From d4b0873c06de66a00e28850f31c227995ecb1592 Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Tue, 30 Nov 2010 23:55:39 +0000
Subject: 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
---
 llvm/lib/Target/X86/X86ISelLowering.cpp | 41 ++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 11 deletions(-)

(limited to 'llvm/lib/Target/X86/X86ISelLowering.cpp')

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(),
-- 
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