AMDGPU: Fix annotating loops with nested loop conditions

If the branch condition for a loop was a phi which itself
was fed from a phi from a loop, it isn't safe to try
to delete the phi until after the loop is handled.

llvm-svn: 298737

1 files changed, 21 insertions, 9 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIAnnotateControlFlow.cpp b/llvm/lib/Target/AMDGPU/SIAnnotateControlFlow.cpp
index c9834bf5364..b7e62075244 100644
--- a/llvm/lib/Target/AMDGPU/SIAnnotateControlFlow.cpp
+++ b/llvm/lib/Target/AMDGPU/SIAnnotateControlFlow.cpp
@@ -22,6 +22,7 @@
 #include "llvm/IR/Module.h"
 #include "llvm/Pass.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/SSAUpdater.h"
 
 using namespace llvm;
@@ -77,7 +78,8 @@ class SIAnnotateControlFlow : public FunctionPass {
   void insertElse(BranchInst *Term);
 
   Value *handleLoopCondition(Value *Cond, PHINode *Broken,
-                             llvm::Loop *L, BranchInst *Term);
+                             llvm::Loop *L, BranchInst *Term,
+                             SmallVectorImpl<WeakVH> &LoopPhiConditions);
 
   void handleLoop(BranchInst *Term);
 
@@ -183,8 +185,9 @@ bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
 
 // \brief Erase "Phi" if it is not used any more
 void SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
-  if (!Phi->hasNUsesOrMore(1))
-    Phi->eraseFromParent();
+  if (llvm::RecursivelyDeleteDeadPHINode(Phi)) {
+    DEBUG(dbgs() << "Erased unused condition phi\n");
+  }
 }
 
 /// \brief Open a new "If" block
@@ -208,8 +211,10 @@ void SIAnnotateControlFlow::insertElse(BranchInst *Term) {
 }
 
 /// \brief Recursively handle the condition leading to a loop
-Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken,
-                                             llvm::Loop *L, BranchInst *Term) {
+Value *SIAnnotateControlFlow::handleLoopCondition(
+  Value *Cond, PHINode *Broken,
+  llvm::Loop *L, BranchInst *Term,
+  SmallVectorImpl<WeakVH> &LoopPhiConditions) {
 
   // Only search through PHI nodes which are inside the loop.  If we try this
   // with PHI nodes that are outside of the loop, we end up inserting new PHI
@@ -233,14 +238,14 @@ Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken,
       }
 
       Phi->setIncomingValue(i, BoolFalse);
-      Value *PhiArg = handleLoopCondition(Incoming, Broken, L, Term);
+      Value *PhiArg = handleLoopCondition(Incoming, Broken, L,
+                                          Term, LoopPhiConditions);
       NewPhi->addIncoming(PhiArg, From);
     }
 
     BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();
 
     for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
-
       Value *Incoming = Phi->getIncomingValue(i);
       if (Incoming != BoolTrue)
         continue;
@@ -276,7 +281,7 @@ Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken,
       NewPhi->setIncomingValue(i, PhiArg);
     }
 
-    eraseIfUnused(Phi);
+    LoopPhiConditions.push_back(WeakVH(Phi));
     return Ret;
   }
 
@@ -318,14 +323,21 @@ void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
   BasicBlock *Target = Term->getSuccessor(1);
   PHINode *Broken = PHINode::Create(Int64, 0, "phi.broken", &Target->front());
 
+  SmallVector<WeakVH, 8> LoopPhiConditions;
   Value *Cond = Term->getCondition();
   Term->setCondition(BoolTrue);
-  Value *Arg = handleLoopCondition(Cond, Broken, L, Term);
+  Value *Arg = handleLoopCondition(Cond, Broken, L, Term, LoopPhiConditions);
 
   for (BasicBlock *Pred : predecessors(Target))
     Broken->addIncoming(Pred == BB ? Arg : Int64Zero, Pred);
 
   Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
+
+  for (WeakVH Val : reverse(LoopPhiConditions)) {
+    if (PHINode *Cond = cast_or_null<PHINode>(Val))
+      eraseIfUnused(Cond);
+  }
+
   push(Term->getSuccessor(0), Arg);
 }