ARM, AArch64, X86: Check preserved registers for tail calls.

We can only perform a tail call to a callee that preserves all the
registers that the caller needs to preserve.

This situation happens with calling conventions like preserver_mostcc or
cxx_fast_tls. It was explicitely handled for fast_tls and failing for
preserve_most. This patch generalizes the check to any calling
convention.

Related to rdar://24207743

Differential Revision: http://reviews.llvm.org/D18680

llvm-svn: 265329

1 files changed, 7 insertions, 8 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 908f40db587..f950adb9159 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -2101,14 +2101,6 @@ ARMTargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
   MachineFunction &MF = DAG.getMachineFunction();
   const Function *CallerF = MF.getFunction();
   CallingConv::ID CallerCC = CallerF->getCallingConv();
-  bool CCMatch = CallerCC == CalleeCC;
-
-  // Disable tailcall for CXX_FAST_TLS when callee and caller have different
-  // calling conventions, given that CXX_FAST_TLS has a bigger CSR set.
-  if (!CCMatch &&
-      (CallerCC == CallingConv::CXX_FAST_TLS ||
-       CalleeCC == CallingConv::CXX_FAST_TLS))
-    return false;
 
   assert(Subtarget->supportsTailCall());
 
@@ -2152,6 +2144,13 @@ ARMTargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
                                   CCAssignFnForNode(CalleeCC, true, isVarArg),
                                   CCAssignFnForNode(CallerCC, true, isVarArg)))
     return false;
+  // The callee has to preserve all registers the caller needs to preserve.
+  if (CalleeCC != CallerCC) {
+    const ARMBaseRegisterInfo *TRI = Subtarget->getRegisterInfo();
+    if (!TRI->regmaskSubsetEqual(TRI->getCallPreservedMask(MF, CallerCC),
+                                 TRI->getCallPreservedMask(MF, CalleeCC)))
+      return false;
+  }
 
   // If Caller's vararg or byval argument has been split between registers and
   // stack, do not perform tail call, since part of the argument is in caller's