[SelectionDAG] Not issue TRAP node if naked function

llvm/include/llvm/IR/Instructions.h

@@ -4497,6 +4497,9 @@ class UnreachableInst : public Instruction {
     return isa<Instruction>(V) && classof(cast<Instruction>(V));
   }
 
+  // Whether to do target lowering in SelectionDAG.
+  bool shouldLowerToTrap(bool TrapUnreachable, bool NoTrapAfterNoreturn) const;
+
 private:
   BasicBlock *getSuccessor(unsigned idx) const {
     llvm_unreachable("UnreachableInst has no successors!");

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

@@ -3143,21 +3143,12 @@ bool IRTranslator::translateVAArg(const User &U, MachineIRBuilder &MIRBuilder) {
   return true;
 }
 
-bool IRTranslator::translateUnreachable(const User &U, MachineIRBuilder &MIRBuilder) {
-  if (!MF->getTarget().Options.TrapUnreachable)
-    return true;
-
+bool IRTranslator::translateUnreachable(const User &U,
+                                        MachineIRBuilder &MIRBuilder) {
   auto &UI = cast<UnreachableInst>(U);
-
-  // We may be able to ignore unreachable behind a noreturn call.
-  if (const CallInst *Call = dyn_cast_or_null<CallInst>(UI.getPrevNode());
-      Call && Call->doesNotReturn()) {
-    if (MF->getTarget().Options.NoTrapAfterNoreturn)
-      return true;
-    // Do not emit an additional trap instruction.
-    if (Call->isNonContinuableTrap())
-      return true;
-  }
+  if (!UI.shouldLowerToTrap(MF->getTarget().Options.TrapUnreachable,
+                            MF->getTarget().Options.NoTrapAfterNoreturn))
+    return true;
 
   MIRBuilder.buildTrap();
   return true;

llvm/lib/CodeGen/SelectionDAG/FastISel.cpp

@@ -1854,17 +1854,12 @@ bool FastISel::selectOperator(const User *I, unsigned Opcode) {
   }
 
   case Instruction::Unreachable: {
-    if (TM.Options.TrapUnreachable) {
-      if (TM.Options.NoTrapAfterNoreturn) {
-        const auto *Call =
-            dyn_cast_or_null<CallInst>(cast<Instruction>(I)->getPrevNode());
-        if (Call && Call->doesNotReturn())
-          return true;
-      }
+    auto UI = cast<UnreachableInst>(I);
+    if (!UI->shouldLowerToTrap(TM.Options.TrapUnreachable,
+                               TM.Options.NoTrapAfterNoreturn))
+      return true;
 
-      return fastEmit_(MVT::Other, MVT::Other, ISD::TRAP) != 0;
-    }
-    return true;
+    return fastEmit_(MVT::Other, MVT::Other, ISD::TRAP) != 0;
   }
 
   case Instruction::Alloca:

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -3501,19 +3501,10 @@ void SelectionDAGBuilder::visitIndirectBr(const IndirectBrInst &I) {
 }
 
 void SelectionDAGBuilder::visitUnreachable(const UnreachableInst &I) {
-  if (!DAG.getTarget().Options.TrapUnreachable)
+  if (!I.shouldLowerToTrap(DAG.getTarget().Options.TrapUnreachable,
+                           DAG.getTarget().Options.NoTrapAfterNoreturn))
     return;
 
-  // We may be able to ignore unreachable behind a noreturn call.
-  if (const CallInst *Call = dyn_cast_or_null<CallInst>(I.getPrevNode());
-      Call && Call->doesNotReturn()) {
-    if (DAG.getTarget().Options.NoTrapAfterNoreturn)
-      return;
-    // Do not emit an additional trap instruction.
-    if (Call->isNonContinuableTrap())
-      return;
-  }
-
   DAG.setRoot(DAG.getNode(ISD::TRAP, getCurSDLoc(), MVT::Other, DAG.getRoot()));
 }
 

llvm/lib/IR/Instructions.cpp

@@ -4529,6 +4529,27 @@ UnreachableInst *UnreachableInst::cloneImpl() const {
   return new UnreachableInst(Context);
 }
 
+bool UnreachableInst::shouldLowerToTrap(bool TrapUnreachable,
+                                        bool NoTrapAfterNoreturn) const {
+  if (!TrapUnreachable)
+    return false;
+
+  // We may be able to ignore unreachable behind a noreturn call.
+  if (const CallInst *Call = dyn_cast_or_null<CallInst>(getPrevNode());
+      Call && Call->doesNotReturn()) {
+    if (NoTrapAfterNoreturn)
+      return false;
+    // Do not emit an additional trap instruction.
+    if (Call->isNonContinuableTrap())
+      return false;
+  }
+
+  if (getFunction()->hasFnAttribute(Attribute::Naked))
+    return false;
+
+  return true;
+}
+
 FreezeInst *FreezeInst::cloneImpl() const {
   return new FreezeInst(getOperand(0));
 }

llvm/test/CodeGen/WebAssembly/naked-fn-with-frame-pointer.ll

@@ -9,13 +9,11 @@ define dso_local void @naked() naked "frame-pointer"="all" {
 ; CHECK-32:         .functype naked () -> ()
 ; CHECK-32-NEXT:  # %bb.0:
 ; CHECK-32-NEXT:    call main
-; CHECK-32-NEXT:    unreachable
 ;
 ; CHECK-64-LABEL: naked:
 ; CHECK-64:         .functype naked () -> ()
 ; CHECK-64-NEXT:  # %bb.0:
 ; CHECK-64-NEXT:    call main
-; CHECK-64-NEXT:    unreachable
   call void @main()
   unreachable
 }

llvm/test/CodeGen/X86/naked-fn-with-unreachable-trap.ll

@@ -0,0 +1,11 @@
+; RUN: llc -o - %s -mtriple=x86_64-linux-gnu -trap-unreachable | FileCheck %s
+; RUN: llc -o - %s -mtriple=x86_64-linux-gnu -trap-unreachable -fast-isel | FileCheck %s
+
+define dso_local void @foo() #0 {
+entry:
+  tail call void asm sideeffect "movl 3,%eax", "~{dirflag},~{fpsr},~{flags}"()
+  unreachable
+}
+; CHECK-NOT: ud2
+
+attributes #0 = { naked }