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[ObjC][ARC] Don't move a retain call living outside a loop into the loop

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We started seeing cases where ARC optimizer would move retain calls into
loop bodies, causing imbalance in the number of retain and release
calls, after changes were made to delete inert ARC calls since the inert
calls that used to block code motion are gone.

Fix the bug by setting the CFG hazard flag when visiting a loop header.

rdar://problem/56908836
This commit is contained in:
Akira Hatanaka 2020-02-25 12:20:07 -08:00
parent 6f1baa331b
commit 7959a50eda
2 changed files with 51 additions and 0 deletions
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9
lib/Transforms/ObjCARC/ObjCARCOpts.cpp
View File

@ -1569,6 +1569,15 @@ ObjCARCOpt::VisitTopDown(BasicBlock *BB,
}
}
// Check that BB and MyStates have the same number of predecessors. This
// prevents retain calls that live outside a loop from being moved into the
// loop.
if (!BB->hasNPredecessors(MyStates.pred_end() - MyStates.pred_begin()))
for (auto I = MyStates.top_down_ptr_begin(),
E = MyStates.top_down_ptr_end();
I != E; ++I)
I->second.SetCFGHazardAfflicted(true);
LLVM_DEBUG(dbgs() << "Before:\n"
<< BBStates[BB] << "\n"
<< "Performing Dataflow:\n");

42
test/Transforms/ObjCARC/cfg-hazards.ll
View File

@ -430,6 +430,48 @@ exit:
ret void
}
; The retain call in the entry block shouldn't be moved to the loop body.
; CHECK: define void @test14(i8* %[[VAL0:.*]],
; CHECK: %[[V1:.*]] = tail call i8* @llvm.objc.retain(i8* %[[VAL0]])
; CHECK: %[[CMP:.*]] = icmp eq i8* %[[VAL0]], null
; CHECK: br i1 %[[CMP]], label %{{.*}}, label %{{.*}}
define void @test14(i8* %val0, i8 %val1) {
entry:
%v1 = tail call i8* @llvm.objc.retain(i8* %val0)
%cmp = icmp eq i8* %val0, null
br i1 %cmp, label %if.end27, label %if.then
if.then:
%tobool = icmp eq i8 %val1, 1
br label %for.body
for.cond:
%cmp6 = icmp eq i8 %val1, 2
br i1 %cmp6, label %for.body, label %for.end.loopexit
for.body:
call void @callee()
%tobool9 = icmp eq i8 %val1, 0
br i1 %tobool9, label %for.cond, label %if.then10
if.then10:
br label %for.end
for.end.loopexit:
br label %for.end
for.end:
call void @callee()
call void @use_pointer(i8* %v1)
br label %if.end27
if.end27:
call void @llvm.objc.release(i8* %v1) #0, !clang.imprecise_release !0
ret void
}
; CHECK: attributes [[NUW]] = { nounwind }
!0 = !{}