From 2f1cd85598d260e5567804460e87f8bee0c5e1e5 Mon Sep 17 00:00:00 2001
From: Bill Wendling <isanbard@gmail.com>
Date: Tue, 20 Sep 2011 19:10:24 +0000
Subject: [PATCH] When extracting a basic block that ends in an 'invoke'
 instruction, we need to extract its associated landing pad block as well.
 However, that landing pad block may have more than one predecessor. So split
 the landing pad block so that individual landing pads have only one
 predecessor.

This type of transformation may produce a false positive with bugpoint.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140173 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/IPO/LoopExtractor.cpp | 53 ++++++++++++++++++++++++----
 1 file changed, 46 insertions(+), 7 deletions(-)

diff --git a/lib/Transforms/IPO/LoopExtractor.cpp b/lib/Transforms/IPO/LoopExtractor.cpp
index 848944dc938..f90d1b32b35 100644
--- a/lib/Transforms/IPO/LoopExtractor.cpp
+++ b/lib/Transforms/IPO/LoopExtractor.cpp
@@ -23,6 +23,7 @@
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/FunctionUtils.h"
 #include "llvm/ADT/Statistic.h"
 #include <fstream>
@@ -53,12 +54,12 @@ namespace {
 
 char LoopExtractor::ID = 0;
 INITIALIZE_PASS_BEGIN(LoopExtractor, "loop-extract",
-                "Extract loops into new functions", false, false)
+                      "Extract loops into new functions", false, false)
 INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
 INITIALIZE_PASS_END(LoopExtractor, "loop-extract",
-                "Extract loops into new functions", false, false)
+                    "Extract loops into new functions", false, false)
 
 namespace {
   /// SingleLoopExtractor - For bugpoint.
@@ -149,6 +150,7 @@ namespace {
   /// BlocksToNotExtract list.
   class BlockExtractorPass : public ModulePass {
     void LoadFile(const char *Filename);
+    void SplitLandingPadPreds(Function *F);
 
     std::vector<BasicBlock*> BlocksToNotExtract;
     std::vector<std::pair<std::string, std::string> > BlocksToNotExtractByName;
@@ -171,8 +173,7 @@ INITIALIZE_PASS(BlockExtractorPass, "extract-blocks",
 // createBlockExtractorPass - This pass extracts all blocks (except those
 // specified in the argument list) from the functions in the module.
 //
-ModulePass *llvm::createBlockExtractorPass()
-{
+ModulePass *llvm::createBlockExtractorPass() {
   return new BlockExtractorPass();
 }
 
@@ -194,6 +195,37 @@ void BlockExtractorPass::LoadFile(const char *Filename) {
   }
 }
 
+/// SplitLandingPadPreds - The landing pad needs to be extracted with the invoke
+/// instruction. The critical edge breaker will refuse to break critical edges
+/// to a landing pad. So do them here. After this method runs, all landing pads
+/// should have only one predecessor.
+void BlockExtractorPass::SplitLandingPadPreds(Function *F) {
+  for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
+    InvokeInst *II = dyn_cast<InvokeInst>(I);
+    if (!II) continue;
+    BasicBlock *Parent = II->getParent();
+    BasicBlock *LPad = II->getUnwindDest();
+
+    // Look through the landing pad's predecessors. If one of them ends in an
+    // 'invoke', then we want to split the landing pad.
+    bool Split = false;
+    for (pred_iterator
+           PI = pred_begin(LPad), PE = pred_end(LPad); PI != PE; ++PI) {
+      BasicBlock *BB = *PI;
+      if (BB->isLandingPad() && BB != Parent &&
+          isa<InvokeInst>(Parent->getTerminator())) {
+        Split = true;
+        break;
+      }
+    }
+
+    if (!Split) continue;
+
+    SmallVector<BasicBlock*, 2> NewBBs;
+    SplitLandingPadPredecessors(LPad, Parent, ".1", ".2", 0, NewBBs);
+  }
+}
+
 bool BlockExtractorPass::runOnModule(Module &M) {
   std::set<BasicBlock*> TranslatedBlocksToNotExtract;
   for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
@@ -236,13 +268,20 @@ bool BlockExtractorPass::runOnModule(Module &M) {
   // Now that we know which blocks to not extract, figure out which ones we WANT
   // to extract.
   std::vector<BasicBlock*> BlocksToExtract;
-  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
+  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
+    SplitLandingPadPreds(&*F);
     for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
       if (!TranslatedBlocksToNotExtract.count(BB))
         BlocksToExtract.push_back(BB);
+  }
 
-  for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i)
-    ExtractBasicBlock(BlocksToExtract[i]);
+  for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i) {
+    SmallVector<BasicBlock*, 2> BlocksToExtractVec;
+    BlocksToExtractVec.push_back(BlocksToExtract[i]);
+    if (const InvokeInst *II = dyn_cast<InvokeInst>(BlocksToExtract[i]))
+      BlocksToExtractVec.push_back(II->getUnwindDest());
+    ExtractBasicBlock(BlocksToExtractVec);
+  }
 
   return !BlocksToExtract.empty();
 }