[JumpThreading] PR36133 enable/disable DominatorTree for LVI analysis

Summary:
The LazyValueInfo pass caches a copy of the DominatorTree when available.
Whenever there are pending DominatorTree updates within JumpThreading's
DeferredDominance object we cannot use the cached DT for LVI analysis.
This commit adds the new methods enableDT() and disableDT() to LVI.
JumpThreading also sets the appropriate usage model before calling LVI
analysis methods.

Fixes https://bugs.llvm.org/show_bug.cgi?id=36133

Reviewers: sebpop, dberlin, kuhar

Reviewed by: sebpop, kuhar

Subscribers: uabelho, llvm-commits, aprantl, hiraditya, a.elovikov

Differential Revision: https://reviews.llvm.org/D42717

llvm-svn: 325356

1 files changed, 37 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 87a1d5e487e..8759563267b 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -425,6 +425,7 @@ bool JumpThreadingPass::runImpl(Function &F, TargetLibraryInfo *TLI_,
 
   LoopHeaders.clear();
   DDT->flush();
+  LVI->enableDT();
   return EverChanged;
 }
 
@@ -617,6 +618,10 @@ bool JumpThreadingPass::ComputeValueKnownInPredecessors(
     // "X < 4" and "X < 3" is known true but "X < 4" itself is not available.
     // Perhaps getConstantOnEdge should be smart enough to do this?
 
+    if (DDT->pending())
+      LVI->disableDT();
+    else
+      LVI->enableDT();
     for (BasicBlock *P : predecessors(BB)) {
       // If the value is known by LazyValueInfo to be a constant in a
       // predecessor, use that information to try to thread this block.
@@ -630,6 +635,10 @@ bool JumpThreadingPass::ComputeValueKnownInPredecessors(
 
   /// If I is a PHI node, then we know the incoming values for any constants.
   if (PHINode *PN = dyn_cast<PHINode>(I)) {
+    if (DDT->pending())
+      LVI->disableDT();
+    else
+      LVI->enableDT();
     for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
       Value *InVal = PN->getIncomingValue(i);
       if (Constant *KC = getKnownConstant(InVal, Preference)) {
@@ -759,6 +768,10 @@ bool JumpThreadingPass::ComputeValueKnownInPredecessors(
       const DataLayout &DL = PN->getModule()->getDataLayout();
       // We can do this simplification if any comparisons fold to true or false.
       // See if any do.
+      if (DDT->pending())
+        LVI->disableDT();
+      else
+        LVI->enableDT();
       for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
         BasicBlock *PredBB = PN->getIncomingBlock(i);
         Value *LHS = PN->getIncomingValue(i);
@@ -792,6 +805,10 @@ bool JumpThreadingPass::ComputeValueKnownInPredecessors(
 
       if (!isa<Instruction>(CmpLHS) ||
           cast<Instruction>(CmpLHS)->getParent() != BB) {
+        if (DDT->pending())
+          LVI->disableDT();
+        else
+          LVI->enableDT();
         for (BasicBlock *P : predecessors(BB)) {
           // If the value is known by LazyValueInfo to be a constant in a
           // predecessor, use that information to try to thread this block.
@@ -820,6 +837,10 @@ bool JumpThreadingPass::ComputeValueKnownInPredecessors(
             match(CmpLHS, m_Add(m_Value(AddLHS), m_ConstantInt(AddConst)))) {
           if (!isa<Instruction>(AddLHS) ||
               cast<Instruction>(AddLHS)->getParent() != BB) {
+            if (DDT->pending())
+              LVI->disableDT();
+            else
+              LVI->enableDT();
             for (BasicBlock *P : predecessors(BB)) {
               // If the value is known by LazyValueInfo to be a ConstantRange in
               // a predecessor, use that information to try to thread this
@@ -901,6 +922,10 @@ bool JumpThreadingPass::ComputeValueKnownInPredecessors(
   }
 
   // If all else fails, see if LVI can figure out a constant value for us.
+  if (DDT->pending())
+    LVI->disableDT();
+  else
+    LVI->enableDT();
   Constant *CI = LVI->getConstant(V, BB, CxtI);
   if (Constant *KC = getKnownConstant(CI, Preference)) {
     for (BasicBlock *Pred : predecessors(BB))
@@ -1102,6 +1127,10 @@ bool JumpThreadingPass::ProcessBlock(BasicBlock *BB) {
       // threading is concerned.
       assert(CondBr->isConditional() && "Threading on unconditional terminator");
 
+      if (DDT->pending())
+        LVI->disableDT();
+      else
+        LVI->enableDT();
       LazyValueInfo::Tristate Ret =
         LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
                             CondConst, CondBr);
@@ -1902,6 +1931,10 @@ bool JumpThreadingPass::ThreadEdge(BasicBlock *BB,
         << ", across block:\n    "
         << *BB << "\n");
 
+  if (DDT->pending())
+    LVI->disableDT();
+  else
+    LVI->enableDT();
   LVI->threadEdge(PredBB, BB, SuccBB);
 
   // We are going to have to map operands from the original BB block to the new
@@ -2371,6 +2404,10 @@ bool JumpThreadingPass::TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB) {
     // Now check if one of the select values would allow us to constant fold the
     // terminator in BB. We don't do the transform if both sides fold, those
     // cases will be threaded in any case.
+    if (DDT->pending())
+      LVI->disableDT();
+    else
+      LVI->enableDT();
     LazyValueInfo::Tristate LHSFolds =
         LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(1),
                                 CondRHS, Pred, BB, CondCmp);