[LoongArch] Make the code generation of the trap pattern configurable

[heiher]

Relevant GCC patch: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=15c8169ec55b52630ab884dd7a30c3237ada98b2

[llvmbot]

@llvm/pr-subscribers-backend-loongarch

Author: hev (heiher)

Changes

Relevant GCC patch: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=15c8169ec55b52630ab884dd7a30c3237ada98b2

---

Full diff: https://github.com/llvm/llvm-project/pull/166913.diff

4 Files Affected:

• (modified) llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp (+24-1)
• (modified) llvm/lib/Target/LoongArch/LoongArchISelLowering.h (+2)
• (modified) llvm/lib/Target/LoongArch/LoongArchInstrInfo.td (+14-5)
• (modified) llvm/test/CodeGen/LoongArch/trap.ll (+19-6)

diff --git a/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp b/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
index cf4ffc82f6009..f3b725c731a95 100644
--- a/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
+++ b/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
@@ -74,6 +74,13 @@ static cl::opt<bool> ZeroDivCheck("loongarch-check-zero-division", cl::Hidden,
                                   cl::desc("Trap on integer division by zero."),
                                   cl::init(false));
 
+static cl::opt<int> TrapBreakCode("loongarch-trap-break-code", cl::init(-1),
+                                  cl::desc("Use 'break CODE' for traps "
+                                           "supposed to be unrecoverable, "
+                                           "or an 'amswap.w' instruction "
+                                           "leading to INE if CODE is out "
+                                           "of range."));
+
 LoongArchTargetLowering::LoongArchTargetLowering(const TargetMachine &TM,
                                                  const LoongArchSubtarget &STI)
     : TargetLowering(TM), Subtarget(STI) {
@@ -125,7 +132,7 @@ LoongArchTargetLowering::LoongArchTargetLowering(const TargetMachine &TM,
   setOperationAction({ISD::VAARG, ISD::VACOPY, ISD::VAEND}, MVT::Other, Expand);
 
   setOperationAction(ISD::DEBUGTRAP, MVT::Other, Legal);
-  setOperationAction(ISD::TRAP, MVT::Other, Legal);
+  setOperationAction(ISD::TRAP, MVT::Other, Custom);
 
   setOperationAction(ISD::INTRINSIC_VOID, MVT::Other, Custom);
   setOperationAction(ISD::INTRINSIC_W_CHAIN, MVT::Other, Custom);
@@ -610,10 +617,25 @@ SDValue LoongArchTargetLowering::LowerOperation(SDValue Op,
     return lowerVECREDUCE(Op, DAG);
   case ISD::ConstantFP:
     return lowerConstantFP(Op, DAG);
+  case ISD::TRAP:
+    return lowerTrap(Op, DAG);
   }
   return SDValue();
 }
 
+SDValue LoongArchTargetLowering::lowerTrap(SDValue Op,
+                                           SelectionDAG &DAG) const {
+  SDLoc DL(Op);
+  SDValue Chain = Op.getOperand(0);
+
+  if (isUInt<15>(TrapBreakCode))
+    return DAG.getNode(
+        LoongArchISD::BREAK, DL, MVT::Other, Chain,
+        DAG.getConstant(TrapBreakCode, DL, Subtarget.getGRLenVT()));
+
+  return DAG.getNode(LoongArchISD::UNIMP, DL, MVT::Other, Chain);
+}
+
 SDValue LoongArchTargetLowering::lowerConstantFP(SDValue Op,
                                                  SelectionDAG &DAG) const {
   EVT VT = Op.getValueType();
@@ -7500,6 +7522,7 @@ const char *LoongArchTargetLowering::getTargetNodeName(unsigned Opcode) const {
     NODE_NAME_CASE(TAIL)
     NODE_NAME_CASE(TAIL_MEDIUM)
     NODE_NAME_CASE(TAIL_LARGE)
+    NODE_NAME_CASE(UNIMP)
     NODE_NAME_CASE(SELECT_CC)
     NODE_NAME_CASE(BR_CC)
     NODE_NAME_CASE(BRCOND)
diff --git a/llvm/lib/Target/LoongArch/LoongArchISelLowering.h b/llvm/lib/Target/LoongArch/LoongArchISelLowering.h
index 8a4d7748467c7..86682d4b9e9e6 100644
--- a/llvm/lib/Target/LoongArch/LoongArchISelLowering.h
+++ b/llvm/lib/Target/LoongArch/LoongArchISelLowering.h
@@ -33,6 +33,7 @@ enum NodeType : unsigned {
   TAIL,
   TAIL_MEDIUM,
   TAIL_LARGE,
+  UNIMP,
 
