Handle constant addresses more efficiently, folding the low bits into the

disp field of the load/store if possible.  This compiles
CodeGen/PowerPC/load-constant-addr.ll to:

_test:
        lis r2, 2838
        lfs f1, 26848(r2)
        blr

instead of:

_test:
        lis r2, 2838
        ori r2, r2, 26848
        lfs f1, 0(r2)
        blr

llvm-svn: 26908

1 files changed, 17 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 61e279c046e..bc6573b13c5 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -535,7 +535,24 @@ bool PPCDAGToDAGISel::SelectAddrImm(SDOperand N, SDOperand &Disp,
         return true;
       }
     }
+  } else if (ConstantSDNode *CN = dyn_cast<ConstantSDNode>(N)) {
+    // Loading from a constant address.
+    int Addr = (int)CN->getValue();
+    
+    // If this address fits entirely in a 16-bit sext immediate field, codegen
+    // this as "d, 0"
+    if (Addr == (short)Addr) {
+      Disp = getI32Imm(Addr);
+      Base = CurDAG->getRegister(PPC::R0, MVT::i32);
+      return true;
+    }
+    
+    // Otherwise, break this down into an LIS + disp.
+    Disp = getI32Imm((short)Addr);
+    Base = CurDAG->getConstant(Addr - (signed short)Addr, MVT::i32);
+    return true;
   }
+  
   Disp = getI32Imm(0);
   if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(N))
     Base = CurDAG->getTargetFrameIndex(FI->getIndex(), MVT::i32);