move isOnlyReachableByFallthrough out of MachineBasicBlock into AsmPrinter,

and add a sparc implementation that knows about delay slots.  Patch by
Nathan Keynes!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96492 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 35 insertions, 0 deletions

diff --git a/lib/Target/Sparc/AsmPrinter/SparcAsmPrinter.cpp b/lib/Target/Sparc/AsmPrinter/SparcAsmPrinter.cpp
index 9a2ce6b..ecb8b00 100644
--- a/lib/Target/Sparc/AsmPrinter/SparcAsmPrinter.cpp
+++ b/lib/Target/Sparc/AsmPrinter/SparcAsmPrinter.cpp
@@ -56,6 +56,9 @@ namespace {
                              unsigned AsmVariant, const char *ExtraCode);
 
     bool printGetPCX(const MachineInstr *MI, unsigned OpNo);
+    
+    virtual bool isBlockOnlyReachableByFallthrough(const MachineBasicBlock *MBB)
+                       const;
   };
 } // end of anonymous namespace
 
@@ -197,6 +200,38 @@ bool SparcAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
   return false;
 }
 
+/// isBlockOnlyReachableByFallthough - Return true if the basic block has
+/// exactly one predecessor and the control transfer mechanism between
+/// the predecessor and this block is a fall-through.
+/// Override AsmPrinter implementation to handle delay slots
+bool SparcAsmPrinter::isBlockOnlyReachableByFallthrough(const MachineBasicBlock *MBB) 
+    const {
+  // If this is a landing pad, it isn't a fall through.  If it has no preds,
+  // then nothing falls through to it.
+  if (MBB->isLandingPad() || MBB->pred_empty())
+    return false;
+  
+  // If there isn't exactly one predecessor, it can't be a fall through.
+  MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(), PI2 = PI;
+  ++PI2;
+  if (PI2 != MBB->pred_end())
+    return false;
+  
+  // The predecessor has to be immediately before this block.
+  const MachineBasicBlock *Pred = *PI;
+  
+  if (!Pred->isLayoutSuccessor(MBB))
+    return false;
+  
+  // Check if the last terminator is an unconditional branch
+  MachineBasicBlock::const_iterator I = Pred->end();
+  while( I != Pred->begin() && !(--I)->getDesc().isTerminator() )
+      ; /* Noop */
+  return I == Pred->end() || !I->getDesc().isBarrier();
+}
+
+
+
 // Force static initialization.
 extern "C" void LLVMInitializeSparcAsmPrinter() { 
   RegisterAsmPrinter<SparcAsmPrinter> X(TheSparcTarget);