Clear the SCEVExpander's insertion point after making deletions,

so that the SCEVExpander doesn't retain a dangling pointer as its
insert position. The dangling pointer in this case wasn't ever used
to insert new instructions, but it was causing trouble with
SCEVExpander's code for automatically advancing its insert position
past debug intrinsics.

This fixes use-after-free errors that valgrind noticed in
test/Transforms/IndVarSimplify/2007-06-06-DeleteDanglesPtr.ll and
test/Transforms/IndVarSimplify/exit_value_tests.ll.

llvm-svn: 99036

2 files changed, 11 insertions, 0 deletions

diff --git a/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h b/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
index 828709404b1..dc9b73bd566 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
@@ -104,6 +104,13 @@ namespace llvm {
     /// is useful for late optimization passes.
     void disableCanonicalMode() { CanonicalMode = false; }
 
+    /// clearInsertPoint - Clear the current insertion point. This is useful
+    /// if the instruction that had been serving as the insertion point may
+    /// have been deleted.
+    void clearInsertPoint() {
+      Builder.ClearInsertionPoint();
+    }
+
   private:
     LLVMContext &getContext() const { return SE.getContext(); }
 
diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index de93e9f621f..eb04d9401fb 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -307,6 +307,10 @@ void IndVarSimplify::RewriteLoopExitValues(Loop *L,
       }
     }
   }
+
+  // The insertion point instruction may have been deleted; clear it out
+  // so that the rewriter doesn't trip over it later.
+  Rewriter.clearInsertPoint();
 }
 
 void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {