
 
-  void addResult(MVT VT) { Results.push_back(VT); }
-  const std::vector<MVT> &getResults() const { return Results; }
-
   static const unsigned UnusedReg = -1u;
 
   void stackifyVReg(unsigned VReg) {
     if (TargetRegisterInfo::virtReg2Index(VReg) >= VRegStackified.size())
       VRegStackified.resize(TargetRegisterInfo::virtReg2Index(VReg) + 1);
     VRegStackified.set(TargetRegisterInfo::virtReg2Index(VReg));
   }
   bool isVRegStackified(unsigned VReg) const {
     if (TargetRegisterInfo::virtReg2Index(VReg) >= VRegStackified.size())
       return false;
     return VRegStackified.test(TargetRegisterInfo::virtReg2Index(VReg));
   }
 
   void initWARegs();
   void setWAReg(unsigned VReg, unsigned WAReg) {
     assert(WAReg != UnusedReg);
     WARegs[TargetRegisterInfo::virtReg2Index(VReg)] = WAReg;
   }
   unsigned getWAReg(unsigned VReg) const {
     return WARegs[TargetRegisterInfo::virtReg2Index(VReg)];
   }
 };
 
 } // end namespace llvm
 
 #endif

test/CodeGen/WebAssembly/func.ll

 ; CHECK-NEXT: .param i32{{$}}
 ; CHECK-NEXT: .param f32{{$}}
 ; CHECK-NOT: .local
 ; CHECK-NEXT: return{{$}}
 ; CHECK: .size f3,
 define void @f3(i32 %p1, float %p2) {
   ret void
 }
+
+; CHECK-LABEL: f4:
+; CHECK-NEXT: .param i32{{$}}
+; CHECK-NEXT: .result i32{{$}}
+; CHECK-NEXT: .local
+define i32 @f4(i32 %x) {
+entry:
+   %c = trunc i32 %x to i1
+   br i1 %c, label %true, label %false
+true:
+   ret i32 0
+false:
+   ret i32 1
+}
+
+; CHECK-LABEL: f5:
+; CHECK-NEXT: .result f32{{$}}
+; CHECK-NEXT: unreachable
+define float @f5()  {
+ unreachable
+}