It is possible for several constants which aren't individually absorbing to

combine to the absorbing element.  Thanks to nbjoerg on IRC for pointing this 
out.

llvm-svn: 158399

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index ed7340f7e6d..66fa0744b84 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -629,8 +629,13 @@ static bool LinearizeExprTree(BinaryOperator *I,
   // Add any constants back into Ops, all globbed together and reduced to having
   // weight 1 for the convenience of users.
   Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType());
-  if (Cst && Cst != Identity)
+  if (Cst && Cst != Identity) {
+    // If combining multiple constants resulted in the absorber then the entire
+    // expression must evaluate to the absorber.
+    if (Cst == Absorber)
+      Ops.clear();
     Ops.push_back(std::make_pair(Cst, APInt(Bitwidth, 1)));
+  }
 
   // For nilpotent operations or addition there may be no operands, for example
   // because the expression was "X xor X" or consisted of 2^Bitwidth additions: