[objc-arc] Do not mismatch up retains inside a for loop with releases outside said for loop in the presense of differing provenance caused by escaping blocks.

This occurs due to an alloca representing a separate ownership from the
original pointer. Thus consider the following pseudo-IR:

  objc_retain(%a)
  for (...) {
    objc_retain(%a)
    %block <- %a
    F(%block)
    objc_release(%block)
  }
  objc_release(%a)

From the perspective of the optimizer, the %block is a separate
provenance from the original %a. Thus the optimizer pairs up the inner
retain for %a and the outer release from %a, resulting in segfaults.

This is fixed by noting that the signature of a mismatch of
retain/releases inside the for loop is a Use/CanRelease top down with an
None bottom up (since bottom up the Retain-CanRelease-Use-Release
sequence is completed by the inner objc_retain, but top down due to the
differing provenance from the objc_release said sequence is not
completed). In said case in CheckForCFGHazards, we now clear the state
of %a implying that no pairing will occur.

Additionally a test case is included.

rdar://12969722

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179747 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 36 insertions, 0 deletions

diff --git a/test/Transforms/ObjCARC/cfg-hazards.ll b/test/Transforms/ObjCARC/cfg-hazards.ll
index 899298b596..0156d5bfb4 100644
--- a/test/Transforms/ObjCARC/cfg-hazards.ll
+++ b/test/Transforms/ObjCARC/cfg-hazards.ll
@@ -8,6 +8,7 @@ declare void @use_pointer(i8*)
 declare i8* @objc_retain(i8*)
 declare void @objc_release(i8*)
 declare void @callee()
+declare void @block_callee(void ()*)
 
 ; CHECK: define void @test0(
 ; CHECK:   call i8* @objc_retain(
@@ -394,6 +395,41 @@ exit:
   ret void
 }
 
+; Do not improperly pair retains in a for loop with releases outside of a for
+; loop when the proper pairing is disguised by a separate provenance represented
+; by an alloca.
+; rdar://12969722
+
+; CHECK: define void @test13(i8* %a) [[NUW]] {
+; CHECK: entry:
+; CHECK:   tail call i8* @objc_retain(i8* %a) [[NUW]]
+; CHECK: loop:
+; CHECK:   tail call i8* @objc_retain(i8* %a) [[NUW]]
+; CHECK:   call void @block_callee
+; CHECK:   call void @objc_release(i8* %reloaded_a) [[NUW]]
+; CHECK: exit:
+; CHECK:   call void @objc_release(i8* %a) [[NUW]]
+; CHECK: }
+define void @test13(i8* %a) nounwind {
+entry:
+  %block = alloca i8*
+  %a1 = tail call i8* @objc_retain(i8* %a) nounwind
+  br label %loop
+
+loop:
+  %a2 = tail call i8* @objc_retain(i8* %a) nounwind
+  store i8* %a, i8** %block, align 8
+  %casted_block = bitcast i8** %block to void ()*
+  call void @block_callee(void ()* %casted_block)
+  %reloaded_a = load i8** %block, align 8
+  call void @objc_release(i8* %reloaded_a) nounwind, !clang.imprecise_release !0
+  br i1 undef, label %loop, label %exit
+  
+exit:
+  call void @objc_release(i8* %a) nounwind, !clang.imprecise_release !0
+  ret void
+}
+
 ; CHECK: attributes [[NUW]] = { nounwind }
 
 !0 = metadata !{}