Reenable tail calls for iOS 5.0 and later.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141370 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/ARMISelLowering.cpp

@@ -1222,8 +1222,8 @@ ARMTargetLowering::LowerCall(SDValue Chain, SDValue Callee,
   MachineFunction &MF = DAG.getMachineFunction();
   bool IsStructRet    = (Outs.empty()) ? false : Outs[0].Flags.isSRet();
   bool IsSibCall = false;
-  // Temporarily disable tail calls so things don't break.
-  if (!EnableARMTailCalls)
+  // Disable tail calls if they're not supported.
+  if (!EnableARMTailCalls && !Subtarget->supportsTailCall())
     isTailCall = false;
   if (isTailCall) {
     // Check if it's really possible to do a tail call.

lib/Target/ARM/ARMSubtarget.cpp

@@ -60,6 +60,7 @@ ARMSubtarget::ARMSubtarget(const std::string &TT, const std::string &CPU,
   , PostRAScheduler(false)
   , IsR9Reserved(ReserveR9)
   , UseMovt(false)
+  , SupportsTailCall(false)
   , HasFP16(false)
   , HasD16(false)
   , HasHardwareDivide(false)
@@ -113,6 +114,8 @@ ARMSubtarget::ARMSubtarget(const std::string &TT, const std::string &CPU,
   else {
     IsR9Reserved = ReserveR9 | !HasV6Ops;
     UseMovt = DarwinUseMOVT && hasV6T2Ops();
+    const Triple &T = getTargetTriple();
+    SupportsTailCall = T.getOS() == Triple::IOS && !T.isOSVersionLT(5, 0);
   }
 
   if (!isThumb() || hasThumb2())

lib/Target/ARM/ARMSubtarget.h

@@ -93,6 +93,11 @@ protected:
   /// imms (including global addresses).
   bool UseMovt;
 
+  /// SupportsTailCall - True if the OS supports tail call. The dynamic linker
+  /// must be able to synthesize call stubs for interworking between ARM and
+  /// Thumb.
+  bool SupportsTailCall;
+
   /// HasFP16 - True if subtarget supports half-precision FP (We support VFP+HF
   /// only so far)
   bool HasFP16;
@@ -234,6 +239,7 @@ protected:
   bool isR9Reserved() const { return IsR9Reserved; }
 
   bool useMovt() const { return UseMovt && hasV6T2Ops(); }
+  bool supportsTailCall() const { return SupportsTailCall; }
 
   bool allowsUnalignedMem() const { return AllowsUnalignedMem; }
 

test/CodeGen/ARM/call-tc.ll

@@ -1,6 +1,10 @@
 ; RUN: llc < %s -mtriple=armv6-apple-darwin -mattr=+vfp2 -arm-tail-calls | FileCheck %s -check-prefix=CHECKV6
 ; RUN: llc < %s -mtriple=armv6-linux-gnueabi -relocation-model=pic -mattr=+vfp2 -arm-tail-calls | FileCheck %s -check-prefix=CHECKELF
 ; RUN: llc < %s -mtriple=thumbv7-apple-darwin -arm-tail-calls | FileCheck %s -check-prefix=CHECKT2D
+; RUN: llc < %s -mtriple=thumbv7-apple-ios5.0 | FileCheck %s -check-prefix=CHECKT2D
+
+; Enable tailcall optimization for iOS 5.0
+; rdar://9120031
 
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