This patch is to fix radar://8426430. It is about llvm support of __builtin_debugtrap()

which is supposed to consistently raise SIGTRAP across all systems. In contrast,
__builtin_trap() behave differently on different systems. e.g. it raises SIGTRAP on ARM, and
SIGILL on X86. The purpose of __builtin_debugtrap() is to consistently provide "trap"
functionality, in the mean time preserve the compatibility with on gcc on __builtin_trap().

  The X86 backend is already able to handle debugtrap(). This patch is to:
  1) make front-end recognize "__builtin_debugtrap()" (emboddied in the one-line change to Clang).
  2) In DAG legalization phase, by default, "debugtrap" will be replaced with "trap", which
     make the __builtin_debugtrap() "available" to all existing ports without the hassle of
     changing their code.
  3) If trap-function is specified (via -trap-func=xyz to llc), both __builtin_debugtrap() and
     __builtin_trap() will be expanded into the function call of the specified trap function.
    This behavior may need change in the future.

  The provided testing-case is to make sure 2) and 3) are working for ARM port, and we
already have a testing case for x86. 


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166300 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Intrinsics.td

@@ -420,7 +420,7 @@ def int_flt_rounds : Intrinsic<[llvm_i32_ty]>,
                      GCCBuiltin<"__builtin_flt_rounds">;
 def int_trap : Intrinsic<[], [], [IntrNoReturn]>,
                GCCBuiltin<"__builtin_trap">;
-def int_debugtrap : Intrinsic<[]>,
+def int_debugtrap : Intrinsic<[], [], [IntrNoReturn]>,
                     GCCBuiltin<"__builtin_debugtrap">;
 
 // NOP: calls/invokes to this intrinsic are removed by codegen

lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

@@ -1240,6 +1240,19 @@ void SelectionDAGLegalize::LegalizeOp(SDNode *Node) {
     if (Action == TargetLowering::Legal)
       Action = TargetLowering::Custom;
     break;
+  case ISD::DEBUGTRAP:
+    Action = TLI.getOperationAction(Node->getOpcode(), Node->getValueType(0));
+    if (Action == TargetLowering::Expand) {
+      // replace ISD::DEBUGTRAP with ISD::TRAP
+      SDValue NewVal;
+      NewVal = DAG.getNode (ISD::TRAP, Node->getDebugLoc(), Node->getVTList(),
+                            Node->getOperand(0));
+      ReplaceNode(Node, NewVal.getNode());
+      LegalizeOp(NewVal.getNode());
+      return;
+    }
+    break;
+
   default:
     if (Node->getOpcode() >= ISD::BUILTIN_OP_END) {
       Action = TargetLowering::Legal;

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -5175,10 +5175,13 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
     return 0;
   }
 
+  case Intrinsic::debugtrap:
   case Intrinsic::trap: {
     StringRef TrapFuncName = TM.Options.getTrapFunctionName();
     if (TrapFuncName.empty()) {
-      DAG.setRoot(DAG.getNode(ISD::TRAP, dl,MVT::Other, getRoot()));
+      ISD::NodeType Op = (Intrinsic == Intrinsic::trap) ? 
+        ISD::TRAP : ISD::DEBUGTRAP;
+      DAG.setRoot(DAG.getNode(Op, dl,MVT::Other, getRoot()));
       return 0;
     }
     TargetLowering::ArgListTy Args;
@@ -5193,10 +5196,7 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
     DAG.setRoot(Result.second);
     return 0;
   }
-  case Intrinsic::debugtrap: {
-    DAG.setRoot(DAG.getNode(ISD::DEBUGTRAP, dl,MVT::Other, getRoot()));
-    return 0;
-  }
+
   case Intrinsic::uadd_with_overflow:
   case Intrinsic::sadd_with_overflow:
   case Intrinsic::usub_with_overflow:

lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -583,6 +583,11 @@ TargetLowering::TargetLowering(const TargetMachine &tm,
   // Default ISD::TRAP to expand (which turns it into abort).
   setOperationAction(ISD::TRAP, MVT::Other, Expand);
 
+  // On most systems, DEBUGTRAP and TRAP have no difference. The "Expand"
+  // here is to inform DAG Legalizer to replace DEBUGTRAP with TRAP.
+  //
+  setOperationAction(ISD::DEBUGTRAP, MVT::Other, Expand);
+
   IsLittleEndian = TD->isLittleEndian();
   PointerTy = MVT::getIntegerVT(8*TD->getPointerSize(0));
   memset(RegClassForVT, 0,MVT::LAST_VALUETYPE*sizeof(TargetRegisterClass*));

lib/Target/X86/X86ISelLowering.cpp

@@ -557,6 +557,7 @@ X86TargetLowering::X86TargetLowering(X86TargetMachine &TM)
   setOperationAction(ISD::ADJUST_TRAMPOLINE, MVT::Other, Custom);
 
   setOperationAction(ISD::TRAP, MVT::Other, Legal);
+  setOperationAction(ISD::DEBUGTRAP, MVT::Other, Legal);
 
   // VASTART needs to be custom lowered to use the VarArgsFrameIndex
   setOperationAction(ISD::VASTART           , MVT::Other, Custom);

test/CodeGen/ARM/trap.ll

@@ -14,4 +14,16 @@ entry:
   unreachable
 }
 
+define void @t2() nounwind {
+entry:
+; INSTR: t2:
+; INSTR: trap
+
+; FUNC: t2:
+; FUNC: bl __trap
+  call void @llvm.debugtrap()
+  unreachable
+}
+
 declare void @llvm.trap() nounwind
+declare void @llvm.debugtrap() nounwind