[11u]RFR[S]:8240715: fail to build with gcc 6.3.1 [-Werror=maybe-uninitialized](Internet mail)

[linzang(臧琳)]

Hi David, Christph, 
   I can not reproduce this issue with same gcc on Jdk/jdk. 
   So I  asked should this issue be fixed or not.
   It also makes wondering why jdk/jdk could pass build with same gcc 6.3.1 
   So if it was dicided not to fix, I will close the issue. 

BRs,
Lin

On 2020/3/9, 5:20 PM, "David Holmes" <david.holmes at oracle.com> wrote:

    They look like false-positives flagged by gcc 6.3.1. IIRC these are not 
    flagged in later gcc versions and it was decided not to "fix" them.
    
    David
    
    On 9/03/2020 7:15 pm, Langer, Christoph wrote:
    > Hi Lin,
    > 
    > I compared the coding that you touch to the current versions in head and the code there seems quite the same or at least similar in regards to the possible warnings.
    > 
    > I rather suggest you do the change in jdk/jdk first and we'd then backport it? Or is there anything which speaks against doing this in head?
    > 
    > Cheers
    > Christoph
    > 
    > 
    > -----Original Message-----
    > From: jdk-updates-dev <jdk-updates-dev-bounces at openjdk.java.net> On Behalf Of linzang(??)
    > Sent: Sonntag, 8. März 2020 09:23
    > To: jdk-updates-dev at openjdk.java.net
    > Subject: Re: [11u]RFR[S]:8240715: fail to build with gcc 6.3.1 [-Werror=maybe-uninitialized]
    > 
    > I made a tiny patch for this:
    > Please help to review.
    > Webrev: http://cr.openjdk.java.net/~lzang/11u/JDK-8240715/webrev/
    > Bug: https://bugs.openjdk.java.net/browse/JDK-8240715
    > 
    > 
    > BRs,
    > Lin
    > 
    > From: "linzang(臧琳)" <linzang at tencent.com>
    > Date: Saturday, March 7, 2020 at 12:33 AM
    > To: "jdk-updates-dev at openjdk.java.net" <jdk-updates-dev at openjdk.java.net>
    > Subject: [11u] fail to build with gcc 6.3.1 [-Werror=maybe-uninitialized]
    > 
    > Hi,
    >       The 11u-dev repo fail to build with gcc 6.3.1, error message:
    > ====================================================
    >          In file included from / Source/jdk11u-dev/src/hotspot/cpu/x86/assembler_x86.inline.hpp:30:0,
    >                   from / Source/jdk11u-dev/src/hotspot/share/asm/assembler.inline.hpp:30,
    >                   from / Source/jdk11u-dev/src/hotspot/share/precompiled/precompiled.hpp:32:
    > /Source/jdk11u-dev/src/hotspot/share/code/codeCache.hpp: In member function 'void G1CollectedHeap::complete_cleaning(BoolObjectClosure*, bool)':
    > /Source/jdk11u-dev/src/hotspot/share/code/codeCache.hpp:377:5: error: 'iter.CodeBlobIterator<CompiledMethod, CompiledMethodFilter>::_code_blob' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    >       if (_code_blob == NULL) {
    >       ^~
    > /Source/jdk11u-dev/src/hotspot/share/gc/g1/g1CollectedHeap.cpp:3355:28: note: 'iter.CodeBlobIterator<CompiledMethod, CompiledMethodFilter>::_code_blob' was declared here
    >       CompiledMethodIterator iter = CompiledMethodIterator();
    >                              ^~~~
    > cc1plus: all warnings being treated as errors
    > 
    > The build can success with –disable-warnings-as-errors  or with simple change:
    > diff -r e5802f7424cf src/hotspot/share/code/codeCache.hpp
    > --- a/src/hotspot/share/code/codeCache.hpp      Fri May 24 13:52:33 2019 -0700
    > +++ b/src/hotspot/share/code/codeCache.hpp      Fri Mar 06 15:00:55 2020 +0800
    > @@ -322,6 +322,7 @@
    >    public:
    >     CodeBlobIterator(T* nm = NULL) {
    > +    _code_blob = NULL;
    >       if (Filter::heaps() == NULL) {
    >         return;
    >       }
    > diff -r e5802f7424cf src/hotspot/share/gc/shared/genCollectedHeap.cpp
    > --- a/src/hotspot/share/gc/shared/genCollectedHeap.cpp  Fri May 24 13:52:33 2019 -0700
    > +++ b/src/hotspot/share/gc/shared/genCollectedHeap.cpp  Fri Mar 06 15:00:55 2020 +0800
    > @@ -1146,6 +1146,7 @@
    >     size_t min_size = 0;   // "first" makes this conceptually infinite.
    >     ScratchBlock **smallest_ptr, *smallest;
    >     ScratchBlock  *cur = *prev_ptr;
    > +  smallest_ptr = NULL;
    >     while (cur) {
    >       assert(*prev_ptr == cur, "just checking");
    >       if (first || cur->num_words < min_size) {
    > -----------------------------------------------------------
    > 
    > So could this be a fix ?
    > 
    > BRs,
    > Lin
    >