Reapply "[LV] Enable vectorization of loops with conditional stores by default"

This patch reapplies r289863. The original patch was reverted because it
exposed a bug causing the loop vectorizer to crash in the Python runtime on
PPC. The underlying issue was fixed with r289958.

llvm-svn: 289975
diff --git a/llvm/test/Transforms/LoopVectorize/conditional-assignment.ll b/llvm/test/Transforms/LoopVectorize/conditional-assignment.ll
index 2222a26..25d6111 100644
--- a/llvm/test/Transforms/LoopVectorize/conditional-assignment.ll
+++ b/llvm/test/Transforms/LoopVectorize/conditional-assignment.ll
@@ -1,5 +1,5 @@
-; RUN: opt < %s -loop-vectorize -S -pass-remarks-missed='loop-vectorize' -pass-remarks-analysis='loop-vectorize' 2>&1 | FileCheck %s
-; RUN: opt < %s -passes=loop-vectorize -S -pass-remarks-missed='loop-vectorize' -pass-remarks-analysis='loop-vectorize' 2>&1 | FileCheck %s
+; RUN: opt < %s -enable-cond-stores-vec=false -loop-vectorize -S -pass-remarks-missed='loop-vectorize' -pass-remarks-analysis='loop-vectorize' 2>&1 | FileCheck %s
+; RUN: opt < %s -enable-cond-stores-vec=false -passes=loop-vectorize -S -pass-remarks-missed='loop-vectorize' -pass-remarks-analysis='loop-vectorize' 2>&1 | FileCheck %s
 
 ; CHECK: remark: source.c:2:8: loop not vectorized: store that is conditionally executed prevents vectorization