commit 88218ef706ba6fffc3b3f3c894910eea0f59abb1
author Chris Lattner <sabre@nondot.org> Wed Jan 19 17:29:49 2005 +0000
committer Chris Lattner <sabre@nondot.org> Wed Jan 19 17:29:49 2005 +0000
tree bc89d71f6389dbd9448a93dab8905d5fd02883b6
parent c3c021bcadd580a0764e12527f58a94389ae81ce

Know some simple identities.  This improves codegen for (1LL << N).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@19698 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 3da2f5f..3b106d1 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -615,6 +615,19 @@
         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) {