For the current Atom processor, the fastest way to handle a call

indirect through a memory address is to load the memory address into
a register and then call indirect through the register.

This patch implements this improvement by modifying SelectionDAG to
force a function address which is a memory reference to be loaded
into a virtual register.

Patch by Sriram Murali.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178171 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 13 insertions, 0 deletions

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 9ef6a3bca0..0eaab0f818 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -2629,6 +2629,19 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
     InFlag = Chain.getValue(1);
   }
 
+  // Use indirect reference through register, when CALL uses a memory reference.
+  if (Subtarget->callRegIndirect() &&
+      Callee.getOpcode() == ISD::LOAD) {
+    const TargetRegisterClass *AddrRegClass =
+      getRegClassFor(Subtarget->is64Bit() ? MVT::i64:MVT::i32);
+    MachineRegisterInfo &MRI = MF.getRegInfo();
+    unsigned VReg = MRI.createVirtualRegister(AddrRegClass);
+    SDValue tempValue = DAG.getCopyFromReg(Callee,
+                                           dl, VReg, Callee.getValueType());
+    Chain = DAG.getCopyToReg(Chain, dl, VReg, tempValue, InFlag);
+    InFlag = Chain.getValue(1);
+  }
+
   Ops.push_back(Chain);
   Ops.push_back(Callee);