AliasSetTracker: UnknownInsts should contribute to the refcount

AliasSetTracker::addUnknown may create an AliasSet devoid of pointers
just to contain an instruction if no suitable AliasSet already exists.
It will then AliasSet::addUnknownInst and we will be done.

However, it's possible for addUnknown to choose an existing AliasSet to
addUnknownInst.
If this were to occur, we are in a bit of a pickle: removing pointers
from the AliasSet can cause the entire AliasSet to become destroyed,
taking our unknown instructions out with them.

Instead, keep track whether or not our AliasSet has any unknown
instructions.

This fixes PR21582.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222338 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Analysis/AliasSetTracker.h b/include/llvm/Analysis/AliasSetTracker.h
index 403a2b586f689f4219d82ee315d8bd0ec1bb414b..036d58dfa8108af507092558f33aadeb1f0b947e 100644 (file)
--- a/include/llvm/Analysis/AliasSetTracker.h
+++ b/include/llvm/Analysis/AliasSetTracker.h
@@ -254,13 +254,16 @@ private:
                   const AAMDNodes &AAInfo,
                   bool KnownMustAlias = false);
   void addUnknownInst(Instruction *I, AliasAnalysis &AA);
-  void removeUnknownInst(Instruction *I) {
+  void removeUnknownInst(AliasSetTracker &AST, Instruction *I) {
+    bool WasEmpty = UnknownInsts.empty();
     for (size_t i = 0, e = UnknownInsts.size(); i != e; ++i)
       if (UnknownInsts[i] == I) {
         UnknownInsts[i] = UnknownInsts.back();
         UnknownInsts.pop_back();
         --i; --e;  // Revisit the moved entry.
       }
+    if (!WasEmpty && UnknownInsts.empty())
+      dropRef(AST);
   }
   void setVolatile() { Volatile = true; }
 

diff --git a/lib/Analysis/AliasSetTracker.cpp b/lib/Analysis/AliasSetTracker.cpp
index 9d941e557978c6183e4b7f5e14496c102ad99976..5b85f65d44257e5d013be77b7189cca5a59c6e2f 100644 (file)
--- a/lib/Analysis/AliasSetTracker.cpp
+++ b/lib/Analysis/AliasSetTracker.cpp
@@ -55,12 +55,16 @@ void AliasSet::mergeSetIn(AliasSet &AS, AliasSetTracker &AST) {
       AliasTy = MayAlias;
   }
 
+  bool ASHadUnknownInsts = false;
   if (UnknownInsts.empty()) {            // Merge call sites...
-    if (!AS.UnknownInsts.empty())
+    if (!AS.UnknownInsts.empty()) {
       std::swap(UnknownInsts, AS.UnknownInsts);
+      addRef();
+    }
   } else if (!AS.UnknownInsts.empty()) {
     UnknownInsts.insert(UnknownInsts.end(), AS.UnknownInsts.begin(), AS.UnknownInsts.end());
     AS.UnknownInsts.clear();
+    ASHadUnknownInsts = true;
   }
 
   AS.Forward = this;  // Forward across AS now...
@@ -76,6 +80,8 @@ void AliasSet::mergeSetIn(AliasSet &AS, AliasSetTracker &AST) {
     AS.PtrListEnd = &AS.PtrList;
     assert(*AS.PtrListEnd == nullptr && "End of list is not null?");
   }
+  if (ASHadUnknownInsts)
+    AS.dropRef(AST);
 }
 
 void AliasSetTracker::removeAliasSet(AliasSet *AS) {
@@ -123,6 +129,8 @@ void AliasSet::addPointer(AliasSetTracker &AST, PointerRec &Entry,
 }
 
 void AliasSet::addUnknownInst(Instruction *I, AliasAnalysis &AA) {
+  if (UnknownInsts.empty())
+    addRef();
   UnknownInsts.push_back(I);
 
   if (!I->mayWriteToMemory()) {
@@ -218,13 +226,14 @@ AliasSet *AliasSetTracker::findAliasSetForPointer(const Value *Ptr,
                                                   uint64_t Size,
                                                   const AAMDNodes &AAInfo) {
   AliasSet *FoundSet = nullptr;
-  for (iterator I = begin(), E = end(); I != E; ++I) {
-    if (I->Forward || !I->aliasesPointer(Ptr, Size, AAInfo, AA)) continue;
+  for (iterator I = begin(), E = end(); I != E;) {
+    iterator Cur = I++;
+    if (Cur->Forward || !Cur->aliasesPointer(Ptr, Size, AAInfo, AA)) continue;
     
     if (!FoundSet) {      // If this is the first alias set ptr can go into.
-      FoundSet = I;       // Remember it.
+      FoundSet = Cur;     // Remember it.
     } else {              // Otherwise, we must merge the sets.
-      FoundSet->mergeSetIn(*I, *this);     // Merge in contents.
+      FoundSet->mergeSetIn(*Cur, *this);     // Merge in contents.
     }
   }
 
