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, 3 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 6b981d5ba52..c8d73d76d75 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/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");