[AArch64] Break the dependency between FP and SP when possible.

When the SP in not changed because of realignment/VLAs etc., we restore the SP
by using the previous value of SP and not the FP. Breaking the dependency will
help in cases when the epilog of a callee is close to the epilog of the caller;
for then "sub sp, fp, #" depends on the load restoring the FP in the epilog of
the callee.

http://reviews.llvm.org/D18060
Patch by Aditya Kumar and Evandro Menezes.

llvm-svn: 263458

1 files changed, 9 insertions, 2 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.h b/llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.h
index 76ad2d12f0a..ebb05d5d258 100644
--- a/llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.h
+++ b/llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.h
@@ -79,18 +79,22 @@ class AArch64FunctionInfo : public MachineFunctionInfo {
   /// copies.
   bool IsSplitCSR;
 
+  /// True when the stack gets realigned dynamically because the size of stack
+  /// frame is unknown at compile time. e.g., in case of VLAs.
+  bool StackRealigned;
+
 public:
   AArch64FunctionInfo()
       : BytesInStackArgArea(0), ArgumentStackToRestore(0), HasStackFrame(false),
         NumLocalDynamicTLSAccesses(0), VarArgsStackIndex(0), VarArgsGPRIndex(0),
         VarArgsGPRSize(0), VarArgsFPRIndex(0), VarArgsFPRSize(0),
-        IsSplitCSR(false) {}
+        IsSplitCSR(false), StackRealigned(false) {}
 
   explicit AArch64FunctionInfo(MachineFunction &MF)
       : BytesInStackArgArea(0), ArgumentStackToRestore(0), HasStackFrame(false),
         NumLocalDynamicTLSAccesses(0), VarArgsStackIndex(0), VarArgsGPRIndex(0),
         VarArgsGPRSize(0), VarArgsFPRIndex(0), VarArgsFPRSize(0),
-        IsSplitCSR(false) {
+        IsSplitCSR(false), StackRealigned(false) {
     (void)MF;
   }
 
@@ -105,6 +109,9 @@ public:
   bool hasStackFrame() const { return HasStackFrame; }
   void setHasStackFrame(bool s) { HasStackFrame = s; }
 
+  bool isStackRealigned() const { return StackRealigned; }
+  void setStackRealigned(bool s) { StackRealigned = s; }
+
   bool isSplitCSR() const { return IsSplitCSR; }
   void setIsSplitCSR(bool s) { IsSplitCSR = s; }