move ComputeMaskedBits, MaskedValueIsZero, and ComputeNumSignBits

out of instcombine into a new file in libanalysis.  This also teaches
ComputeNumSignBits about the number of sign bits in a constantint.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51863 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/ValueTracking.h

@@ -0,0 +1,48 @@
+//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains routines that help analyze properties that chains of
+// computations have.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_VALUETRACKING_H
+#define LLVM_ANALYSIS_VALUETRACKING_H
+
+namespace llvm {
+  class Value;
+  class APInt;
+  class TargetData;
+  
+  /// ComputeMaskedBits - Determine which of the bits specified in Mask are
+  /// known to be either zero or one and return them in the KnownZero/KnownOne
+  /// bit sets.  This code only analyzes bits in Mask, in order to short-circuit
+  /// processing.
+  void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
+                         APInt &KnownOne, TargetData *TD = 0,
+                         unsigned Depth = 0);
+  
+  bool MaskedValueIsZero(Value *V, const APInt &Mask, 
+                         TargetData *TD = 0, unsigned Depth = 0);
+
+  
+  /// ComputeNumSignBits - Return the number of times the sign bit of the
+  /// register is replicated into the other bits.  We know that at least 1 bit
+  /// is always equal to the sign bit (itself), but other cases can give us
+  /// information.  For example, immediately after an "ashr X, 2", we know that
+  /// the top 3 bits are all equal to each other, so we return 3.
+  ///
+  /// 'Op' must have a scalar integer type.
+  ///
+  unsigned ComputeNumSignBits(Value *Op, TargetData *TD = 0,
+                              unsigned Depth = 0);
+
+} // end namespace llvm
+
+#endif