[LICM] Avoind store sinking if no preheader is available

Load instructions are inserted into loop preheaders when sinking stores
and later removed if not used by the SSA updater. Avoid sinking if the
loop has no preheader and avoid crashes. This fixes one more side effect
of not handling indirectbr instructions properly on LoopSimplify.

llvm-svn: 223119

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index c706248267f..99725b5f738 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -847,8 +847,10 @@ void LICM::PromoteAliasSet(AliasSet &AS,
           return;
         // Don't sink stores from loops without dedicated block exits. Exits
         // containing indirect branches are not transformed by loop simplify,
-        // make sure we catch that.
-        if (!HasDedicatedExits)
+        // make sure we catch that. An additional load may be generated in the
+        // preheader for SSA updater, so also avoid sinking when no preheader
+        // is available.
+        if (!HasDedicatedExits || !Preheader)
           return;
 
         // Note that we only check GuaranteedToExecute inside the store case