[IRCE] Fix SCEVExpander's usage in IRCE

When expanding exit conditions for pre- and postloops, we may end up expanding a
recurrency from the loop to in its loop's preheader. This produces incorrect IR.

This patch ensures that IRCE uses SCEVExpander correctly and only expands code which
is safe to expand in this particular location.

Differentian Revision: https://reviews.llvm.org/D39234

llvm-svn: 318381

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
index 01f7a969ba9..c83dc5d7a9d 100644
--- a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
@@ -1501,6 +1501,13 @@ bool LoopConstrainer::run() {
       ExitPreLoopAtSCEV = SE.getAddExpr(*SR.HighLimit, MinusOneS);
     }
 
+    if (!isSafeToExpandAt(ExitPreLoopAtSCEV, InsertPt, SE)) {
+      DEBUG(dbgs() << "irce: could not prove that it is safe to expand the"
+                   << " preloop exit limit " << *ExitPreLoopAtSCEV
+                   << " at block " << InsertPt->getParent()->getName() << "\n");
+      return false;
+    }
+
     ExitPreLoopAt = Expander.expandCodeFor(ExitPreLoopAtSCEV, IVTy, InsertPt);
     ExitPreLoopAt->setName("exit.preloop.at");
   }
@@ -1520,6 +1527,13 @@ bool LoopConstrainer::run() {
       ExitMainLoopAtSCEV = SE.getAddExpr(*SR.LowLimit, MinusOneS);
     }
 
+    if (!isSafeToExpandAt(ExitMainLoopAtSCEV, InsertPt, SE)) {
+      DEBUG(dbgs() << "irce: could not prove that it is safe to expand the"
+                   << " main loop exit limit " << *ExitMainLoopAtSCEV
+                   << " at block " << InsertPt->getParent()->getName() << "\n");
+      return false;
+    }
+
     ExitMainLoopAt = Expander.expandCodeFor(ExitMainLoopAtSCEV, IVTy, InsertPt);
     ExitMainLoopAt->setName("exit.mainloop.at");
   }