[Reassociate] Make sure EraseInst sets MadeChange

Summary:
EraseInst didn't report that it made IR changes through MadeChange.

It is essential that changes to the IR are reported correctly,
since for example ReassociatePass::run() will indicate that all
analyses are preserved otherwise.
And the CGPassManager determines if the CallGraph is up-to-date
based on status from InstructionCombiningPass::runOnFunction().

Reviewers: craig.topper, rnk, davide

Reviewed By: rnk, davide

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D34616

llvm-svn: 306368
diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index 6da551b..cdba006 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -1894,6 +1894,8 @@
         Op = Op->user_back();
       RedoInsts.insert(Op);
     }
+
+  MadeChange = true;
 }
 
 // Canonicalize expressions of the following form: