From: Chris Lattner <sabre@nondot.org>
Date: Mon, 20 Mar 2006 22:38:22 +0000 (+0000)
Subject: Handle constant addresses more efficiently, folding the low bits into the
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=d97964457e972cc0c0ae0e293f975112c3d65c46;p=oota-llvm.git

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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26908 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 61e279c046e..bc6573b13c5 100644
--- a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/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);