[NVPTX] Lower instructions that expands into libcalls

[denzp]

Summary

The change is an effort to split and refactor abandoned D34708 into smaller parts.

Here the behaviour of unsupported instructions is changed to match the behaviour of explicit intrinsics calls. Currently LLVM crashes with:
Assertion getInstruction() && "Not a call or invoke instruction!" failed.

[tra]

Here the behaviour of unsupported instructions is changed to match the behaviour of explicit intrinsics calls.

If I remember correctly, the crash was only happening for instructions lowered to libcall. Do we crash in any other case?
If libcall is the only source of failure, would it make more sense to bail out of this function early? We're going to fail in this case anyways.

[denzp]

In D55145#1324230, @tra wrote:

Here the behaviour of unsupported instructions is changed to match the behaviour of explicit intrinsics calls.

If I remember correctly, the crash was only happening for instructions lowered to libcall. Do we crash in any other case?
If libcall is the only source of failure, would it make more sense to bail out of this function early? We're going to fail in this case anyways.

You are right, normally it would make sense. But in this case, the end goal is to support these libcalls.
It would be easier to achieve when both instructions and intrinsics are behaving consistently. And I'm afraid, bailing them out, would be an extra work that will have to be dropped when the final libcall solution will come (means, very-very soon).

[tra]

In D55145#1331301, @denzp wrote:

In D55145#1324230, @tra wrote:

Here the behaviour of unsupported instructions is changed to match the behaviour of explicit intrinsics calls.

If I remember correctly, the crash was only happening for instructions lowered to libcall. Do we crash in any other case?
If libcall is the only source of failure, would it make more sense to bail out of this function early? We're going to fail in this case anyways.

You are right, normally it would make sense. But in this case, the end goal is to support these libcalls.
It would be easier to achieve when both instructions and intrinsics are behaving consistently. And I'm afraid, bailing them out, would be an extra work that will have to be dropped when the final libcall solution will come (means, very-very soon).

OK.

The patch looks good to me.
One nit: I would suggest changing couple of conditional expressions that depend on !IsIndirectCall to use it without negation. It's a bit easier to read and understand.

lib/Target/NVPTX/NVPTXISelLowering.cpp

1681

-> = isIndirectCall ? NVPTXISD::PrintCall : NVPTXISD::PrintCallUni;

1715

!isIndirectCall ? 1 : 0 -> isIndirectCall ? 0 : 1

[denzp]

Done, thanks for the suggestion! Could you please commit it?

lib/Target/NVPTX/NVPTXISelLowering.cpp

if (RetTy->isFloatingPointTy() || RetTy->isPointerTy() ||
                                   DAG.getConstant(resultsz / 8, dl, MVT::i32),
                                   DAG.getConstant(0, dl, MVT::i32), InFlag };
       Chain = DAG.getNode(NVPTXISD::DeclareRetParam, dl, DeclareRetVTs,
                           DeclareRetOps);
       InFlag = Chain.getValue(1);
     }
   }
 
-  if (!Func) {
+  // Both indirect calls and libcalls have nullptr Func. In order to distinguish
+  // between them we must rely on the call site value which is valid for
+  // indirect calls but is always null for libcalls.
+  bool isIndirectCall = !Func && CS;
+
+  if (isIndirectCall) {
     // This is indirect function call case : PTX requires a prototype of the
     // form
     // proto_0 : .callprototype(.param .b32 _) _ (.param .b32 _);
     // to be emitted, and the label has to used as the last arg of call
     // instruction.
     // The prototype is embedded in a string and put as the operand for a
     // CallPrototype SDNode which will print out to the value of the string.
     SDVTList ProtoVTs = DAG.getVTList(MVT::Other, MVT::Glue);
     std::string Proto = getPrototype(DL, RetTy, Args, Outs, retAlignment, CS);
     const char *ProtoStr =
       nvTM->getManagedStrPool()->getManagedString(Proto.c_str())->c_str();
     SDValue ProtoOps[] = {
       Chain, DAG.getTargetExternalSymbol(ProtoStr, MVT::i32), InFlag,
     };
     Chain = DAG.getNode(NVPTXISD::CallPrototype, dl, ProtoVTs, ProtoOps);
     InFlag = Chain.getValue(1);
   }
   // Op to just print "call"
   SDVTList PrintCallVTs = DAG.getVTList(MVT::Other, MVT::Glue);
   SDValue PrintCallOps[] = {
     Chain, DAG.getConstant((Ins.size() == 0) ? 0 : 1, dl, MVT::i32), InFlag
   };
   // We model convergent calls as separate opcodes.
-  unsigned Opcode = Func ? NVPTXISD::PrintCallUni : NVPTXISD::PrintCall;
+  unsigned Opcode = !isIndirectCall ? NVPTXISD::PrintCallUni : NVPTXISD::PrintCall;
   if (CLI.IsConvergent)
     Opcode = Opcode == NVPTXISD::PrintCallUni ? NVPTXISD::PrintConvergentCallUni
                                               : NVPTXISD::PrintConvergentCall;
   Chain = DAG.getNode(Opcode, dl, PrintCallVTs, PrintCallOps);
   InFlag = Chain.getValue(1);
 
   // Ops to print out the function name
   SDVTList CallVoidVTs = DAG.getVTList(MVT::Other, MVT::Glue);
for (unsigned i = 0, e = paramCount; i != e; ++i) {
     SDVTList CallArgVTs = DAG.getVTList(MVT::Other, MVT::Glue);
     SDValue CallArgOps[] = { Chain, DAG.getConstant(1, dl, MVT::i32),
                              DAG.getConstant(i, dl, MVT::i32), InFlag };
     Chain = DAG.getNode(opcode, dl, CallArgVTs, CallArgOps);
     InFlag = Chain.getValue(1);
   }
   SDVTList CallArgEndVTs = DAG.getVTList(MVT::Other, MVT::Glue);
   SDValue CallArgEndOps[] = { Chain,
-                              DAG.getConstant(Func ? 1 : 0, dl, MVT::i32),
+                              DAG.getConstant(!isIndirectCall ? 1 : 0, dl, MVT::i32),
                               InFlag };
   Chain = DAG.getNode(NVPTXISD::CallArgEnd, dl, CallArgEndVTs, CallArgEndOps);
   InFlag = Chain.getValue(1);
 
-  if (!Func) {
+  if (isIndirectCall) {
     SDVTList PrototypeVTs = DAG.getVTList(MVT::Other, MVT::Glue);
     SDValue PrototypeOps[] = { Chain,
                                DAG.getConstant(uniqueCallSite, dl, MVT::i32),
                                InFlag };
     Chain = DAG.getNode(NVPTXISD::Prototype, dl, PrototypeVTs, PrototypeOps);
     InFlag = Chain.getValue(1);
   }
 

test/CodeGen/NVPTX/libcall-instruction.ll

+; RUN: not llc < %s -march=nvptx 2>&1 | FileCheck %s
+; used to panic on failed assetion and now fails with a "Cannot select"
+
+; CHECK: LLVM ERROR: Cannot select: {{t28|0x[0-9a-f]+}}: i32 = ExternalSymbol'__umodti3'
+define hidden i128 @remainder(i128, i128) {
+  %3 = urem i128 %0, %1
+  ret i128 %3
+}