[GVN] Preserve loop related analysis/canonical forms.

LoopInfo can be easily preserved by passing it to the functions that
modify the CFG (SplitCriticalEdge and MergeBlockIntoPredecessor.
SplitCriticalEdge also preserves LoopSimplify and LCSSA form when when passing in
LoopInfo. The test case shows that we preserve LoopSimplify and
LoopInfo. Adding addPreservedID(LCSSAID) did not preserve LCSSA for some
reason.

Also I am not sure if it is possible to preserve those in the new pass
manager, as they aren't analysis passes.

Reviewers: reames, hfinkel, davide, jdoerfert

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D65137

llvm-svn: 367332

llvm/include/llvm/Analysis/CFG.h

@@ -46,6 +46,8 @@ unsigned GetSuccessorNumber(const BasicBlock *BB, const BasicBlock *Succ);
 ///
 bool isCriticalEdge(const Instruction *TI, unsigned SuccNum,
                     bool AllowIdenticalEdges = false);
+bool isCriticalEdge(const Instruction *TI, const BasicBlock *Succ,
+                    bool AllowIdenticalEdges = false);
 
 /// Determine whether instruction 'To' is reachable from 'From', without passing
 /// through any blocks in ExclusionSet, returning true if uncertain.

llvm/include/llvm/Transforms/Scalar/GVN.h

@@ -159,6 +159,7 @@ private:
   SetVector<BasicBlock *> DeadBlocks;
   OptimizationRemarkEmitter *ORE;
   ImplicitControlFlowTracking *ICF;
+  LoopInfo *LI;
 
   ValueTable VN;
 

llvm/lib/Analysis/CFG.cpp

@@ -87,11 +87,18 @@ unsigned llvm::GetSuccessorNumber(const BasicBlock *BB,
 /// with multiple predecessors.
 bool llvm::isCriticalEdge(const Instruction *TI, unsigned SuccNum,
                           bool AllowIdenticalEdges) {
-  assert(TI->isTerminator() && "Must be a terminator to have successors!");
   assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
+  return isCriticalEdge(TI, TI->getSuccessor(SuccNum), AllowIdenticalEdges);
+}
+
+bool llvm::isCriticalEdge(const Instruction *TI, const BasicBlock *Dest,
+                          bool AllowIdenticalEdges) {
+  assert(TI->isTerminator() && "Must be a terminator to have successors!");
   if (TI->getNumSuccessors() == 1) return false;
 
-  const BasicBlock *Dest = TI->getSuccessor(SuccNum);
+  assert(find(predecessors(Dest), TI->getParent()) != pred_end(Dest) &&
+         "No edge between TI's block and Dest.");
+
   const_pred_iterator I = pred_begin(Dest), E = pred_end(Dest);
 
   // If there is more than one predecessor, this is a critical edge...

llvm/lib/Transforms/Scalar/GVN.cpp

@@ -70,6 +70,7 @@
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/SSAUpdater.h"
@@ -626,6 +627,8 @@ PreservedAnalyses GVN::run(Function &F, FunctionAnalysisManager &AM) {
   PA.preserve<DominatorTreeAnalysis>();
   PA.preserve<GlobalsAA>();
   PA.preserve<TargetLibraryAnalysis>();
+  if (LI)
+    PA.preserve<LoopAnalysis>();
   return PA;
 }
 
@@ -1976,6 +1979,7 @@ bool GVN::runImpl(Function &F, AssumptionCache &RunAC, DominatorTree &RunDT,
   MD = RunMD;
   ImplicitControlFlowTracking ImplicitCFT(DT);
   ICF = &ImplicitCFT;
+  this->LI = LI;
   VN.setMemDep(MD);
   ORE = RunORE;
   InvalidBlockRPONumbers = true;
@@ -2335,7 +2339,7 @@ bool GVN::performPRE(Function &F) {
 /// the block inserted to the critical edge.
 BasicBlock *GVN::splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ) {
   BasicBlock *BB =
-      SplitCriticalEdge(Pred, Succ, CriticalEdgeSplittingOptions(DT));
+      SplitCriticalEdge(Pred, Succ, CriticalEdgeSplittingOptions(DT, LI));
   if (MD)
     MD->invalidateCachedPredecessors();
   InvalidBlockRPONumbers = true;
@@ -2350,7 +2354,7 @@ bool GVN::splitCriticalEdges() {
   do {
     std::pair<Instruction *, unsigned> Edge = toSplit.pop_back_val();
     SplitCriticalEdge(Edge.first, Edge.second,
-                      CriticalEdgeSplittingOptions(DT));
+                      CriticalEdgeSplittingOptions(DT, LI));
   } while (!toSplit.empty());
   if (MD) MD->invalidateCachedPredecessors();
   InvalidBlockRPONumbers = true;
@@ -2456,18 +2460,26 @@ void GVN::addDeadBlock(BasicBlock *BB) {
     if (DeadBlocks.count(B))
       continue;
 
+    // First, split the critical edges. This might also create additional blocks
+    // to preserve LoopSimplify form and adjust edges accordingly.
     SmallVector<BasicBlock *, 4> Preds(pred_begin(B), pred_end(B));
     for (BasicBlock *P : Preds) {
       if (!DeadBlocks.count(P))
         continue;
 
