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)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185024 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 23 insertions, 4 deletions

diff --git a/lib/Target/ARM/ARMBaseRegisterInfo.cpp b/lib/Target/ARM/ARMBaseRegisterInfo.cpp
index 3ba3b625d7..0e1e50e529 100644
--- a/lib/Target/ARM/ARMBaseRegisterInfo.cpp
+++ b/lib/Target/ARM/ARMBaseRegisterInfo.cpp
@@ -75,6 +75,9 @@ const uint32_t*
 ARMBaseRegisterInfo::getThisReturnPreservedMask(CallingConv::ID) const {
   return (STI.isTargetIOS() && !STI.isAAPCS_ABI())
     ? CSR_iOS_ThisReturn_RegMask : CSR_AAPCS_ThisReturn_RegMask;
+  // This should return NULL in the case of any calling convention that does
+  // not use the same register for an i32 first argument and an i32 return
+  // value
 }
 
 const uint32_t*
diff --git a/lib/Target/ARM/ARMBaseRegisterInfo.h b/lib/Target/ARM/ARMBaseRegisterInfo.h
index 03b3682541..be3f1368f6 100644
--- a/lib/Target/ARM/ARMBaseRegisterInfo.h
+++ b/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*
diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 6b981d5ba5..c8d73d76d7 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -1711,10 +1711,17 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   const uint32_t *Mask;
   const TargetRegisterInfo *TRI = getTargetMachine().getRegisterInfo();
   const ARMBaseRegisterInfo *ARI = static_cast<const ARMBaseRegisterInfo*>(TRI);
-  if (isThisReturn)
-    // For 'this' returns, use the R0-preserving mask
+  if (isThisReturn) {
+    // For 'this' returns, use the R0-preserving mask if applicable
     Mask = ARI->getThisReturnPreservedMask(CallConv);
-  else
+    if (!Mask) {
+      // Set isThisReturn to false if the calling convention is not one that
+      // allows 'returned' to be modeled in this way, so LowerCallResult does
+      // not try to pass 'this' straight through 
+      isThisReturn = false;
+      Mask = ARI->getCallPreservedMask(CallConv);
+    }
+  } else
     Mask = ARI->getCallPreservedMask(CallConv);
 
   assert(Mask && "Missing call preserved mask for calling convention");