Add a LiveRangeQuery class.

This class is meant to be the primary interface for examining a live
range in the vicinity on a given instruction. It avoids all the messy
dealings with iterators and early clobbers.

This is a more abstract interface to live ranges, hiding the
implementation as a vector of segments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157141 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveInterval.h

@@ -500,6 +500,91 @@ namespace llvm {
     return OS;
   }
 
+  /// LiveRangeQuery - Query information about a live range around a given
+  /// instruction. This class hides the implementation details of live ranges,
+  /// and it should be used as the primary interface for examining live ranges
+  /// around instructions.
+  ///
+  class LiveRangeQuery {
+    VNInfo *EarlyVal;
+    VNInfo *LateVal;
+    SlotIndex EndPoint;
+    bool Kill;
+
+  public:
+    /// Create a LiveRangeQuery for the given live range and instruction index.
+    /// The sub-instruction slot of Idx doesn't matter, only the instruction it
+    /// refers to is considered.
+    LiveRangeQuery(const LiveInterval &LI, SlotIndex Idx)
+      : EarlyVal(0), LateVal(0), Kill(false) {
+      // Find the segment that enters the instruction.
+      LiveInterval::const_iterator I = LI.find(Idx.getBaseIndex());
+      LiveInterval::const_iterator E = LI.end();
+      if (I == E)
+        return;
+      // Is this an instruction live-in segment?
+      if (SlotIndex::isEarlierInstr(I->start, Idx)) {
+        EarlyVal = I->valno;
+        EndPoint = I->end;
+        // Move to the potentially live-out segment.
+        if (SlotIndex::isSameInstr(Idx, I->end)) {
+          Kill = true;
+          if (++I == E)
+            return;
+        }
+      }
+      // I now points to the segment that may be live-through, or defined by
+      // this instr. Ignore segments starting after the current instr.
+      if (SlotIndex::isEarlierInstr(Idx, I->start))
+        return;
+      LateVal = I->valno;
+      EndPoint = I->end;
+    }
+
+    /// Return the value that is live-in to the instruction. This is the value
+    /// that will be read by the instruction's use operands. Return NULL if no
+    /// value is live-in.
+    VNInfo *valueIn() const {
+      return EarlyVal;
+    }
+
+    /// Return true if the live-in value is killed by this instruction. This
+    /// means that either the live range ends at the instruction, or it changes
+    /// value.
+    bool isKill() const {
+      return Kill;
+    }
+
+    /// Return true if this instruction has a dead def.
+    bool isDeadDef() const {
+      return EndPoint.isDead();
+    }
+
+    /// Return the value leaving the instruction, if any. This can be a
+    /// live-through value, or a live def. A dead def returns NULL.
+    VNInfo *valueOut() const {
+      return isDeadDef() ? 0 : LateVal;
+    }
+
+    /// Return the value defined by this instruction, if any. This includes
+    /// dead defs, it is the value created by the instruction's def operands.
+    VNInfo *valueDefined() const {
+      return EarlyVal == LateVal ? 0 : LateVal;
+    }
+
+    /// Return the end point of the last live range segment to interact with
+    /// the instruction, if any.
+    ///
+    /// The end point is an invalid SlotIndex only if the live range doesn't
+    /// intersect the instruction at all.
+    ///
+    /// The end point may be at or past the end of the instruction's basic
+    /// block. That means the value was live out of the block.
+    SlotIndex endPoint() const {
+      return EndPoint;
+    }
+  };
+
   /// ConnectedVNInfoEqClasses - Helper class that can divide VNInfos in a
   /// LiveInterval into equivalence clases of connected components. A
   /// LiveInterval that has multiple connected components can be broken into