From 795cf5efba4255cadd0bfde0e9d3dec65e96dd50 Mon Sep 17 00:00:00 2001
From: Bill Wendling <isanbard@gmail.com>
Date: Wed, 17 Aug 2011 21:32:02 +0000
Subject: [PATCH] Disable PRE for landing pads.

PRE needs the landing pads to have their critical edges split. Doing this for a
landing pad is non-trivial. Abandon the attempt to perform PRE when we come
across a landing pad. (Reviewed by Owen!)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137876 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/GVN.cpp | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index 81241693558..9785b318924 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -1446,8 +1446,8 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
   for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
     Blockers.insert(UnavailableBlocks[i]);
 
-  // Lets find first basic block with more than one predecessor.  Walk backwards
-  // through predecessors if needed.
+  // Let's find the first basic block with more than one predecessor.  Walk
+  // backwards through predecessors if needed.
   BasicBlock *LoadBB = LI->getParent();
   BasicBlock *TmpBB = LoadBB;
 
@@ -1519,10 +1519,19 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
               << Pred->getName() << "': " << *LI << '\n');
         return false;
       }
+
+      if (LoadBB->isLandingPad()) {
+        DEBUG(dbgs()
+              << "COULD NOT PRE LOAD BECAUSE OF LANDING PAD CRITICAL EDGE '"
+              << Pred->getName() << "': " << *LI << '\n');
+        return false;
+      }
+
       unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB);
       NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum));
     }
   }
+
   if (!NeedToSplit.empty()) {
     toSplit.append(NeedToSplit.begin(), NeedToSplit.end());
     return false;
@@ -2071,6 +2080,9 @@ bool GVN::performPRE(Function &F) {
     // Nothing to PRE in the entry block.
     if (CurrentBlock == &F.getEntryBlock()) continue;
 
+    // Don't perform PRE on a landing pad.
+    if (CurrentBlock->isLandingPad()) continue;
+
     for (BasicBlock::iterator BI = CurrentBlock->begin(),
          BE = CurrentBlock->end(); BI != BE; ) {
       Instruction *CurInst = BI++;