• David Chase's avatar
    cmd/compile: ignore OXXX nodes in closure captured vars list · b64f549b
    David Chase authored
    Added a debug flag "-d closure" to explain compilation of
    closures (should this be done some other way? Should we
    rewrite the "-m" flag to "-d escapes"?)  Used this to
    discover that cause was an OXXX node in the captured vars
    list, and in turn noticed that OXXX nodes are explicitly
    ignored in all other processing of captured variables.
    
    Couldn't figure out a reproducer, did verify that this OXXX
    was not caused by an unnamed return value (which is one use
    of these).  Verified lack of heap allocation by examining -S
    output.
    
    Assembly:
    (runtime/mgc.go:1371) PCDATA $0, $2
    (runtime/mgc.go:1371) CALL "".notewakeup(SB)
    (runtime/mgc.go:1377) LEAQ "".gcBgMarkWorker.func1·f(SB), AX
    (runtime/mgc.go:1404) MOVQ AX, (SP)
    (runtime/mgc.go:1404) MOVQ "".autotmp_2242+88(SP), CX
    (runtime/mgc.go:1404) MOVQ CX, 8(SP)
    (runtime/mgc.go:1404) LEAQ go.string."GC worker (idle)"(SB), AX
    (runtime/mgc.go:1404) MOVQ AX, 16(SP)
    (runtime/mgc.go:1404) MOVQ $16, 24(SP)
    (runtime/mgc.go:1404) MOVB $20, 32(SP)
    (runtime/mgc.go:1404) MOVQ $0, 40(SP)
    (runtime/mgc.go:1404) PCDATA $0, $2
    (runtime/mgc.go:1404) CALL "".gopark(SB)
    
    Added a check for compiling_runtime to ensure that this is
    caught in the future.  Added a test to test the check.
    Verified that 1.5.3 did NOT reject the test case when
    compiled with -+ flag, so this is not a recently added bug.
    
    Cause of bug is two-part -- there was no leaking closure
    detection ever, and instead it relied on capture-of-variables
    to trigger compiling_runtime test, but closures improved in
    1.5.3 so that mere capture of a value did not also capture
    the variable, which thus allowed closures to escape, as well
    as this case where the escape was spurious.  In
    fixedbugs/issue14999.go, compare messages for f and g;
    1.5.3 would reject g, but not f.  1.4 rejects both because
    1.4 heap-allocates parameter x for both.
    
    Fixes #14999.
    
    Change-Id: I40bcdd27056810628e96763a44f2acddd503aee1
    Reviewed-on: https://go-review.googlesource.com/21322
    Run-TryBot: David Chase <drchase@google.com>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: 's avatarKeith Randall <khr@golang.org>
    b64f549b
issue14999.go 521 Bytes