[NVPTX] Lower instructions that expand into libcalls.

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.

With this patch LLVM produces a more sensible error message:
> Cannot select: ... i32 = ExternalSymbol'__foobar'

Author: Denys Zariaiev <denys.zariaiev@gmail.com>

Differential Revision: https://reviews.llvm.org/D55145

llvm-svn: 349213

llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp

@@ -1661,7 +1661,12 @@ SDValue NVPTXTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
     }
   }
 
-  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 _);
@@ -1685,7 +1690,7 @@ SDValue NVPTXTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
     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::PrintCall : NVPTXISD::PrintCallUni;
   if (CLI.IsConvergent)
     Opcode = Opcode == NVPTXISD::PrintCallUni ? NVPTXISD::PrintConvergentCallUni
                                               : NVPTXISD::PrintConvergentCall;
@@ -1719,12 +1724,12 @@ SDValue NVPTXTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   }
   SDVTList CallArgEndVTs = DAG.getVTList(MVT::Other, MVT::Glue);
   SDValue CallArgEndOps[] = { Chain,
-                              DAG.getConstant(Func ? 1 : 0, dl, MVT::i32),
+                              DAG.getConstant(isIndirectCall ? 0 : 1, 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),

llvm/test/CodeGen/NVPTX/libcall-instruction.ll

@@ -0,0 +1,8 @@
+; 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
+}