[Statepoint Lowering] Fix the crash with gc.relocate lowering when it is in a separate block

[skatkov]

Summary

If it was decided to relocate derived pointer using the spill its value is
not exported in general case.
When gc.relocate is located in an another block than a statepoint we cannot
get SD for derived value but for spill case it is not required at all.
However implementation of gc.relocate lowering unconditionally request SD value
causing the assert triggering.

The CL fixes this by handling spill case earlier than SD is really required.

[dantrushin]

LGTM

llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp

1257

Could you check that SD.isUndef case will have NoRelocate record type too? If so, assert can be moved a bit higher.

llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp

if (Record.type == RecordType::VReg) {
     // chain with current root to ensure proper ordering of copies w.r.t.
     // statepoint.
     SDValue Chain = DAG.getRoot();
     SDValue Relocation = RFV.getCopyFromRegs(DAG, FuncInfo, getCurSDLoc(),
                                              Chain, nullptr, nullptr);
     setValue(&Relocate, Relocation);
     return;
   }
-  
-  SDValue SD = getValue(DerivedPtr);
-
-  if (SD.isUndef() && SD.getValueType().getSizeInBits() <= 64) {
-    // Lowering relocate(undef) as arbitrary constant. Current constant value
-    // is chosen such that it's unlikely to be a valid pointer.
-    setValue(&Relocate, DAG.getTargetConstant(0xFEFEFEFE, SDLoc(SD), MVT::i64));
-    return;
-  }
-
-
-  // We didn't need to spill these special cases (constants and allocas).
-  // See the handling in spillIncomingValueForStatepoint for detail.
-  if (Record.type == RecordType::NoRelocate) {
-    setValue(&Relocate, SD);
-    return;
-  }
-
-  assert(Record.type == RecordType::Spill);
-
-  unsigned Index = Record.payload.FI;;
+  if (Record.type == RecordType::Spill) {
+    unsigned Index = Record.payload.FI;
     SDValue SpillSlot = DAG.getTargetFrameIndex(Index, getFrameIndexTy());
 
     // All the reloads are independent and are reading memory only modified by
     // statepoints (i.e. no other aliasing stores); informing SelectionDAG of
-  // this this let's CSE kick in for free and allows reordering of instructions
-  // if possible.  The lowering for statepoint sets the root, so this is
-  // ordering all reloads with the either a) the statepoint node itself, or b)
-  // the entry of the current block for an invoke statepoint.
+    // this this let's CSE kick in for free and allows reordering of
+    // instructions if possible.  The lowering for statepoint sets the root,
+    // so this is ordering all reloads with the either
+    // a) the statepoint node itself, or
+    // b) the entry of the current block for an invoke statepoint.
     const SDValue Chain = DAG.getRoot(); // != Builder.getRoot()
 
     auto &MF = DAG.getMachineFunction();
     auto &MFI = MF.getFrameInfo();
     auto PtrInfo = MachinePointerInfo::getFixedStack(MF, Index);
     auto *LoadMMO = MF.getMachineMemOperand(PtrInfo, MachineMemOperand::MOLoad,
                                             MFI.getObjectSize(Index),
                                             MFI.getObjectAlign(Index));
 
     auto LoadVT = DAG.getTargetLoweringInfo().getValueType(DAG.getDataLayout(),
                                                            Relocate.getType());
 
-  SDValue SpillLoad = DAG.getLoad(LoadVT, getCurSDLoc(), Chain,
-                                  SpillSlot, LoadMMO);
+    SDValue SpillLoad =
+        DAG.getLoad(LoadVT, getCurSDLoc(), Chain, SpillSlot, LoadMMO);
     PendingLoads.push_back(SpillLoad.getValue(1));
 
     assert(SpillLoad.getNode());
     setValue(&Relocate, SpillLoad);
+    return;
+  }
+
+  SDValue SD = getValue(DerivedPtr);
+
+  if (SD.isUndef() && SD.getValueType().getSizeInBits() <= 64) {
+    // Lowering relocate(undef) as arbitrary constant. Current constant value
+    // is chosen such that it's unlikely to be a valid pointer.
+    setValue(&Relocate, DAG.getTargetConstant(0xFEFEFEFE, SDLoc(SD), MVT::i64));
+    return;
+  }
+
+  // We didn't need to spill these special cases (constants and allocas).
+  // See the handling in spillIncomingValueForStatepoint for detail.
+  assert(Record.type == RecordType::NoRelocate);
+  setValue(&Relocate, SD);
 }
 
