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, 30 insertions, 11 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 6d6d83d5578..bc6d84eeec1 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -1338,6 +1338,23 @@ X86TargetLowering::LowerReturn(SDValue Chain,
                      MVT::Other, &RetOps[0], RetOps.size());
 }
 
+bool X86TargetLowering::isUsedByReturnOnly(SDNode *N) const {
+  if (N->getNumValues() != 1)
+    return false;
+  if (!N->hasNUsesOfValue(1, 0))
+    return false;
+
+  SDNode *Copy = *N->use_begin();
+  if (Copy->getOpcode() != ISD::CopyToReg)
+    return false;
+  for (SDNode::use_iterator UI = Copy->use_begin(), UE = Copy->use_end();
+       UI != UE; ++UI)
+    if (UI->getOpcode() != X86ISD::RET_FLAG)
+      return false;
+
+  return true;
+}
+
 /// LowerCallResult - Lower the result values of a call into the
 /// appropriate copies out of appropriate physical registers.
 ///
@@ -2142,17 +2159,19 @@ X86TargetLowering::LowerCall(SDValue Chain, SDValue Callee,
   } else if (ExternalSymbolSDNode *S = dyn_cast<ExternalSymbolSDNode>(Callee)) {
     unsigned char OpFlags = 0;
 
-    // On ELF targets, in either X86-64 or X86-32 mode, direct calls to external
-    // symbols should go through the PLT.
-    if (Subtarget->isTargetELF() &&
-        getTargetMachine().getRelocationModel() == Reloc::PIC_) {
-      OpFlags = X86II::MO_PLT;
-    } else if (Subtarget->isPICStyleStubAny() &&
-               Subtarget->getDarwinVers() < 9) {
-      // PC-relative references to external symbols should go through $stub,
-      // unless we're building with the leopard linker or later, which
-      // automatically synthesizes these stubs.
-      OpFlags = X86II::MO_DARWIN_STUB;
+    if (!isTailCall) {
+      // On ELF targets, in either X86-64 or X86-32 mode, direct calls to
+      // external symbols should go through the PLT.
+      if (Subtarget->isTargetELF() &&
+          getTargetMachine().getRelocationModel() == Reloc::PIC_) {
+        OpFlags = X86II::MO_PLT;
+      } else if (Subtarget->isPICStyleStubAny() &&
+                 Subtarget->getDarwinVers() < 9) {
+        // PC-relative references to external symbols should go through $stub,
+        // unless we're building with the leopard linker or later, which
+        // automatically synthesizes these stubs.
+        OpFlags = X86II::MO_DARWIN_STUB;
+      }
     }
 
     Callee = DAG.getTargetExternalSymbol(S->getSymbol(), getPointerTy(),