[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

1 files changed, 9 insertions, 4 deletions

diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
index eceb4fc6d88..5c16c34e21d 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
+++ b/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),