[GIsel][LegalizerHelper] Account for debug insts when creating mem libcalls

[vsk]

Summary

While lowering memory intrinsics, GIsel attempts to form a tail call to
a library routine.

There might be a DBG_LABEL or something after the intrinsic call,
though: in that case, GIsel should still be able to form the tail call,
and should also delete the debug insts after the tail call as the
transform makes them invalid.

[arsenm]

llvm/test/CodeGen/AArch64/GlobalISel/legalize-memcpy-et-al.mir

3

Does this end up stressing the case with multiple dbg instructions? I think tests with explicit dbg instructions would be more helpful here

[vsk]

Add explicit debug info test

[vsk]

llvm/test/CodeGen/AArch64/GlobalISel/legalize-memcpy-et-al.mir

3

This should be covered by the added test. PTAL, thanks.

[aemerson]

LGTM.

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

case TargetOpcode::G_FNEARBYINT:
     RTLIBCASE(NEARBYINT_F);
   }
   llvm_unreachable("Unknown libcall function");
 }
 
 /// True if an instruction is in tail position in its caller. Intended for
 /// legalizing libcalls as tail calls when possible.
 static bool isLibCallInTailPosition(MachineInstr &MI) {
-  const Function &F = MI.getParent()->getParent()->getFunction();
+  MachineBasicBlock &MBB = *MI.getParent();
+  const Function &F = MBB.getParent()->getFunction();
 
   // Conservatively require the attributes of the call to match those of
   // the return. Ignore NoAlias and NonNull because they don't affect the
   // call sequence.
   AttributeList CallerAttrs = F.getAttributes();
   if (AttrBuilder(CallerAttrs, AttributeList::ReturnIndex)
           .removeAttribute(Attribute::NoAlias)
           .removeAttribute(Attribute::NonNull)
           .hasAttributes())
     return false;
 
   // It's not safe to eliminate the sign / zero extension of the return value.
   if (CallerAttrs.hasAttribute(AttributeList::ReturnIndex, Attribute::ZExt) ||
       CallerAttrs.hasAttribute(AttributeList::ReturnIndex, Attribute::SExt))
     return false;
 
   // Only tail call if the following instruction is a standard return.
   auto &TII = *MI.getMF()->getSubtarget().getInstrInfo();
-  MachineInstr *Next = MI.getNextNode();
-  if (!Next || TII.isTailCall(*Next) || !Next->isReturn())
+  auto Next = next_nodbg(MI.getIterator(), MBB.instr_end());
+  if (Next == MBB.instr_end() || TII.isTailCall(*Next) || !Next->isReturn())
     return false;
 
   return true;
 }
 
 LegalizerHelper::LegalizeResult
 llvm::createLibcall(MachineIRBuilder &MIRBuilder, const char *Name,
                     const CallLowering::ArgInfo &Result,
Info.IsTailCall = MI.getOperand(MI.getNumOperands() - 1).getImm() == 1 &&
                     isLibCallInTailPosition(MI);
 
   std::copy(Args.begin(), Args.end(), std::back_inserter(Info.OrigArgs));
   if (!CLI.lowerCall(MIRBuilder, Info))
     return LegalizerHelper::UnableToLegalize;
 
   if (Info.LoweredTailCall) {
     assert(Info.IsTailCall && "Lowered tail call when it wasn't a tail call?");
-    // We must have a return following the call to get past
+    // We must have a return following the call (or debug insts) to get past
     // isLibCallInTailPosition.
-    assert(MI.getNextNode() && MI.getNextNode()->isReturn() &&
-           "Expected instr following MI to be a return?");
-
+    do {
+      MachineInstr *Next = MI.getNextNode();
+      assert(Next && (Next->isReturn() || Next->isDebugInstr()) &&
+             "Expected instr following MI to be return or debug inst?");
       // We lowered a tail call, so the call is now the return from the block.
       // Delete the old return.
-    MI.getNextNode()->eraseFromParent();
+      Next->eraseFromParent();
+    } while (MI.getNextNode());
   }
 
   return LegalizerHelper::Legalized;
 }
 
 static RTLIB::Libcall getConvRTLibDesc(unsigned Opcode, Type *ToType,
                                        Type *FromType) {
   auto ToMVT = MVT::getVT(ToType);

llvm/test/CodeGen/AArch64/GlobalISel/legalize-memcpy-et-al.mir

 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
 # RUN: llc -march=aarch64 -run-pass=legalizer -verify-machineinstrs %s -o - | FileCheck %s
+# RUN: llc -debugify-and-strip-all-safe -march=aarch64 -run-pass=legalizer -verify-machineinstrs %s -o - | FileCheck %s
 ---
 name:            test_memcpy
 tracksRegLiveness: true
 body:             |
   bb.1:
     liveins: $w2, $x0, $x1
 
     ; CHECK-LABEL: name: test_memcpy