[NVPTX] Allow libcalls that are defined in the current module.

The patch adds a possibility to make library calls on NVPTX.

An important thing about library functions - they must be defined within
the current module. This basically should guarantee that we produce a
valid PTX assembly (without calls to not defined functions). The one who
wants to use the libcalls is probably will have to link against
compiler-rt or any other implementation.

Currently, it's completely impossible to make library calls because of
error LLVM ERROR: Cannot select: i32 = ExternalSymbol '...'. But we can
lower ExternalSymbol to TargetExternalSymbol and verify if the function
definition is available.

Also, there was an issue with a DAG during legalisation. When we expand
instruction into libcall, the inner call-chain isn't being "integrated"
into outer chain. Since the last "data-flow" (call retval load) node is
located in call-chain earlier than CALLSEQ_END node, the latter becomes
a leaf and therefore a dead node (and is being removed quite fast).
Proposed here solution relies on another data-flow pseudo nodes
(ProxyReg) which purpose is only to keep CALLSEQ_END at legalisation and
instruction selection phases - we remove the pseudo instructions before
register scheduling phase.

Patch by Denys Zariaiev!

Differential Revision: https://reviews.llvm.org/D34708

llvm-svn: 350069

1 files changed, 26 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index f38770b773f..3ae7bd90554 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -8464,6 +8464,32 @@ SDValue SelectionDAG::makeEquivalentMemoryOrdering(LoadSDNode *OldLoad,
   return TokenFactor;
 }
 
+SDValue SelectionDAG::getSymbolFunctionGlobalAddress(SDValue Op,
+                                                     Function **OutFunction) {
+  assert(isa<ExternalSymbolSDNode>(Op) && "Node should be an ExternalSymbol");
+
+  auto *Symbol = cast<ExternalSymbolSDNode>(Op)->getSymbol();
+  auto *Module = MF->getFunction().getParent();
+  auto *Function = Module->getFunction(Symbol);
+
+  if (OutFunction != nullptr)
+      *OutFunction = Function;
+
+  if (Function != nullptr) {
+    auto PtrTy = TLI->getPointerTy(getDataLayout(), Function->getAddressSpace());
+    return getGlobalAddress(Function, SDLoc(Op), PtrTy);
+  }
+
+  std::string ErrorStr;
+  raw_string_ostream ErrorFormatter(ErrorStr);
+
+  ErrorFormatter << "Undefined external symbol ";
+  ErrorFormatter << '"' << Symbol << '"';
+  ErrorFormatter.flush();
+
+  report_fatal_error(ErrorStr);
+}
+
 //===----------------------------------------------------------------------===//
 //                              SDNode Class
 //===----------------------------------------------------------------------===//