Enable sibling call optimization of libcalls which are expanded during

legalization time. Since at legalization time there is no mapping from
SDNode back to the corresponding LLVM instruction and the return
SDNode is target specific, this requires a target hook to check for
eligibility. Only x86 and ARM support this form of sibcall optimization
right now.
rdar://8707777

llvm-svn: 120501

1 files changed, 17 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 6f6dcc0b156..4b970e091fe 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -11,13 +11,14 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/CodeGen/SelectionDAG.h"
+#include "llvm/Analysis/DebugInfo.h"
+#include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineJumpTableInfo.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
-#include "llvm/Analysis/DebugInfo.h"
 #include "llvm/CodeGen/PseudoSourceValue.h"
+#include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/Target/TargetFrameInfo.h"
 #include "llvm/Target/TargetLowering.h"
 #include "llvm/Target/TargetData.h"
@@ -1948,12 +1949,20 @@ SDValue SelectionDAGLegalize::ExpandLibCall(RTLIB::Libcall LC, SDNode *Node,
 
   // Splice the libcall in wherever FindInputOutputChains tells us to.
   const Type *RetTy = Node->getValueType(0).getTypeForEVT(*DAG.getContext());
+
+  // isTailCall may be true since the callee does not reference caller stack
+  // frame. Check if it's in the right position.
+  bool isTailCall = isInTailCallPosition(DAG, Node, TLI);
   std::pair<SDValue, SDValue> CallInfo =
     TLI.LowerCallTo(InChain, RetTy, isSigned, !isSigned, false, false,
-                    0, TLI.getLibcallCallingConv(LC), false,
+                    0, TLI.getLibcallCallingConv(LC), isTailCall,
                     /*isReturnValueUsed=*/true,
                     Callee, Args, DAG, Node->getDebugLoc());
 
+  if (!CallInfo.second.getNode())
+    // It's a tailcall, return the chain (which is the DAG root).
+    return DAG.getRoot();
+
   // Legalize the call sequence, starting with the chain.  This will advance
   // the LastCALLSEQ_END to the legalized version of the CALLSEQ_END node that
   // was added by LowerCallTo (guaranteeing proper serialization of calls).
@@ -1988,7 +1997,7 @@ SelectionDAGLegalize::ExpandChainLibCall(RTLIB::Libcall LC,
   const Type *RetTy = Node->getValueType(0).getTypeForEVT(*DAG.getContext());
   std::pair<SDValue, SDValue> CallInfo =
     TLI.LowerCallTo(InChain, RetTy, isSigned, !isSigned, false, false,
-                    0, TLI.getLibcallCallingConv(LC), false,
+                    0, TLI.getLibcallCallingConv(LC), /*isTailCall=*/false,
                     /*isReturnValueUsed=*/true,
                     Callee, Args, DAG, Node->getDebugLoc());
 
@@ -2558,7 +2567,8 @@ void SelectionDAGLegalize::ExpandNode(SDNode *Node,
     TargetLowering::ArgListTy Args;
     std::pair<SDValue, SDValue> CallResult =
       TLI.LowerCallTo(Node->getOperand(0), Type::getVoidTy(*DAG.getContext()),
-                      false, false, false, false, 0, CallingConv::C, false,
+                      false, false, false, false, 0, CallingConv::C,
+                      /*isTailCall=*/false,
                       /*isReturnValueUsed=*/true,
                       DAG.getExternalSymbol("__sync_synchronize",
                                             TLI.getPointerTy()),
@@ -2609,7 +2619,8 @@ void SelectionDAGLegalize::ExpandNode(SDNode *Node,
     TargetLowering::ArgListTy Args;
     std::pair<SDValue, SDValue> CallResult =
       TLI.LowerCallTo(Node->getOperand(0), Type::getVoidTy(*DAG.getContext()),
-                      false, false, false, false, 0, CallingConv::C, false,
+                      false, false, false, false, 0, CallingConv::C,
+                      /*isTailCall=*/false,
                       /*isReturnValueUsed=*/true,
                       DAG.getExternalSymbol("abort", TLI.getPointerTy()),
                       Args, DAG, dl);