Factor some code into a new FoldSingleEntryPHINodes method.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60501 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 22 insertions, 10 deletions

diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 45cfe8f..431424e 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -54,6 +54,24 @@ void llvm::DeleteDeadBlock(BasicBlock *BB) {
   BB->eraseFromParent();
 }
 
+/// FoldSingleEntryPHINodes - We know that BB has one predecessor.  If there are
+/// any single-entry PHI nodes in it, fold them away.  This handles the case
+/// when all entries to the PHI nodes in a block are guaranteed equal, such as
+/// when the block has exactly one predecessor.
+void llvm::FoldSingleEntryPHINodes(BasicBlock *BB) {
+  if (!isa<PHINode>(BB->begin()))
+    return;
+  
+  while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
+    if (PN->getIncomingValue(0) != PN)
+      PN->replaceAllUsesWith(PN->getIncomingValue(0));
+    else
+      PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+    PN->eraseFromParent();
+  }
+}
+
+
 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
 /// if possible.  The return value indicates success or failure.
 bool llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) {
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index f4faeb3..d6465f5 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1101,10 +1101,7 @@ static bool FoldCondBranchOnPHI(BranchInst *BI) {
   
   // Degenerate case of a single entry PHI.
   if (PN->getNumIncomingValues() == 1) {
-    if (PN->getIncomingValue(0) != PN)
-      PN->replaceAllUsesWith(PN->getIncomingValue(0));
-    else
-      PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+    FoldSingleEntryPHINodes(PN->getParent());
     PN->eraseFromParent();
     return true;    
   }
diff --git a/lib/Transforms/Utils/UnrollLoop.cpp b/lib/Transforms/Utils/UnrollLoop.cpp
index 63493dc..caef7ec 100644
--- a/lib/Transforms/Utils/UnrollLoop.cpp
+++ b/lib/Transforms/Utils/UnrollLoop.cpp
@@ -25,13 +25,14 @@
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include <cstdio>
 
 using namespace llvm;
 
-/* TODO: Should these be here or in LoopUnroll? */
+// TODO: Should these be here or in LoopUnroll?
 STATISTIC(NumCompletelyUnrolled, "Number of loops completely unrolled");
 STATISTIC(NumUnrolled,    "Number of loops unrolled (completely or otherwise)");
 
@@ -68,11 +69,7 @@ static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI) {
   // multiple duplicate (but guaranteed to be equal) entries for the
   // incoming edges.  This occurs when there are multiple edges from
   // OnlyPred to OnlySucc.
-  //
-  while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
-    PN->replaceAllUsesWith(PN->getIncomingValue(0));
-    BB->getInstList().pop_front();  // Delete the phi node...
-  }
+  FoldSingleEntryPHINodes(BB);
 
   // Delete the unconditional branch from the predecessor...
   OnlyPred->getInstList().pop_back();