Suppress partial retain+release elimination when there's a

possibility that it will span multiple CFG diamonds/triangles which
could have different controlling predicates.  rdar://10282956


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142222 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/ObjCARC.cpp

@@ -1158,6 +1158,11 @@ namespace {
     /// with the "tail" keyword.
     bool IsTailCallRelease;
 
+    /// Partial - True of we've seen an opportunity for partial RR elimination,
+    /// such as pushing calls into a CFG triangle or into one side of a
+    /// CFG diamond.
+    bool Partial;
+
     /// ReleaseMetadata - If the Calls are objc_release calls and they all have
     /// a clang.imprecise_release tag, this is the metadata tag.
     MDNode *ReleaseMetadata;
@@ -1172,6 +1177,7 @@ namespace {
 
     RRInfo() :
       KnownSafe(false), IsRetainBlock(false), IsTailCallRelease(false),
+      Partial(false),
       ReleaseMetadata(0) {}
 
     void clear();
@@ -1182,6 +1188,7 @@ void RRInfo::clear() {
   KnownSafe = false;
   IsRetainBlock = false;
   IsTailCallRelease = false;
+  Partial = false;
   ReleaseMetadata = 0;
   Calls.clear();
   ReverseInsertPts.clear();
@@ -1272,8 +1279,16 @@ PtrState::Merge(const PtrState &Other, bool TopDown) {
   if (RRI.IsRetainBlock != Other.RRI.IsRetainBlock)
     Seq = S_None;
 
+  // If we're not in a sequence (anymore), drop all associated state.
   if (Seq == S_None) {
     RRI.clear();
+  } else if (RRI.Partial || Other.RRI.Partial) {
+    // If we're doing a merge on a path that's previously seen a partial
+    // merge, conservatively drop the sequence, to avoid doing partial
+    // RR elimination. If the branch predicates for the two merge differ,
+    // mixing them is unsafe.
+    Seq = S_None;
+    RRI.clear();
   } else {
     // Conservatively merge the ReleaseMetadata information.
     if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata)
@@ -1282,8 +1297,15 @@ PtrState::Merge(const PtrState &Other, bool TopDown) {
     RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe;
     RRI.IsTailCallRelease = RRI.IsTailCallRelease && Other.RRI.IsTailCallRelease;
     RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end());
-    RRI.ReverseInsertPts.insert(Other.RRI.ReverseInsertPts.begin(),
+
-                                Other.RRI.ReverseInsertPts.end());
+    // Merge the insert point sets. If there are any differences,
+    // that makes this a partial merge.
+    RRI.Partial = RRI.ReverseInsertPts.size() !=
+                  Other.RRI.ReverseInsertPts.size();
+    for (SmallPtrSet<Instruction *, 2>::const_iterator
+         I = Other.RRI.ReverseInsertPts.begin(),
+         E = Other.RRI.ReverseInsertPts.end(); I != E; ++I)
+      RRI.Partial |= RRI.ReverseInsertPts.insert(*I);
   }
 }
 

test/Transforms/ObjCARC/basic.ll

@@ -86,6 +86,37 @@ alt_return:
   ret void
 }
 
+; Don't do partial elimination into two different CFG diamonds.
+
+; CHECK: define void @test1b(
+; CHECK: entry:
+; CHECK:   tail call i8* @objc_retain(i8* %x) nounwind
+; CHECK-NOT: @objc_
+; CHECK: if.end5:
+; CHECK:   tail call void @objc_release(i8* %x) nounwind, !clang.imprecise_release !0
+; CHECK-NOT: @objc_
+; CHECK: }
+define void @test1b(i8* %x, i1 %p, i1 %q) {
+entry:
+  tail call i8* @objc_retain(i8* %x) nounwind
+  br i1 %p, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  tail call void @callee()
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %entry
+  br i1 %q, label %if.then3, label %if.end5
+
+if.then3:                                         ; preds = %if.end
+  tail call void @use_pointer(i8* %x)
+  br label %if.end5
+
+if.end5:                                          ; preds = %if.then3, %if.end
+  tail call void @objc_release(i8* %x) nounwind, !clang.imprecise_release !0
+  ret void
+}
+
 ; Like test0 but the pointer is passed to an intervening call,
 ; so the optimization is not safe.