A better fix for PR2503 that doesn't pessimize GVN in the presence of unreachable blocks.

llvm-svn: 53032

2 files changed, 5 insertions, 13 deletions

diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index 1cd16bb06de..2012ab473c9 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -19,7 +19,6 @@
 #include "llvm/Instructions.h"
 #include "llvm/Function.h"
 #include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Analysis/Dominators.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetData.h"
@@ -83,7 +82,6 @@ void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesAll();
   AU.addRequiredTransitive<AliasAnalysis>();
   AU.addRequiredTransitive<TargetData>();
-  AU.addRequiredTransitive<DominatorTree>();
 }
 
 /// getCallSiteDependency - Private helper for finding the local dependencies
@@ -224,17 +222,6 @@ void MemoryDependenceAnalysis::nonLocalHelper(Instruction* query,
       continue;
     }
     
-    // Don't recur upwards if the current block is unreachable.
-    // Instead, mark it as having no dependency on this path,
-    // which will block optzns from occuring.  For this reason,
-    // eliminating unreachable blocks before running a memdep
-    // based optimization is recommended.
-    DominatorTree& DT = getAnalysis<DominatorTree>();
-    if (!DT.isReachableFromEntry(BB)) {
-      resp.insert(std::make_pair(BB, None));
-      continue;
-    }
-    
     // If we didn't find anything, recurse on the precessors of this block
     // Only do this for blocks with a small number of predecessors.
     bool predOnStack = false;
diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index 5564dbde1bf..590227c27f9 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -808,6 +808,11 @@ Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
   DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
   if (V != Phis.end() && !top_level) return V->second;
   
+  if (!getAnalysis<DominatorTree>().isReachableFromEntry(BB)) {
+    Phis[BB] = UndefValue::get(orig->getType());
+    return UndefValue::get(orig->getType());
+  }
+  
   BasicBlock* singlePred = BB->getSinglePredecessor();
   if (singlePred) {
     Value *ret = GetValueForBlock(singlePred, orig, Phis);