Make DSE only scan blocks that are reachable from the entry

block.  Other blocks may have pointer cycles that will crash
basicaa and other alias analyses.  In any case, there is no
point wasting cycles optimizing dead blocks.  This fixes 
rdar://7635088

llvm-svn: 95852

2 files changed, 21 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 320afa19d5f..09c01d31412 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -44,8 +44,14 @@ namespace {
 
     virtual bool runOnFunction(Function &F) {
       bool Changed = false;
+      
+      DominatorTree &DT = getAnalysis<DominatorTree>();
+      
       for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
-        Changed |= runOnBasicBlock(*I);
+        // Only check non-dead blocks.  Dead blocks may have strange pointer
+        // cycles that will confuse alias analysis.
+        if (DT.isReachableFromEntry(I))
+          Changed |= runOnBasicBlock(*I);
       return Changed;
     }
     
diff --git a/llvm/test/Transforms/DeadStoreElimination/crash.ll b/llvm/test/Transforms/DeadStoreElimination/crash.ll
index f89f8f5185c..6d8ba71b209 100644
--- a/llvm/test/Transforms/DeadStoreElimination/crash.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/crash.ll
@@ -41,3 +41,17 @@ bb14:                                             ; preds = %bb4
 }
 
 declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32) nounwind
+
+
+; rdar://7635088
+define i32 @test3() {
+entry:
+  ret i32 0
+  
+dead:
+  %P2 = getelementptr i32 *%P2, i32 52
+  %Q2 = getelementptr i32 *%Q2, i32 52
+  store i32 4, i32* %P2
+  store i32 4, i32* %Q2
+  br label %dead
+}
\ No newline at end of file