[SystemZ] Implement backchain attribute.

This introduces a SystemZ-specific "backchain" attribute on function, which
enables writing the frame backchain link as specified by the ABI.  This will
be used to implement -mbackchain option in clang.

Differential Revision: http://reviews.llvm.org/D19889

llvm-svn: 268571

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
index 0bdfaf67c40..866e0db7c90 100644
--- a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
@@ -354,6 +354,15 @@ void SystemZFrameLowering::emitPrologue(MachineFunction &MF,
 
   uint64_t StackSize = getAllocatedStackSize(MF);
   if (StackSize) {
+    // Determine if we want to store a backchain.
+    bool StoreBackchain = MF.getFunction()->hasFnAttribute("backchain");
+
+    // If we need backchain, save current stack pointer.  R1 is free at this
+    // point.
+    if (StoreBackchain)
+      BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::LGR))
+        .addReg(SystemZ::R1D).addReg(SystemZ::R15D);
+
     // Allocate StackSize bytes.
     int64_t Delta = -int64_t(StackSize);
     emitIncrement(MBB, MBBI, DL, SystemZ::R15D, Delta, ZII);
@@ -364,6 +373,10 @@ void SystemZFrameLowering::emitPrologue(MachineFunction &MF,
     BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
         .addCFIIndex(CFIIndex);
     SPOffsetFromCFA += Delta;
+
+    if (StoreBackchain)
+      BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::STG))
+        .addReg(SystemZ::R1D).addReg(SystemZ::R15D).addImm(0).addReg(0);
   }
 
   if (HasFP) {