[RISCV] Lower llvm.trap and llvm.debugtrap

Summary:
Until this commit, these have lowered to a call to abort().

`llvm.trap()` now lowers to `unimp`, which should trap on all systems.

`llvm.debugtrap()` now lowers to `ebreak`, which is exactly what this
instruction is for.

Reviewers: asb, luismarques

Reviewed By: asb

Subscribers: hiraditya, rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, kito-cheng, shiva0217, jrtc27, MaskRay, zzheng, edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe, PkmX, jocewei, psnobl, benna, Jim, s.egerton, pzheng, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69390

3 files changed, 51 insertions, 0 deletions

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index b67d4a85c32..4058af7328c 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -193,6 +193,9 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
   setOperationAction(ISD::READCYCLECOUNTER, MVT::i64,
                      Subtarget.is64Bit() ? Legal : Custom);
 
+  setOperationAction(ISD::TRAP, MVT::Other, Legal);
+  setOperationAction(ISD::DEBUGTRAP, MVT::Other, Legal);
+
   if (Subtarget.hasStdExtA()) {
     setMaxAtomicSizeInBitsSupported(Subtarget.getXLen());
     setMinCmpXchgSizeInBits(32);
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfo.td b/llvm/lib/Target/RISCV/RISCVInstrInfo.td
index db2ecc49d14..aaddecdc7d2 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfo.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfo.td
@@ -1097,6 +1097,16 @@ let Predicates = [IsRV32], usesCustomInserter = 1, hasSideEffects = 0,
 mayLoad = 0, mayStore = 0, hasNoSchedulingInfo = 1 in
 def ReadCycleWide : Pseudo<(outs GPR:$lo, GPR:$hi), (ins), [], "", "">;
 
+/// traps
+
+// We lower `trap` to `unimp`, as this causes a hard exception on nearly all
+// systems.
+def : Pat<(trap), (UNIMP)>;
+
+// We lower `debugtrap` to `ebreak`, as this will get the attention of the
+// debugger if possible.
+def : Pat<(debugtrap), (EBREAK)>;
+
 //===----------------------------------------------------------------------===//
 // Standard extensions
 //===----------------------------------------------------------------------===//
diff --git a/llvm/test/CodeGen/RISCV/intrinsics/trap.ll b/llvm/test/CodeGen/RISCV/intrinsics/trap.ll
new file mode 100644
index 00000000000..e85073518ab
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/intrinsics/trap.ll
@@ -0,0 +1,38 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv32 -verify-machineinstrs < %s \
+; RUN:   | FileCheck -check-prefix=RV32I %s
+; RUN: llc -mtriple=riscv64 -verify-machineinstrs < %s \
+; RUN:   | FileCheck -check-prefix=RV64I %s
+
+; Verify that we lower @llvm.trap() and @llvm.debugtrap() correctly.
+
+declare void @llvm.trap()
+declare void @llvm.debugtrap()
+
+define void @test_trap() nounwind {
+; RV32I-LABEL: test_trap:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    unimp
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: test_trap:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    unimp
+; RV64I-NEXT:    ret
+  tail call void @llvm.trap()
+  ret void
+}
+
+define void @test_debugtrap() nounwind {
+; RV32I-LABEL: test_debugtrap:
+; RV32I:       # %bb.0:
+; RV32I-NEXT:    ebreak
+; RV32I-NEXT:    ret
+;
+; RV64I-LABEL: test_debugtrap:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    ebreak
+; RV64I-NEXT:    ret
+  tail call void @llvm.debugtrap()
+  ret void
+}