From 32a5f02598a815b3add3a8e42fb58504201d0b5d Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Wed, 19 Jan 2005 17:29:49 +0000
Subject: [PATCH] Know some simple identities.  This improves codegen for (1LL
 << N).

llvm-svn: 19698
---
 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 3da2f5fe7ab3..3b106d192d13 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -615,6 +615,19 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
         std::swap(N1, N2);
       }
     }
+
+    switch (Opcode) {
+    default: break;
+    case ISD::SHL:    // shl  0, X -> 0
+      if (N1C->isNullValue()) return N1;
+      break;
+    case ISD::SRL:    // srl  0, X -> 0
+      if (N1C->isNullValue()) return N1;
+      break;
+    case ISD::SRA:    // sra -1, X -> -1
+      if (N1C->isAllOnesValue()) return N1;
+      break;
+    }
   }
 
   if (N2C) {