[LoongArch] Add support for llvm.trap and llvm.debugtrap

Similar to D69390 for RISCV, use a guaranteed non-existing insn for
llvm.trap and the break insn for llvm.debugtrap.

Differential Revision: https://reviews.llvm.org/D134365

llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp

@@ -57,6 +57,8 @@ LoongArchTargetLowering::LoongArchTargetLowering(const TargetMachine &TM,
   setOperationAction(ISD::FP_TO_SINT, GRLenVT, Custom);
   setOperationAction(ISD::ROTL, GRLenVT, Expand);
   setOperationAction(ISD::CTPOP, GRLenVT, Expand);
+  setOperationAction(ISD::DEBUGTRAP, MVT::Other, Legal);
+  setOperationAction(ISD::TRAP, MVT::Other, Legal);
 
   setOperationAction({ISD::GlobalAddress, ISD::BlockAddress, ISD::ConstantPool,
                       ISD::JumpTable},

llvm/lib/Target/LoongArch/LoongArchInstrInfo.td

@@ -742,6 +742,21 @@ def : Pat<(not (or GPR:$rj, GPR:$rk)), (NOR GPR:$rj, GPR:$rk)>;
 def : Pat<(or GPR:$rj, (not GPR:$rk)), (ORN GPR:$rj, GPR:$rk)>;
 def : Pat<(and GPR:$rj, (not GPR:$rk)), (ANDN GPR:$rj, GPR:$rk)>;
 
+/// Traps
+
+// We lower `trap` to `amswap.w rd:$r0, rk:$r1, rj:$r0`, as this is guaranteed
+// to trap with an INE (non-existent on LA32, explicitly documented to INE on
+// LA64). And the resulting signal is different from `debugtrap` like on some
+// other existing ports so programs/porters might have an easier time.
+def PseudoUNIMP : Pseudo<(outs), (ins), [(trap)]>,
+                  PseudoInstExpansion<(AMSWAP_W R0, R1, R0)>;
+
+// We lower `debugtrap` to `break 0`, as this is guaranteed to exist and work,
+// even for LA32 Primary. Also, because so far the ISA does not provide a
+// specific trap instruction/kind exclusively for alerting the debugger,
+// every other project uses the generic immediate of 0 for this.
+def : Pat<(debugtrap), (BREAK 0)>;
+
 /// Bit counting operations
 
 let Predicates = [IsLA64] in {

llvm/test/CodeGen/LoongArch/trap.ll

@@ -0,0 +1,26 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc --mtriple=loongarch32 --verify-machineinstrs < %s | FileCheck %s
+; RUN: llc --mtriple=loongarch64 --verify-machineinstrs < %s | FileCheck %s
+
+;; Verify that we lower @llvm.trap() and @llvm.debugtrap() correctly.
+
+declare void @llvm.trap()
+declare void @llvm.debugtrap()
+
+define void @test_trap() nounwind {
+; CHECK-LABEL: test_trap:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    amswap.w $zero, $ra, $zero
+; CHECK-NEXT:    ret
+  tail call void @llvm.trap()
+  ret void
+}
+
+define void @test_debugtrap() nounwind {
+; CHECK-LABEL: test_debugtrap:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    break 0
+; CHECK-NEXT:    ret
+  tail call void @llvm.debugtrap()
+  ret void
+}