-      if (isCriticalEdge(P->getTerminator(), GetSuccessorNumber(P, B))) {
+      if (llvm::any_of(successors(P),
+                       [B](BasicBlock *Succ) { return Succ == B; }) &&
+          isCriticalEdge(P->getTerminator(), B)) {
         if (BasicBlock *S = splitCriticalEdges(P, B))
           DeadBlocks.insert(P = S);
       }
+    }
 
-      for (BasicBlock::iterator II = B->begin(); isa<PHINode>(II); ++II) {
-        PHINode &Phi = cast<PHINode>(*II);
+    // Now undef the incoming values from the dead predecessors.
+    for (BasicBlock *P : predecessors(B)) {
+      if (!DeadBlocks.count(P))
+        continue;
+      for (PHINode &Phi : B->phis()) {
         Phi.setIncomingValueForBlock(P, UndefValue::get(Phi.getType()));
         if (MD)
           MD->invalidateCachedPointerInfo(&Phi);
@@ -2556,6 +2568,7 @@ public:
     AU.addRequired<AssumptionCacheTracker>();
     AU.addRequired<DominatorTreeWrapperPass>();
     AU.addRequired<TargetLibraryInfoWrapperPass>();
+    AU.addRequired<LoopInfoWrapperPass>();
     if (!NoMemDepAnalysis)
       AU.addRequired<MemoryDependenceWrapperPass>();
     AU.addRequired<AAResultsWrapperPass>();
@@ -2563,6 +2576,8 @@ public:
     AU.addPreserved<DominatorTreeWrapperPass>();
     AU.addPreserved<GlobalsAAWrapperPass>();
     AU.addPreserved<TargetLibraryInfoWrapperPass>();
+    AU.addPreserved<LoopInfoWrapperPass>();
+    AU.addPreservedID(LoopSimplifyID);
     AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
   }
 

llvm/test/Transforms/GVN/PRE/2011-06-01-NonLocalMemdepMiscompile.ll

@@ -50,8 +50,14 @@ bb15:
   %tmp18 = icmp eq i8 %tmp17, 0
   br label %bb19
 
-; CHECK: bb15:
-; CHECK: %tmp17 = phi i8 [ %tmp17.pre, %bb1.bb15_crit_edge ], [ %tmp8, %bb6 ]
+; CHECK-LABEL: bb6:
+; CHECK:         br i1 undef, label %bb15split, label %bb10
+
+; CHECK-LABEL: bb15split:                                        ; preds = %bb6
+; CHECK-NEXT:    br label %bb15
+
+; CHECK-LABEL: bb15:
+; CHECK:         %tmp17 = phi i8 [ %tmp8, %bb15split ], [ %tmp17.pre, %bb1.bb15_crit_edge ]
 
 bb19:                                             ; preds = %bb15
   ret i1 %tmp18

llvm/test/Transforms/GVN/preserve-analysis.ll

@@ -0,0 +1,56 @@
+; RUN: opt < %s -debug-pass=Structure -indvars -gvn -indvars 2>&1 -S | FileCheck --check-prefix=CHECK --check-prefix=IR %s
+; RUN: opt < %s -debug-pass-manager -passes='require<domtree>,loop(simplify-cfg),gvn,loop(indvars)' 2>&1 -S | FileCheck --check-prefix=NEW-PM --check-prefix=IR %s
+
+; Check CFG-only analysis are preserved by SCCP by running it between 2
+; loop-vectorize runs.
+
+; CHECK: Dominator Tree Construction
+; CHECK: Natural Loop Information
+; CHECK: Canonicalize natural loops
+; CHECK: LCSSA Verifier
+; CHECK: Loop-Closed SSA Form Pass
+; CHECK: Global Value Numbering
+; CHECK-NOT: Dominator Tree Construction
+; CHECK-NOT: Natural Loop Information
+; CHECK-NOT: Canonicalize natural loops
+
+; NEW-PM-DAG: Running analysis: LoopAnalysis on test
+; NEW-PM-DAG: Running analysis: DominatorTreeAnalysis on test
+; NEW-PM: Running pass: GVN on test
+; NEW-PM-NOT: Running analysis: LoopAnalysis on test
+; NEW-PM-NOT: Running analysis: DominatorTreeAnalysis on test
+
+declare i1 @cond()
+declare void @dostuff()
+
+define i32 @test() {
+; IR-LABEL: define i32 @test()
+; IR-LABEL: header:
+; IR:         br i1 false, label %then, label %latch
+; IR-LABEL: then:
+; IR-NEXT:   call void @dostuff()
+; IR-NEXT:   br label %latch
+entry:
+  %res = add i32 1, 10
+  br label %header
+
+header:
+  %iv = phi i32 [ %res, %entry ], [ 0, %latch ]
+  %ic = icmp eq i32 %res, 99
+  br i1 %ic, label %then, label %latch
+
+then:
+  br label %then.2
+
+then.2:
+  call void @dostuff()
+  br label %latch
+
+
+latch:
+  %ec = call i1 @cond()
+  br i1 %ec, label %exit, label %header
+
+exit:
+  ret i32 %iv
+}