ARM: Proactively ensure that the LowerCallResult hack for 'this'-returns is not used for incompatible calling conventions.

(Currently, ARM 'this'-returns are handled in the standard calling convention case by treating R0 as preserved and doing some extra magic in LowerCallResult; this may not apply to calling conventions added in the future so this patch provides and documents an interface for indicating such)

llvm-svn: 185024

1 files changed, 10 insertions, 1 deletions

diff --git a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.h b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.h
index 03b36825419..be3f1368f69 100644
--- a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.h
+++ b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.h
@@ -94,9 +94,18 @@ public:
   /// Code Generation virtual methods...
   const uint16_t *getCalleeSavedRegs(const MachineFunction *MF = 0) const;
   const uint32_t *getCallPreservedMask(CallingConv::ID) const;
-  const uint32_t *getThisReturnPreservedMask(CallingConv::ID) const;
   const uint32_t *getNoPreservedMask() const;
 
+  // getThisReturnPreservedMask - Returns a call preserved mask specific to the
+  // case that 'returned' is  an i32 first argument if the calling convention
+  // is one that can (partially) model this attribute with a preserved mask
+  // (i.e. it is a calling convention that uses the same register for the first
+  // i32 argument and an i32 return value)
+  //
+  // Should return NULL in the case that the calling convention does not have
+  // this property
+  const uint32_t *getThisReturnPreservedMask(CallingConv::ID) const;
+  
   BitVector getReservedRegs(const MachineFunction &MF) const;
 
   const TargetRegisterClass*