@@ -251,14 +260,14 @@ bool AliasSetTracker::containsUnknown(Instruction *Inst) const {
 
 AliasSet *AliasSetTracker::findAliasSetForUnknownInst(Instruction *Inst) {
   AliasSet *FoundSet = nullptr;
-  for (iterator I = begin(), E = end(); I != E; ++I) {
-    if (I->Forward || !I->aliasesUnknownInst(Inst, AA))
+  for (iterator I = begin(), E = end(); I != E;) {
+    iterator Cur = I++;
+    if (Cur->Forward || !Cur->aliasesUnknownInst(Inst, AA))
       continue;
-    
     if (!FoundSet)            // If this is the first alias set ptr can go into.
-      FoundSet = I;           // Remember it.
-    else if (!I->Forward)     // Otherwise, we must merge the sets.
-      FoundSet->mergeSetIn(*I, *this);     // Merge in contents.
+      FoundSet = Cur;         // Remember it.
+    else if (!Cur->Forward)   // Otherwise, we must merge the sets.
+      FoundSet->mergeSetIn(*Cur, *this);     // Merge in contents.
   }
   return FoundSet;
 }
@@ -406,6 +415,8 @@ void AliasSetTracker::add(const AliasSetTracker &AST) {
 /// tracker.
 void AliasSetTracker::remove(AliasSet &AS) {
   // Drop all call sites.
+  if (!AS.UnknownInsts.empty())
+    AS.dropRef(*this);
   AS.UnknownInsts.clear();
   
   // Clear the alias set.
@@ -510,10 +521,10 @@ void AliasSetTracker::deleteValue(Value *PtrVal) {
   if (Instruction *Inst = dyn_cast<Instruction>(PtrVal)) {
     if (Inst->mayReadOrWriteMemory()) {
       // Scan all the alias sets to see if this call site is contained.
-      for (iterator I = begin(), E = end(); I != E; ++I) {
-        if (I->Forward) continue;
-        
-        I->removeUnknownInst(Inst);
+      for (iterator I = begin(), E = end(); I != E;) {
+        iterator Cur = I++;
+        if (!Cur->Forward)
+          Cur->removeUnknownInst(*this, Inst);
       }
     }
   }

diff --git a/test/Transforms/LICM/PR21582.ll b/test/Transforms/LICM/PR21582.ll
new file mode 100644 (file)
index 0000000..c068c2f
--- /dev/null
+++ b/test/Transforms/LICM/PR21582.ll
@@ -0,0 +1,40 @@
+; RUN: opt < %s -basicaa -licm -S | FileCheck %s
+@b = external global i32, align 4
+@fn3.i = external global i32, align 4
+
+declare i32 @g() nounwind
+
+define i32 @f() {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.end, %entry
+; CHECK-LABEL: for.cond:
+; CHECK: store i32 0, i32* @b
+  store i32 0, i32* @b, align 4
+  br i1 true, label %for.body.preheader, label %for.end
+
+for.body.preheader:                               ; preds = %for.cond
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %for.body.preheader
+  %g.15 = phi i32 [ undef, %for.body ], [ 0, %for.body.preheader ]
+  %arrayidx2 = getelementptr inbounds i32* @fn3.i, i64 0
+  %0 = load i32* %arrayidx2, align 4
+  %call = call i32 @g()
+  br i1 false, label %for.body, label %for.end.loopexit
+
+for.end.loopexit:                                 ; preds = %for.body
+  br label %for.end
+
+for.end:                                          ; preds = %for.end.loopexit, %for.cond
+  %whatever = phi i32 [ %call, %for.end.loopexit ], [ undef, %for.cond ]
+  br i1 false, label %for.cond, label %if.then
+
+if.then:                                          ; preds = %for.end
+; CHECK-LABEL: if.then:
+; CHECK: phi i32 [ {{.*}}, %for.end ]
+; CHECK-NOT: store i32 0, i32* @b
+; CHECK: ret i32
+  ret i32 %whatever
+}