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Avoid some new gcc warnings in 15 #10808

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merged 2 commits into from
Jul 15, 2017
Merged

Avoid some new gcc warnings in 15 #10808

merged 2 commits into from
Jul 15, 2017

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TheBlueMatt
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This, plus #10714 avoids adding new compile-time warnings in 15.

Fixes a warning added in #10792.

gmaxwell
gmaxwell approved these changes Jul 12, 2017
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utACK

@meshcollider
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utACK

@achow101
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utACK a8a602e

sipa
sipa reviewed Jul 13, 2017
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src/prevector.h Outdated
prevector() : _size(0) {}
prevector() : _size(0) {
// Explicitly initialize indirect ptr to avoid "used uninitialized" warning
_union.indirect = nullptr;
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I was vaguely concerned that this assignment violates type punning through a union, but (1) some sources say that is permitted anyway (2) the other type is char (for which exceptions to type punning exist) and (3) we'll write to the union again before ever using data in it.

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I though type-punning through an union was the only acceptable way to do it?

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From IRC:
sipa: why not use aggregate initialization: prevector() : _size(0), _union{{}}
or give the union a ctor?

I can't reproduce the warning, so I can't be sure that it satisfies whatever compiler is complaining, but the above compiles fine for me, and I'd think that initializing via a ctor would work otherwise.

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@laanwj There is a faction of language wonks/compiler folks that argues that it is never acceptable (except with char) per the language specs; -- and I believe there is nothing in any of the C++ standards that make it clear that its kosher (though sipa tells me apparently C11 has something explicit). Since having no way to do it is not a very realistic position it doesn't reflect the behavior of compilers today. Generally better to avoid it at least where its convenient, or at least be aware that someday it might become non-kosher depending on which evil spirits control the souls of the compiler authors next week. :)

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I'm super not convinced this is an issue. If we're really concerned, easiest fix is probably require C11 and turn prevector into C++ wrapper around C. More realistically, gcc explicitly supports this, and I believe many other compilers as well.

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sipa commented Jul 13, 2017

utACK

@paveljanik
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ACK

Please fix typo in the second commit message (initizlie).

@fanquake fanquake mentioned this pull request Jul 13, 2017
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sipa commented Jul 14, 2017 •
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@theuni's suggestion looks the cleanest to me. Would you mind trying that?

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OK, took @theuni's version (which has no warnings for me).

@TheBlueMatt
Explicitly initialize prevector::_union to avoid new warning
c73b8be 
Warning from gcc 7.1 is ./prevector.h:450:25: warning:
'*((void*)(&<anonymous>)+8).prevector<28, unsigned char>::_union.prevector<28, unsigned char>::direct_or_indirect::<anonymous>.prevector<28, unsigned char>::direct_or_indirect::<unnamed struct>::indirect'
may be used uninitialized in this function [-Wmaybe-uninitialized]
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sipa commented Jul 15, 2017

utACK c73b8be

@sipa sipa merged commit c73b8be into bitcoin:master Jul 15, 2017
sipa added a commit that referenced this pull request Jul 15, 2017
@sipa
Merge #10808: Avoid some new gcc warnings in 15
ec8a50b 
c73b8be Explicitly initialize prevector::_union to avoid new warning (Matt Corallo)
1016dac Fix signed/unsigned comparison warning introduced in c8e29d7. (Matt Corallo)

Tree-SHA512: d1574b0fdc9bfddc3517c382d34418b1d8ed80c81d2f6fd19378c064af8d7704fb84ef8b740ff97f7ec7609bd6de76348921fcc227e1ce97127947a0d22c7887
PastaPastaPasta pushed a commit to PastaPastaPasta/dash that referenced this pull request Jul 6, 2019
@sipa @PastaPastaPasta
Merge bitcoin#10808: Avoid some new gcc warnings in 15
a49d864 
c73b8be Explicitly initialize prevector::_union to avoid new warning (Matt Corallo)
1016dac Fix signed/unsigned comparison warning introduced in c8e29d7. (Matt Corallo)

Tree-SHA512: d1574b0fdc9bfddc3517c382d34418b1d8ed80c81d2f6fd19378c064af8d7704fb84ef8b740ff97f7ec7609bd6de76348921fcc227e1ce97127947a0d22c7887
PastaPastaPasta pushed a commit to PastaPastaPasta/dash that referenced this pull request Jul 8, 2019
@sipa @PastaPastaPasta
Merge bitcoin#10808: Avoid some new gcc warnings in 15
790aa75 
c73b8be Explicitly initialize prevector::_union to avoid new warning (Matt Corallo)
1016dac Fix signed/unsigned comparison warning introduced in c8e29d7. (Matt Corallo)

