Optimize "icmp pred (urem X, Y), Y" --> true/false depending on pred. There's

more work to do here, "icmp ult (urem X, 10), 11" doesn't optimize away yet.
Fixes example 3 from PR9343!

llvm-svn: 126741

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 982dacb50bf..c23abb78089 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1434,6 +1434,9 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
         return ConstantInt::getTrue(CI->getContext());
       break;
     }
+
+    // TODO: integer div and rem with constant RHS all produce values in a
+    // constant range. We should check whether the comparison is a tautology.
   }
 
   // Compare of cast, for example (zext X) != 0 -> X != 0
@@ -1644,6 +1647,21 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     }
   }
 
+  if (LBO && match(LBO, m_URem(m_Value(), m_Specific(RHS)))) {
+    switch (Pred) {
+    default:
+      break;
+    case ICmpInst::ICMP_EQ:
+    case ICmpInst::ICMP_UGT:
+    case ICmpInst::ICMP_UGE:
+      return ConstantInt::getFalse(RHS->getContext());
+    case ICmpInst::ICMP_NE:
+    case ICmpInst::ICMP_ULT:
+    case ICmpInst::ICMP_ULE:
+      return ConstantInt::getTrue(RHS->getContext());
+    }
+  }
+
   // If the comparison is with the result of a select instruction, check whether
   // comparing with either branch of the select always yields the same value.
   if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))