BBVectorize: Fix an invalid reference bug

This fixes PR15289. This bug was introduced (recently) in r175215; collecting
all std::vector references for candidate pairs to delete at once is invalid
because subsequent lookups in the owning DenseMap could invalidate the
references.

bugpoint was able to reduce a useful test case. Unfortunately, because whether
or not this asserts depends on memory layout, this test case will sometimes
appear to produce valid output. Nevertheless, running under valgrind will
reveal the error.

llvm-svn: 175397

1 files changed, 7 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Vectorize/BBVectorize.cpp b/llvm/lib/Transforms/Vectorize/BBVectorize.cpp
index 1773cff3bb7..76365417aa8 100644
--- a/llvm/lib/Transforms/Vectorize/BBVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/BBVectorize.cpp
@@ -2164,10 +2164,7 @@ namespace {
                *S->second << "\n");
 
         // Remove all candidate pairs that have values in the chosen dag.
-        std::vector<Value *> &KK = CandidatePairs[S->first],
-                             &LL = CandidatePairs2[S->second],
-                             &MM = CandidatePairs[S->second],
-                             &NN = CandidatePairs2[S->first];
+        std::vector<Value *> &KK = CandidatePairs[S->first];
         for (std::vector<Value *>::iterator K = KK.begin(), KE = KK.end();
              K != KE; ++K) {
           if (*K == S->second)
@@ -2175,6 +2172,8 @@ namespace {
 
           CandidatePairsSet.erase(ValuePair(S->first, *K));
         }
+
+        std::vector<Value *> &LL = CandidatePairs2[S->second];
         for (std::vector<Value *>::iterator L = LL.begin(), LE = LL.end();
              L != LE; ++L) {
           if (*L == S->first)
@@ -2182,11 +2181,15 @@ namespace {
 
           CandidatePairsSet.erase(ValuePair(*L, S->second));
         }
+
+        std::vector<Value *> &MM = CandidatePairs[S->second];
         for (std::vector<Value *>::iterator M = MM.begin(), ME = MM.end();
              M != ME; ++M) {
           assert(*M != S->first && "Flipped pair in candidate list?");
           CandidatePairsSet.erase(ValuePair(S->second, *M));
         }
+
+        std::vector<Value *> &NN = CandidatePairs2[S->first];
         for (std::vector<Value *>::iterator N = NN.begin(), NE = NN.end();
              N != NE; ++N) {
           assert(*N != S->second && "Flipped pair in candidate list?");