SSI construction should just go ahead and ignore instructions in unreachable

blocks.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79132 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 25 insertions, 2 deletions

diff --git a/lib/Transforms/Utils/SSI.cpp b/lib/Transforms/Utils/SSI.cpp
index 63ca354793..7736f08768 100644
--- a/lib/Transforms/Utils/SSI.cpp
+++ b/lib/Transforms/Utils/SSI.cpp
@@ -39,7 +39,7 @@ STATISTIC(NumPhiInserted, "Number of phi functions inserted");
 void SSI::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addRequired<DominanceFrontier>();
   AU.addRequired<DominatorTree>();
-  AU.setPreservesAll();
+  AU.setPreservesCFG();
 }
 
 bool SSI::runOnFunction(Function &F) {
@@ -121,7 +121,7 @@ void SSI::insertPhiFunctions(SmallVectorImpl<Instruction *> &value) {
     // Test if there were any sigmas for this variable
     if (needConstruction[i]) {
 
-      SmallPtrSet<BasicBlock *, 1> BB_visited;
+      SmallPtrSet<BasicBlock *, 16> BB_visited;
 
       // Insert phi functions if there is any sigma function
       while (!defsites[i].empty()) {
@@ -131,6 +131,10 @@ void SSI::insertPhiFunctions(SmallVectorImpl<Instruction *> &value) {
         defsites[i].pop_back();
         DominanceFrontier::iterator DF_BB = DF->find(BB);
 
+        // The BB is unreachable. Skip it.
+        if (DF_BB == DF->end())
+          continue; 
+
         // Iterates through all the dominance frontier of BB
         for (std::set<BasicBlock *>::iterator DF_BB_begin =
              DF_BB->second.begin(), DF_BB_end = DF_BB->second.end();
diff --git a/test/Transforms/SSI/2009-08-15-UnreachableBB.ll b/test/Transforms/SSI/2009-08-15-UnreachableBB.ll
new file mode 100644
index 0000000000..11a4f60b15
--- /dev/null
+++ b/test/Transforms/SSI/2009-08-15-UnreachableBB.ll
@@ -0,0 +1,19 @@
+; RUN: llvm-as < %s | opt -ssi-everything -disable-output
+
+declare fastcc i32 @ras_Empty(i8** nocapture) nounwind readonly
+
+define i32 @cc_Tautology() nounwind {
+entry:
+	unreachable
+
+cc_InitData.exit:		; No predecessors!
+	%0 = call fastcc i32 @ras_Empty(i8** undef) nounwind		; <i32> [#uses=1]
+	%1 = icmp eq i32 %0, 0		; <i1> [#uses=1]
+	br i1 %1, label %bb2, label %bb6
+
+bb2:		; preds = %cc_InitData.exit
+	unreachable
+
+bb6:		; preds = %cc_InitData.exit
+	ret i32 undef
+}