[CXX_FAST_TLS] Disable tail call when calling conventions are mismatched.

Since CXX_FAST_TLS has a bigger set of CSRs, we don't tail call when caller
and callee have mismatched calling conventions.

llvm-svn: 263856

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index e0e46d912b5..a5af0fcf62f 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -3767,6 +3767,13 @@ bool X86TargetLowering::IsEligibleForTailCallOptimization(
   if (IsCalleeWin64 != IsCallerWin64)
     return false;
 
+  // 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;
+
   if (DAG.getTarget().Options.GuaranteedTailCallOpt) {
     if (canGuaranteeTCO(CalleeCC) && CCMatch)
       return true;