Fix a long standing tail call optimization bug. When a libcall is emitted

legalizer always use the DAG entry node. This is wrong when the libcall is
emitted as a tail call since it effectively folds the return node. If
the return node's input chain is not the entry (i.e. call, load, or store)
use that as the tail call input chain.

PR12419
rdar://9770785
rdar://11195178

llvm-svn: 154370

2 files changed, 43 insertions, 34 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index e9b1c5f5008..fcb4f4fd097 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -1934,59 +1934,68 @@ ARMTargetLowering::LowerReturn(SDValue Chain,
   return result;
 }
 
-bool ARMTargetLowering::isUsedByReturnOnly(SDNode *N) const {
+bool ARMTargetLowering::isUsedByReturnOnly(SDNode *N, SDValue &Chain) const {
   if (N->getNumValues() != 1)
     return false;
   if (!N->hasNUsesOfValue(1, 0))
     return false;
 
-  unsigned NumCopies = 0;
-  SDNode* Copies[2] = { 0, 0 };
-  SDNode *Use = *N->use_begin();
-  if (Use->getOpcode() == ISD::CopyToReg) {
-    Copies[NumCopies++] = Use;
-  } else if (Use->getOpcode() == ARMISD::VMOVRRD) {
+  SDValue TCChain = Chain;
+  SDNode *Copy = *N->use_begin();
+  if (Copy->getOpcode() == ISD::CopyToReg) {
+    // If the copy has a glue operand, we conservatively assume it isn't safe to
+    // perform a tail call.
+    if (Copy->getOperand(Copy->getNumOperands()-1).getValueType() == MVT::Glue)
+      return false;
+    TCChain = Copy->getOperand(0);
+  } else if (Copy->getOpcode() == ARMISD::VMOVRRD) {
+    SDNode *VMov = Copy;
     // f64 returned in a pair of GPRs.
-    for (SDNode::use_iterator UI = Use->use_begin(), UE = Use->use_end();
+    SmallPtrSet<SDNode*, 2> Copies;
+    for (SDNode::use_iterator UI = VMov->use_begin(), UE = VMov->use_end();
          UI != UE; ++UI) {
       if (UI->getOpcode() != ISD::CopyToReg)
         return false;
-      Copies[UI.getUse().getResNo()] = *UI;
-      ++NumCopies;
+      Copies.insert(*UI);
+    }
+    if (Copies.size() > 2)
+      return false;
+
+    for (SDNode::use_iterator UI = VMov->use_begin(), UE = VMov->use_end();
+         UI != UE; ++UI) {
+      SDValue UseChain = UI->getOperand(0);
+      if (Copies.count(UseChain.getNode()))
+        // Second CopyToReg
+        Copy = *UI;
+      else
+        // First CopyToReg
+        TCChain = UseChain;
     }
-  } else if (Use->getOpcode() == ISD::BITCAST) {
+  } else if (Copy->getOpcode() == ISD::BITCAST) {
     // f32 returned in a single GPR.
-    if (!Use->hasNUsesOfValue(1, 0))
+    if (!Copy->hasOneUse())
       return false;
-    Use = *Use->use_begin();
-    if (Use->getOpcode() != ISD::CopyToReg || !Use->hasNUsesOfValue(1, 0))
+    Copy = *Copy->use_begin();
+    if (Copy->getOpcode() != ISD::CopyToReg || !Copy->hasNUsesOfValue(1, 0))
       return false;
-    Copies[NumCopies++] = Use;
+    Chain = Copy->getOperand(0);
   } else {
     return false;
   }
 
-  if (NumCopies != 1 && NumCopies != 2)
-    return false;
-
   bool HasRet = false;
-  for (unsigned i = 0; i < NumCopies; ++i) {
-    SDNode *Copy = Copies[i];
-    for (SDNode::use_iterator UI = Copy->use_begin(), UE = Copy->use_end();
-         UI != UE; ++UI) {
-      if (UI->getOpcode() == ISD::CopyToReg) {
-        SDNode *Use = *UI;
-        if (Use == Copies[0] || ((NumCopies == 2) && (Use == Copies[1])))
-          continue;
-        return false;
-      }
-      if (UI->getOpcode() != ARMISD::RET_FLAG)
-        return false;
-      HasRet = true;
-    }
+  for (SDNode::use_iterator UI = Copy->use_begin(), UE = Copy->use_end();
+       UI != UE; ++UI) {
+    if (UI->getOpcode() != ARMISD::RET_FLAG)
+      return false;
+    HasRet = true;
   }
 
-  return HasRet;
+  if (!HasRet)
+    return false;
+
+  Chain = TCChain;
+  return true;
 }
 
 bool ARMTargetLowering::mayBeEmittedAsTailCall(CallInst *CI) const {
diff --git a/llvm/lib/Target/ARM/ARMISelLowering.h b/llvm/lib/Target/ARM/ARMISelLowering.h
index 80c5716bb00..352d98001dd 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.h
+++ b/llvm/lib/Target/ARM/ARMISelLowering.h
@@ -493,7 +493,7 @@ namespace llvm {
                   const SmallVectorImpl<SDValue> &OutVals,
                   DebugLoc dl, SelectionDAG &DAG) const;
 
-    virtual bool isUsedByReturnOnly(SDNode *N) const;
+    virtual bool isUsedByReturnOnly(SDNode *N, SDValue &Chain) const;
 
     virtual bool mayBeEmittedAsTailCall(CallInst *CI) const;