[ValueTracking] Improve isImpliedCondition for conditions with matching operands.

This patch improves SimplifyCFG to catch cases like:

  if (a < b) {
    if (a > b) <- known to be false
      unreachable;
  }

Phabricator Revision: http://reviews.llvm.org/D18905

llvm-svn: 266767

1 files changed, 8 insertions, 6 deletions

diff --git a/llvm/include/llvm/Analysis/ValueTracking.h b/llvm/include/llvm/Analysis/ValueTracking.h
index 2486f2fdd8d..59e503c6040 100644
--- a/llvm/include/llvm/Analysis/ValueTracking.h
+++ b/llvm/include/llvm/Analysis/ValueTracking.h
@@ -436,16 +436,18 @@ template <typename T> class ArrayRef;
   /// E.g. if RangeMD is !{i32 0, i32 10, i32 15, i32 20} then return [0, 20).
   ConstantRange getConstantRangeFromMetadata(MDNode &RangeMD);
 
-  /// Return true if RHS is known to be implied by LHS.  A & B must be i1
-  /// (boolean) values or a vector of such values. Note that the truth table for
-  /// implication is the same as <=u on i1 values (but not <=s!).  The truth
-  /// table for both is:
+  /// Return true if RHS is known to be implied by LHS.  The implication may be
+  /// either true or false depending on what is returned in ImpliedTrue.
+  /// A & B must be i1 (boolean) values or a vector of such values. Note that
+  /// the truth table for implication is the same as <=u on i1 values (but not
+  /// <=s!).  The truth table for both is:
   ///    | T | F (B)
   ///  T | T | F
   ///  F | T | T
   /// (A)
-  bool isImpliedCondition(Value *LHS, Value *RHS, const DataLayout &DL,
-                          unsigned Depth = 0, AssumptionCache *AC = nullptr,
+  bool isImpliedCondition(Value *LHS, Value *RHS, bool &ImpliedTrue,
+                          const DataLayout &DL, unsigned Depth = 0,
+                          AssumptionCache *AC = nullptr,
                           const Instruction *CxtI = nullptr,
                           const DominatorTree *DT = nullptr);
 } // end namespace llvm