6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-07-24 22:24:54 +00:00
Code Issues Projects Releases Wiki Activity

[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.

Browse Source 
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
This commit is contained in:
Michael Gottesman
2013-04-18 05:39:45 +00:00
parent 8a709208ed
commit 0556900b26
2 changed files with 167 additions and 96 deletions
Download Patch File Download Diff File Expand all files Collapse all files

36
test/Transforms/ObjCARC/cfg-hazards.ll
View File

@@ -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 !{}