[FIX] Bail out if there is a dependence cycle between invariant loads

  While the program cannot cause a dependence cycle between invariant
  loads, additional constraints (e.g., to ensure finite loops) can
  introduce them. It is hard to detect them in the SCoP description,
  thus we will only check for them at code generation time. If such a
  recursion is detected we will bail out the code generation and place a
  "false" runtime check to guarantee the original code is used.

  This fixes bug 25443.

llvm-svn: 252412

1 files changed, 8 insertions, 1 deletions

diff --git a/polly/lib/CodeGen/CodeGeneration.cpp b/polly/lib/CodeGen/CodeGeneration.cpp
index 7e6f044953d..95ddbfbbfd6 100644
--- a/polly/lib/CodeGen/CodeGeneration.cpp
+++ b/polly/lib/CodeGen/CodeGeneration.cpp
@@ -147,8 +147,15 @@ public:
     // parameters they reference. Afterwards, for the remaining parameters that
     // might reference the hoisted loads. Finally, build the runtime check
     // that might reference both hoisted loads as well as parameters.
+    // If the hoisting fails we have to bail and execute the original code.
     Builder.SetInsertPoint(SplitBlock->getTerminator());
-    NodeBuilder.preloadInvariantLoads();
+    if (!NodeBuilder.preloadInvariantLoads()) {
+      auto *FalseI1 = Builder.getFalse();
+      Builder.GetInsertBlock()->getTerminator()->setOperand(0, FalseI1);
+      isl_ast_node_free(AstRoot);
+      return true;
+    }
+
     NodeBuilder.addParameters(S.getContext());
 
     Value *RTC = buildRTC(Builder, NodeBuilder.getExprBuilder());