Revert "[SimlifyCFG] Prevent passes from destroying canonical loop structure, especially for nested loops"

This reverts commit r264596.

It does not compile.

llvm-svn: 264604

3 files changed, 8 insertions, 34 deletions

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 2def0b54c6d..c79e756f572 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -245,13 +245,10 @@ bool JumpThreading::runOnFunction(Function &F) {
       // Can't thread an unconditional jump, but if the block is "almost
       // empty", we can replace uses of it with uses of the successor and make
       // this dead.
-      // We should not eliminate the loop header either, because eliminating
-      // a loop header might later prevent LoopSimplify from transforming nested
-      // loops into simplified form.
       if (BI && BI->isUnconditional() &&
           BB != &BB->getParent()->getEntryBlock() &&
           // If the terminator is the only non-phi instruction, try to nuke it.
-          BB->getFirstNonPHIOrDbg()->isTerminator() && !LoopHeaders.count(BB)) {
+          BB->getFirstNonPHIOrDbg()->isTerminator()) {
         // Since TryToSimplifyUncondBranchFromEmptyBlock may delete the
         // block, we have to make sure it isn't in the LoopHeaders set.  We
         // reinsert afterward if needed.
diff --git a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
index 72ce7693ec0..687d388701e 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -28,7 +28,6 @@
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
-#include "llvm/Analysis/CFG.h"
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constants.h"
@@ -131,20 +130,13 @@ static bool iterativelySimplifyCFG(Function &F, const TargetTransformInfo &TTI,
                                    AssumptionCache *AC,
                                    unsigned BonusInstThreshold) {
   bool Changed = false;
-  bool LocalChange = true; 
-
-  SmallVector<std::pair<const BasicBlock *, const BasicBlock *>, 32> Edges;
-  FindFunctionBackedges(F, Edges);
-  SmallPtrSet<BasicBlock *, 16> LoopHeaders;
-  for (unsigned i = 0, e = Edges.size(); i != e; ++i)
-    LoopHeaders.insert(const_cast<BasicBlock *>(Edges[i].second));
-
+  bool LocalChange = true;
   while (LocalChange) {
     LocalChange = false;
 
     // Loop over all of the basic blocks and remove them if they are unneeded.
     for (Function::iterator BBIt = F.begin(); BBIt != F.end(); ) {
-      if (SimplifyCFG(&*BBIt++, TTI, BonusInstThreshold, AC, &LoopHeaders)) {
+      if (SimplifyCFG(&*BBIt++, TTI, BonusInstThreshold, AC)) {
         LocalChange = true;
         ++NumSimpl;
       }
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 197ac510949..75d42617a6a 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -135,7 +135,6 @@ class SimplifyCFGOpt {
   const DataLayout &DL;
   unsigned BonusInstThreshold;
   AssumptionCache *AC;
-  SmallPtrSetImpl<BasicBlock *> *LoopHeaders;
   Value *isValueEqualityComparison(TerminatorInst *TI);
   BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
                                std::vector<ValueEqualityComparisonCase> &Cases);
@@ -158,10 +157,8 @@ class SimplifyCFGOpt {
 
 public:
   SimplifyCFGOpt(const TargetTransformInfo &TTI, const DataLayout &DL,
-                 unsigned BonusInstThreshold, AssumptionCache *AC,
-                 SmallPtrSetImpl<BasicBlock *> *LoopHeaders)
-      : TTI(TTI), DL(DL), BonusInstThreshold(BonusInstThreshold), AC(AC),
-        LoopHeaders(LoopHeaders) {}
+                 unsigned BonusInstThreshold, AssumptionCache *AC)
+      : TTI(TTI), DL(DL), BonusInstThreshold(BonusInstThreshold), AC(AC) {}
   bool run(BasicBlock *BB);
 };
 }
@@ -3365,7 +3362,6 @@ bool SimplifyCFGOpt::SimplifySingleResume(ResumeInst *RI) {
 
   // The landingpad is now unreachable.  Zap it.
   BB->eraseFromParent();
-  if (LoopHeaders) LoopHeaders->erase(BB);
   return true;
 }
 
@@ -3484,7 +3480,6 @@ static bool removeEmptyCleanup(CleanupReturnInst *RI) {
 
   // The cleanup pad is now unreachable.  Zap it.
   BB->eraseFromParent();
-  if (LoopHeaders) LoopHeaders->erase(BB);
   return true;
 }
 
@@ -3565,11 +3560,9 @@ bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
     }
 
     // If we eliminated all predecessors of the block, delete the block now.
-    if (pred_empty(BB)) {
+    if (pred_empty(BB))
       // We know there are no successors, so just nuke the block.
       BB->eraseFromParent();
-      if (LoopHeaders) LoopHeaders->erase(BB);
-    }
 
     return true;
   }
@@ -3726,7 +3719,6 @@ bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
       BB != &BB->getParent()->getEntryBlock()) {
     // We know there are no successors, so just nuke the block.
     BB->eraseFromParent();
-    if (LoopHeaders) LoopHeaders->erase(BB);
     return true;
   }
 
@@ -5070,14 +5062,8 @@ bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
     return true;
 
   // If the Terminator is the only non-phi instruction, simplify the block.
-  // if LoopHeader is provided, check if the block is a loop header
-  // (This is for early invocations before loop simplify and vectorization
-  // to keep canonical loop forms for nested loops.
-  // These blocks can be eliminated when the pass is invoked later 
-  // in the back-end.)
   BasicBlock::iterator I = BB->getFirstNonPHIOrDbg()->getIterator();
   if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
-      (!LoopHeaders || (LoopHeaders && !LoopHeaders->count(BB))) &&
       TryToSimplifyUncondBranchFromEmptyBlock(BB))
     return true;
 
@@ -5357,8 +5343,7 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
 /// of the CFG.  It returns true if a modification was made.
 ///
 bool llvm::SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI,
-                       unsigned BonusInstThreshold, AssumptionCache *AC,
-                       SmallPtrSetImpl<BasicBlock *> *LoopHeaders) {
+                       unsigned BonusInstThreshold, AssumptionCache *AC) {
   return SimplifyCFGOpt(TTI, BB->getModule()->getDataLayout(),
-                        BonusInstThreshold, AC, LoopHeaders).run(BB);
+                        BonusInstThreshold, AC).run(BB);
 }