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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@55292 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 5d8cb1cd291af23fc80696a5702845f5f34e118f..09a30db218a146b8746e774c5902ab13d585e60e 100644 (file)
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/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/test/CodeGen/X86/fold-call-2.ll b/test/CodeGen/X86/fold-call-2.ll
new file mode 100644 (file)
index 0000000..349f986
--- /dev/null
+++ b/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
+}