Move callseq_start above the call address load to allow load to be folded into the call node.

llvm-svn: 55292

2 files changed, 17 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 5d8cb1cd291..09a30db218a 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -1457,12 +1457,12 @@ EmitTailCallStoreRetAddr(SelectionDAG & DAG, MachineFunction &MF,
 
 SDValue X86TargetLowering::LowerCALL(SDValue Op, SelectionDAG &DAG) {
   MachineFunction &MF = DAG.getMachineFunction();
-  SDValue Chain     = Op.getOperand(0);
+  SDValue Chain       = Op.getOperand(0);
   unsigned CC         = cast<ConstantSDNode>(Op.getOperand(1))->getValue();
   bool isVarArg       = cast<ConstantSDNode>(Op.getOperand(2))->getValue() != 0;
   bool IsTailCall     = cast<ConstantSDNode>(Op.getOperand(3))->getValue() != 0
                         && CC == CallingConv::Fast && PerformTailCallOpt;
-  SDValue Callee    = Op.getOperand(4);
+  SDValue Callee      = Op.getOperand(4);
   bool Is64Bit        = Subtarget->is64Bit();
   bool IsStructRet    = CallIsStructReturn(Op);
 
@@ -1499,6 +1499,11 @@ SDValue X86TargetLowering::LowerCALL(SDValue Op, SelectionDAG &DAG) {
       MF.getInfo<X86MachineFunctionInfo>()->setTCReturnAddrDelta(FPDiff);
   }
 
+  // If the address is a load, i.e. indirect function call, move callseq_start
+  // above the load. This makes it possible for the load to fold into the call.
+  if (Callee.Val == Chain.Val && ISD::isNormalLoad(Callee.Val) &&
+      Chain.hasOneUse() && Callee.hasOneUse())
+    Chain = Chain.getOperand(0);
   Chain = DAG.getCALLSEQ_START(Chain, DAG.getIntPtrConstant(NumBytes));
 
   SDValue RetAddrFrIdx;
diff --git a/llvm/test/CodeGen/X86/fold-call-2.ll b/llvm/test/CodeGen/X86/fold-call-2.ll
new file mode 100644
index 00000000000..349f986830a
--- /dev/null
+++ b/llvm/test/CodeGen/X86/fold-call-2.ll
@@ -0,0 +1,10 @@
+; RUN: llvm-as < %s | llc -mtriple=i386-apple-darwin | grep mov | count 1
+
+@f = external global void ()*		; <void ()**> [#uses=1]
+
+define i32 @main() nounwind {
+entry:
+	load void ()** @f, align 8		; <void ()*>:0 [#uses=1]
+	tail call void %0( ) nounwind
+	ret i32 0
+}