Optimize sext/zext insertion algorithm in back-end.

With this optimization, we will not always insert zext for values crossing
basic blocks, but insert sext if the users of a value crossing basic block
has preference of sign predicate.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218101 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/FunctionLoweringInfo.h

@@ -21,6 +21,7 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/ISDOpcodes.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/Target/TargetRegisterInfo.h"
@@ -106,6 +107,10 @@ public:
                     KnownZero(1, 0) {}
   };
 
+  /// Record the preferred extend type (ISD::SIGN_EXTEND or ISD::ZERO_EXTEND)
+  /// for a value.
+  DenseMap<const Value *, ISD::NodeType> PreferredExtendType;
+
   /// VisitedBBs - The set of basic blocks visited thus far by instruction
   /// selection.
   SmallPtrSet<const BasicBlock*, 4> VisitedBBs;