[IPRA] Set callee saved registers to none for local function when IPRA is enabled.

IPRA try to optimize caller saved register by propagating register
usage information from callee to caller so it is beneficial to have
caller saved registers compare to callee saved registers when IPRA
is enabled. Please find more detailed explanation here
https://groups.google.com/d/msg/llvm-dev/XRzGhJ9wtZg/tjAJqb0eEgAJ.

This change makes local function do not have any callee preserved
register when IPRA is enabled. A simple test case is also added to
verify this change.

Patch by Vivek Pandya <vivekvpandya@gmail.com>

Differential Revision: http://reviews.llvm.org/D21561

llvm-svn: 275347

1 files changed, 10 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp b/llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp
index 0a0e0795c66..bb99166edd7 100644
--- a/llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp
+++ b/llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp
@@ -12,13 +12,14 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/BitVector.h"
-#include "llvm/Target/TargetFrameLowering.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
 #include "llvm/IR/CallingConv.h"
 #include "llvm/IR/Function.h"
+#include "llvm/Target/TargetFrameLowering.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 #include <cstdlib>
@@ -59,15 +60,21 @@ bool TargetFrameLowering::needsFrameIndexResolution(
 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
                                                BitVector &SavedRegs,
                                                RegScavenger *RS) const {
-  // Get the callee saved register list...
   const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
-  const MCPhysReg *CSRegs = TRI.getCalleeSavedRegs(&MF);
 
   // Resize before the early returns. Some backends expect that
   // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
   // saved registers.
   SavedRegs.resize(TRI.getNumRegs());
 
+  // When interprocedural register allocation is enabled caller saved registers
+  // are preferred over callee saved registers.
+  if (UseIPRA && isSafeForNoCSROpt(MF.getFunction()))
+    return;
+
+  // Get the callee saved register list...
+  const MCPhysReg *CSRegs = TRI.getCalleeSavedRegs(&MF);
+
   // Early exit if there are no callee saved registers.
   if (!CSRegs || CSRegs[0] == 0)
     return;