From 5c7656fd537bd8929e1569f0e319b5be560f2b90 Mon Sep 17 00:00:00 2001
From: Nate Begeman <natebegeman@mac.com>
Date: Thu, 11 Aug 2005 02:18:13 +0000
Subject: Add a select_cc optimization for recognizing abs(int).  This speeds
 up an integer MPEG encoding loop by a factor of two.

llvm-svn: 22758
---
 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

(limited to 'llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp')

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index e331c4a60bd..12482efd708 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1495,6 +1495,22 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
         return getNode(ISD::AND, AType, Shift, N3);
       }
     }
+    
+    // Check to see if this is an integer abs. select_cc setl[te] X, 0, -X, X ->
+    // Y = sra (X, size(X)-1); xor (add (X, Y), Y)
+    if (N2C && N2C->isNullValue() && (CC == ISD::SETLT || CC == ISD::SETLE) &&
+        N1 == N4 && N3.getOpcode() == ISD::SUB && N1 == N3.getOperand(1)) {
+      if (ConstantSDNode *SubC = dyn_cast<ConstantSDNode>(N3.getOperand(0))) {
+        MVT::ValueType XType = N1.getValueType();
+        if (SubC->isNullValue() && MVT::isInteger(XType)) {
+          SDOperand Shift = getNode(ISD::SRA, XType, N1,
+                                    getConstant(MVT::getSizeInBits(XType)-1,
+                                                TLI.getShiftAmountTy()));
+          return getNode(ISD::XOR, XType, getNode(ISD::ADD, XType, N1, Shift), 
+                         Shift);
+        }
+      }
+    }
   }
         
   std::vector<SDOperand> Ops;
-- 
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