Transform (x&C)>V into (x&C)!=0 where possible

[oota-llvm.git] / lib / Transforms / InstCombine / InstCombineCompares.cpp

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 1b96c3cca4ee30142a8106e8f588de9676dea23a..13516d15c4d21e8e9a68830102b7cdc3c8c40e29 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1226,6 +1226,16 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
         ICI.setOperand(0, NewAnd);
         return &ICI;
       }
+
+      // Replace ((X & AndCST) > RHSV) with ((X & AndCST) != 0), if any
+      // bit set in (X & AndCST) will produce a result greater than RHSV.
+      if (ICI.getPredicate() == ICmpInst::ICMP_UGT) {
+        unsigned NTZ = AndCST->getValue().countTrailingZeros();
+        if ((NTZ < AndCST->getBitWidth()) &&
+            APInt::getOneBitSet(AndCST->getBitWidth(), NTZ).ugt(RHSV))
+          return new ICmpInst(ICmpInst::ICMP_NE, LHSI,
+                              Constant::getNullValue(RHS->getType()));
+      }
     }
 
     // Try to optimize things like "A[i]&42 == 0" to index computations.