Re-apply r214881: Fix return sequence on armv4 thumb

This reverts r214893, re-applying r214881 with the test case relaxed a bit to
satiate the build bots.

POP on armv4t cannot be used to change thumb state (unilke later non-m-class
architectures), therefore we need a different return sequence that uses 'bx'
instead:

  POP {r3}
  ADD sp, #offset
  BX r3

This patch also fixes an issue where the return value in r3 would get clobbered
for functions that return 128 bits of data. In that case, we generate this
sequence instead:

  MOV ip, r3
  POP {r3}
  ADD sp, #offset
  MOV lr, r3
  MOV r3, ip
  BX lr

http://reviews.llvm.org/D4748

llvm-svn: 214928

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 8c4900b5b48..3e53af42b89 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -2113,6 +2113,10 @@ ARMTargetLowering::LowerReturn(SDValue Chain,
   RetOps.push_back(Chain); // Operand #0 = Chain (updated below)
   bool isLittleEndian = Subtarget->isLittle();
 
+  MachineFunction &MF = DAG.getMachineFunction();
+  ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
+  AFI->setReturnRegsCount(RVLocs.size());
+
   // Copy the result values into the output registers.
   for (unsigned i = 0, realRVLocIdx = 0;
        i != RVLocs.size();