LoopSimplify bug fix. Handle indirect loop back edges.

Do not call SplitBlockPredecessors on a loop preheader when one of the
predecessors is an indirectbr. Otherwise, you will hit this assert:
!isa<IndirectBrInst>(Preds[i]->getTerminator()) && "Cannot split an edge from an IndirectBrInst"

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153134 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 49 insertions, 5 deletions

diff --git a/lib/Transforms/Utils/LoopSimplify.cpp b/lib/Transforms/Utils/LoopSimplify.cpp
index 1b6a19d9b6..0bc185d8b7 100644
--- a/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/lib/Transforms/Utils/LoopSimplify.cpp
@@ -538,8 +538,7 @@ void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
 ///
 Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM,
                                        BasicBlock *Preheader) {
-  // Don't try to separate loops without a preheader (this excludes
-  // loop headers which are targeted by an indirectbr).
+  // Don't try to separate loops without a preheader.
   if (!Preheader)
     return 0;
 
@@ -554,11 +553,15 @@ Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM,
   // handles the case when a PHI node has multiple instances of itself as
   // arguments.
   SmallVector<BasicBlock*, 8> OuterLoopPreds;
-  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
     if (PN->getIncomingValue(i) != PN ||
-        !L->contains(PN->getIncomingBlock(i)))
+        !L->contains(PN->getIncomingBlock(i))) {
+      // We can't split indirectbr edges.
+      if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
+        return 0;
       OuterLoopPreds.push_back(PN->getIncomingBlock(i));
-
+    }
+  }
   DEBUG(dbgs() << "LoopSimplify: Splitting out a new outer loop\n");
 
   // If ScalarEvolution is around and knows anything about values in
diff --git a/test/Transforms/LoopSimplify/2012-03-20-indirectbr.ll b/test/Transforms/LoopSimplify/2012-03-20-indirectbr.ll
new file mode 100644
index 0000000000..9c805da485
--- /dev/null
+++ b/test/Transforms/LoopSimplify/2012-03-20-indirectbr.ll
@@ -0,0 +1,41 @@
+; RUN: opt < %s -loop-simplify -S | FileCheck %s
+
+; Make sure the preheader exists.
+; CHECK: sw.bb103:
+; CHECK: indirectbr {{.*}}label %while.cond112
+; CHECK: while.cond112:
+; But the tail is not split.
+; CHECK: for.body:
+; CHECK: indirectbr {{.*}}label %while.cond112
+define fastcc void @build_regex_nfa() nounwind uwtable ssp {
+entry:
+  indirectbr i8* blockaddress(@build_regex_nfa, %while.cond), [label %while.cond]
+
+while.cond:                                       ; preds = %if.then439, %entry
+  indirectbr i8* blockaddress(@build_regex_nfa, %sw.bb103), [label %do.body785, label %sw.bb103]
+
+sw.bb103:                                         ; preds = %while.body
+  indirectbr i8* blockaddress(@build_regex_nfa, %while.cond112), [label %while.cond112]
+
+while.cond112:                                    ; preds = %for.body, %for.cond.preheader, %sw.bb103
+  %pc.0 = phi i8 [ -1, %sw.bb103 ], [ 0, %for.body ], [ %pc.0, %for.cond.preheader ]
+  indirectbr i8* blockaddress(@build_regex_nfa, %Lsetdone), [label %sw.bb118, label %Lsetdone]
+
+sw.bb118:                                         ; preds = %while.cond112
+  indirectbr i8* blockaddress(@build_regex_nfa, %for.cond.preheader), [label %Lerror.loopexit, label %for.cond.preheader]
+
+for.cond.preheader:                               ; preds = %sw.bb118
+  indirectbr i8* blockaddress(@build_regex_nfa, %for.body), [label %while.cond112, label %for.body]
+
+for.body:                                         ; preds = %for.body, %for.cond.preheader
+  indirectbr i8* blockaddress(@build_regex_nfa, %for.body), [label %while.cond112, label %for.body]
+
+Lsetdone:                                         ; preds = %while.cond112
+  unreachable
+
+do.body785:                                       ; preds = %while.cond, %while.body
+  ret void
+
+Lerror.loopexit:                                  ; preds = %sw.bb118
+  unreachable
+}