From: Owen Anderson <resistor@mac.com>
Date: Thu, 17 Jul 2008 19:42:29 +0000 (+0000)
Subject: Make MergeBlockIntoPredecessor more aggressive when the same successor appears
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=commitdiff_plain;h=11f2ec8eb534502a0d5b7e3c13c1a38e877876b2

Make MergeBlockIntoPredecessor more aggressive when the same successor appears
more than once.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53731 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/llvm/Transforms/Utils/BasicBlockUtils.h b/include/llvm/Transforms/Utils/BasicBlockUtils.h
index f1a7a264176..5b367015afa 100644
--- a/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ b/include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -27,7 +27,7 @@ class Pass;
 
 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
 /// if possible.  The return value indicates success or failure.
-bool MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P);
+bool MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P = 0);
 
 // ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
 // with a value, then remove and delete the original instruction.
diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 02eb4d6f60a..d889422992b 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -26,15 +26,30 @@ using namespace llvm;
 /// 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) {
+  pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
   // Can't merge the entry block.
   if (pred_begin(BB) == pred_end(BB)) return false;
-  // Can't merge if there are multiple preds.
-  if (++pred_begin(BB) != pred_end(BB)) return false;
   
-  BasicBlock* PredBB = *pred_begin(BB);
+  BasicBlock *PredBB = *PI++;
+  for (; PI != PE; ++PI)  // Search all predecessors, see if they are all same
+    if (*PI != PredBB) {
+      PredBB = 0;       // There are multiple different predecessors...
+      break;
+    }
   
-  // Can't merge if the edge is critical.
-  if (PredBB->getTerminator()->getNumSuccessors() != 1) return false;
+  // Can't merge if there are multiple predecessors.
+  if (!PredBB) return false;
+  
+  succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
+  BasicBlock* OnlySucc = BB;
+  for (; SI != SE; ++SI)
+    if (*SI != OnlySucc) {
+      OnlySucc = 0;     // There are multiple distinct successors!
+      break;
+    }
+  
+  // Can't merge if there are multiple successors.
+  if (!OnlySucc) return false;
   
   // Begin by getting rid of unneeded PHIs.
   while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
@@ -52,6 +67,10 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) {
   // source...
   BB->replaceAllUsesWith(PredBB);
   
+  // Inherit predecessors name if it exists.
+  if (!PredBB->hasName())
+    PredBB->takeName(BB);
+  
   // Finally, erase the old block and update dominator info.
   if (P) {
     if (DominatorTree* DT = P->getAnalysisToUpdate<DominatorTree>()) {