InstCombine: If we have a bit test and a sign test anded/ored together, merge the sign bit into the bit test.

This is common in bit field code, e.g. checking if the first or the last bit of a bit field is set.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147749 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 32 insertions, 0 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 4b1e7feef0..96ca40a3cf 100644
--- a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -743,6 +743,22 @@ Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
       }
     }
   }
+
+  // (X & C) == 0 & X > -1  ->  (X & (C | SignBit)) == 0
+  if (LHS->hasOneUse() && RHS->hasOneUse() &&
+      ((LHSCC == ICmpInst::ICMP_EQ && LHSCst->isZero() &&
+        RHSCC == ICmpInst::ICMP_SGT && RHSCst->isAllOnesValue()) ||
+       (RHSCC == ICmpInst::ICMP_EQ && RHSCst->isZero() &&
+        LHSCC == ICmpInst::ICMP_SGT && LHSCst->isAllOnesValue()))) {
+    BinaryOperator *BO =
+      dyn_cast<BinaryOperator>(LHSCC == ICmpInst::ICMP_EQ ? Val : Val2);
+    ConstantInt *AndCst;
+    if (BO && match(BO, m_OneUse(m_And(m_Value(), m_ConstantInt(AndCst))))) {
+      APInt New = AndCst->getValue() | APInt::getSignBit(AndCst->getBitWidth());
+      BO->setOperand(1, ConstantInt::get(AndCst->getContext(), New));
+      return BO == Val ? LHS : RHS;
+    }
+  }
   
   // From here on, we only handle:
   //    (icmp1 A, C1) & (icmp2 A, C2) --> something simpler.
@@ -1442,6 +1458,22 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
     }
   }
 
+  // (X & C) != 0 & X < 0  ->  (X & (C | SignBit)) != 0
+  if (LHS->hasOneUse() && RHS->hasOneUse() &&
+      ((LHSCC == ICmpInst::ICMP_NE && LHSCst->isZero() &&
+        RHSCC == ICmpInst::ICMP_SLT && RHSCst->isZero()) ||
+       (RHSCC == ICmpInst::ICMP_NE && RHSCst->isZero() &&
+        LHSCC == ICmpInst::ICMP_SLT && LHSCst->isZero()))) {
+    BinaryOperator *BO =
+      dyn_cast<BinaryOperator>(LHSCC == ICmpInst::ICMP_NE ? Val : Val2);
+    ConstantInt *AndCst;
+    if (BO && match(BO, m_OneUse(m_And(m_Value(), m_ConstantInt(AndCst))))) {
+      APInt New = AndCst->getValue() | APInt::getSignBit(AndCst->getBitWidth());
+      BO->setOperand(1, ConstantInt::get(AndCst->getContext(), New));
+      return BO == Val ? LHS : RHS;
+    }
+  }
+
   // (icmp ult (X + CA), C1) | (icmp eq X, C2) -> (icmp ule (X + CA), C1)
   //   iff C2 + CA == C1.
   if (LHSCC == ICmpInst::ICMP_ULT && RHSCC == ICmpInst::ICMP_EQ) {