   // Select
   SELECT_CC,
@@ -415,6 +416,7 @@ class LoongArchTargetLowering : public TargetLowering {
   SDValue lowerVECREDUCE_ADD(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerVECREDUCE(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerConstantFP(SDValue Op, SelectionDAG &DAG) const;
+  SDValue lowerTrap(SDValue Op, SelectionDAG &DAG) const;
 
   bool isFPImmLegal(const APFloat &Imm, EVT VT,
                     bool ForCodeSize) const override;
diff --git a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td
index 9565a55e4c6c5..72cda642d0546 100644
--- a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td
+++ b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td
@@ -97,6 +97,8 @@ def loongarch_call_large : SDNode<"LoongArchISD::CALL_LARGE", SDT_LoongArchCall,
 def loongarch_tail_large : SDNode<"LoongArchISD::TAIL_LARGE", SDT_LoongArchCall,
                                   [SDNPHasChain, SDNPOptInGlue, SDNPOutGlue,
                                    SDNPVariadic]>;
+def loongarch_unimp : SDNode<"LoongArchISD::UNIMP", SDTypeProfile<0, 0, []>,
+                             [SDNPHasChain, SDNPSideEffect]>;
 def loongarch_selectcc : SDNode<"LoongArchISD::SELECT_CC", SDT_LoongArchSelectCC>;
 def loongarch_brcc : SDNode<"LoongArchISD::BR_CC", SDT_LoongArchBrCC,
                             [SDNPHasChain]>;
@@ -1373,11 +1375,18 @@ def : Pat<(and GPR:$rj, BstrinsImm:$imm),
 
 /// Traps
 
-// We lower `trap` to `amswap.w rd:$r0, rk:$r1, rj:$r0`, as this is guaranteed
-// to trap with an INE (non-existent on LA32, explicitly documented to INE on
-// LA64). And the resulting signal is different from `debugtrap` like on some
-// other existing ports so programs/porters might have an easier time.
-def PseudoUNIMP : Pseudo<(outs), (ins), [(trap)]>,
+// ISD::TRAP is lowered to either LoongArchISD::UNIMP or LoongArchISD::BREAK
+// depending on the --loongarch-trap-break-code=<N> option (default: -1).
+// - If N is a valid 15-bit unsigned integer (0 <= N <= 32767), it expands to
+//   LoongArchISD::BREAK N, producing a BREAK instruction with the specified
+//   code.
+// - Otherwise, it expands to LoongArchISD::UNIMP.
+
+// We lower `loongarch_unimp` to `amswap.w rd:$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), [(loongarch_unimp)]>,
                   PseudoInstExpansion<(AMSWAP_W R0, R1, R0)>;
 
 // We lower `debugtrap` to `break 0`, as this is guaranteed to exist and work,
diff --git a/llvm/test/CodeGen/LoongArch/trap.ll b/llvm/test/CodeGen/LoongArch/trap.ll
index 15a7ad82bd7a8..434807207f63d 100644
--- a/llvm/test/CodeGen/LoongArch/trap.ll
+++ b/llvm/test/CodeGen/LoongArch/trap.ll
@@ -1,6 +1,14 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc --mtriple=loongarch32 -mattr=+d --verify-machineinstrs < %s | FileCheck %s
-; RUN: llc --mtriple=loongarch64 -mattr=+d --verify-machineinstrs < %s | FileCheck %s
+; RUN: llc --mtriple=loongarch32 -mattr=+d --verify-machineinstrs < %s | \
+; RUN:   FileCheck %s --check-prefixes=CHECK,CHECK-AMSWAP
+; RUN: llc --mtriple=loongarch32 -mattr=+d --verify-machineinstrs \
+; RUN:   --loongarch-trap-break-code=1 < %s | \
+; RUN:   FileCheck %s --check-prefixes=CHECK,CHECK-BREAK
+; RUN: llc --mtriple=loongarch64 -mattr=+d --verify-machineinstrs < %s | \
+; RUN:   FileCheck %s --check-prefixes=CHECK,CHECK-AMSWAP
+; RUN: llc --mtriple=loongarch64 -mattr=+d --verify-machineinstrs \
+; RUN:   --loongarch-trap-break-code=1 < %s | \
+; RUN:   FileCheck %s --check-prefixes=CHECK,CHECK-BREAK
 
 ;; Verify that we lower @llvm.trap() and @llvm.debugtrap() correctly.
 
@@ -8,10 +16,15 @@ 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
+; CHECK-AMSWAP-LABEL: test_trap:
+; CHECK-AMSWAP:       # %bb.0:
+; CHECK-AMSWAP-NEXT:    amswap.w $zero, $ra, $zero
+; CHECK-AMSWAP-NEXT:    ret
+;
+; CHECK-BREAK-LABEL: test_trap:
+; CHECK-BREAK:       # %bb.0:
+; CHECK-BREAK-NEXT:    break 1
+; CHECK-BREAK-NEXT:    ret
   tail call void @llvm.trap()
   ret void
 }

[heiher]

cc @xry111 @xen0n

[heiher]

Should we make Clang support a GCC-style -mbreak-code= flag? This flag obviously doesn't work with rustc. For such a niche need, I suggest we have both Clang and rustc use: --llvm --loongarch-trap-break-code=<N>.