 void SelectionDAGBuilder::LowerDeoptimizeCall(const CallInst *CI) {
   const auto &TLI = DAG.getTargetLoweringInfo();
   SDValue Callee = DAG.getExternalSymbol(TLI.getLibcallName(RTLIB::DEOPTIMIZE),
                                          TLI.getPointerTy(DAG.getDataLayout()));
 
   // We don't lower calls to __llvm_deoptimize as varargs, but as a regular

llvm/test/CodeGen/X86/statepoint-spill-lowering.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -verify-machineinstrs < %s | FileCheck %s
+
+; Check that we can handle gc.relocate in a separate block in spill mode.
+
+target triple = "x86_64-pc-linux-gnu"
+
+declare void @"some_call"(i8 addrspace(1)*)
+declare i32 @"personality_function"()
+
+; CHECK-LABEL: test_invoke:
+define i8 addrspace(1)* @test_invoke(i8 addrspace(1)* %a, i8 addrspace(1)* %b, i8 addrspace(1)* %c, i8 addrspace(1)* %d, i8 addrspace(1)* %e, i8 addrspace(1)* %f, i8 addrspace(1)* %g, i8 addrspace(1)* %h, i8 addrspace(1)* %j, i8 addrspace(1)* %k, i8 addrspace(1)* %l, i8 addrspace(1)* %m, i8 addrspace(1)* %n, i8 addrspace(1)* %o, i8 addrspace(1)* %p, i8 addrspace(1)* %q, i8 addrspace(1)* %r, i8 addrspace(1)* %s, i8 addrspace(1)* %t)
+gc "statepoint-example" personality i32 ()* @"personality_function" {
+entry:
+  %0 = invoke token (i64, i32, void (i8 addrspace(1)*)*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidp1i8f(i64 0, i32 0, void (i8 addrspace(1)*)* @some_call, i32 1, i32 0, i8 addrspace(1)* %t, i32 0, i32 0) ["gc-live" (i8 addrspace(1)* %t)]
+          to label %invoke_safepoint_normal_dest unwind label %exceptional_return
+
+invoke_safepoint_normal_dest:
+  %t.relocated = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %0, i32 0, i32 0)
+  ret i8 addrspace(1)* %t.relocated
+
+exceptional_return:
+  %landing_pad = landingpad token
+          cleanup
+  ret i8 addrspace(1)* null
+}
+
+; CHECK-LABEL: test_call:
+define i8 addrspace(1)* @test_call(i8 addrspace(1)* %a, i8 addrspace(1)* %b, i8 addrspace(1)* %c, i8 addrspace(1)* %d, i8 addrspace(1)* %e, i8 addrspace(1)* %f, i8 addrspace(1)* %g, i8 addrspace(1)* %h, i8 addrspace(1)* %j, i8 addrspace(1)* %k, i8 addrspace(1)* %l, i8 addrspace(1)* %m, i8 addrspace(1)* %n, i8 addrspace(1)* %o, i8 addrspace(1)* %p, i8 addrspace(1)* %q, i8 addrspace(1)* %r, i8 addrspace(1)* %s, i8 addrspace(1)* %t)
+gc "statepoint-example" personality i32 ()* @"personality_function" {
+entry:
+  %0 = call token (i64, i32, void (i8 addrspace(1)*)*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidp1i8f(i64 0, i32 0, void (i8 addrspace(1)*)* @some_call, i32 1, i32 0, i8 addrspace(1)* %t, i32 0, i32 0) ["gc-live" (i8 addrspace(1)* %t)]
+  br label %other_block
+
+other_block:
+  %t.relocated = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token %0, i32 0, i32 0)
+  ret i8 addrspace(1)* %t.relocated
+}
+declare token @llvm.experimental.gc.statepoint.p0f_isVoidp1i8f(i64, i32, void (i8 addrspace(1)*)*, i32, i32, ...)
+declare i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(token, i32, i32)