Tree-SHA512: d1574b0fdc9bfddc3517c382d34418b1d8ed80c81d2f6fd19378c064af8d7704fb84ef8b740ff97f7ec7609bd6de76348921fcc227e1ce97127947a0d22c7887
PastaPastaPasta pushed a commit to PastaPastaPasta/dash that referenced this pull request Jul 9, 2019
@sipa @PastaPastaPasta
Merge bitcoin#10808: Avoid some new gcc warnings in 15
e12f8f4 
c73b8be Explicitly initialize prevector::_union to avoid new warning (Matt Corallo)
1016dac Fix signed/unsigned comparison warning introduced in c8e29d7. (Matt Corallo)

Tree-SHA512: d1574b0fdc9bfddc3517c382d34418b1d8ed80c81d2f6fd19378c064af8d7704fb84ef8b740ff97f7ec7609bd6de76348921fcc227e1ce97127947a0d22c7887
PastaPastaPasta pushed a commit to PastaPastaPasta/dash that referenced this pull request Jul 11, 2019
@sipa @PastaPastaPasta
Merge bitcoin#10808: Avoid some new gcc warnings in 15
5b1e542 
c73b8be Explicitly initialize prevector::_union to avoid new warning (Matt Corallo)
1016dac Fix signed/unsigned comparison warning introduced in c8e29d7. (Matt Corallo)

Tree-SHA512: d1574b0fdc9bfddc3517c382d34418b1d8ed80c81d2f6fd19378c064af8d7704fb84ef8b740ff97f7ec7609bd6de76348921fcc227e1ce97127947a0d22c7887
PastaPastaPasta pushed a commit to PastaPastaPasta/dash that referenced this pull request Jul 13, 2019
@sipa @PastaPastaPasta
Merge bitcoin#10808: Avoid some new gcc warnings in 15
68ac274 
c73b8be Explicitly initialize prevector::_union to avoid new warning (Matt Corallo)
1016dac Fix signed/unsigned comparison warning introduced in c8e29d7. (Matt Corallo)

Tree-SHA512: d1574b0fdc9bfddc3517c382d34418b1d8ed80c81d2f6fd19378c064af8d7704fb84ef8b740ff97f7ec7609bd6de76348921fcc227e1ce97127947a0d22c7887
PastaPastaPasta pushed a commit to PastaPastaPasta/dash that referenced this pull request Jul 17, 2019
@sipa @PastaPastaPasta
Merge bitcoin#10808: Avoid some new gcc warnings in 15
ac6162a 
c73b8be Explicitly initialize prevector::_union to avoid new warning (Matt Corallo)
1016dac Fix signed/unsigned comparison warning introduced in c8e29d7. (Matt Corallo)

Tree-SHA512: d1574b0fdc9bfddc3517c382d34418b1d8ed80c81d2f6fd19378c064af8d7704fb84ef8b740ff97f7ec7609bd6de76348921fcc227e1ce97127947a0d22c7887
PastaPastaPasta pushed a commit to PastaPastaPasta/dash that referenced this pull request Jul 17, 2019
@sipa @PastaPastaPasta
Merge bitcoin#10808: Avoid some new gcc warnings in 15
354b75f 
c73b8be Explicitly initialize prevector::_union to avoid new warning (Matt Corallo)
1016dac Fix signed/unsigned comparison warning introduced in c8e29d7. (Matt Corallo)

Tree-SHA512: d1574b0fdc9bfddc3517c382d34418b1d8ed80c81d2f6fd19378c064af8d7704fb84ef8b740ff97f7ec7609bd6de76348921fcc227e1ce97127947a0d22c7887
PastaPastaPasta pushed a commit to PastaPastaPasta/dash that referenced this pull request Jul 18, 2019
@sipa @PastaPastaPasta
Merge bitcoin#10808: Avoid some new gcc warnings in 15
29760e7 
c73b8be Explicitly initialize prevector::_union to avoid new warning (Matt Corallo)
1016dac Fix signed/unsigned comparison warning introduced in c8e29d7. (Matt Corallo)

Tree-SHA512: d1574b0fdc9bfddc3517c382d34418b1d8ed80c81d2f6fd19378c064af8d7704fb84ef8b740ff97f7ec7609bd6de76348921fcc227e1ce97127947a0d22c7887
barrystyle pushed a commit to PACGlobalOfficial/PAC that referenced this pull request Jan 22, 2020
@sipa @barrystyle
Merge bitcoin#10808: Avoid some new gcc warnings in 15
8ab4cfa 
c73b8be Explicitly initialize prevector::_union to avoid new warning (Matt Corallo)
1016dac Fix signed/unsigned comparison warning introduced in c8e29d7. (Matt Corallo)

Tree-SHA512: d1574b0fdc9bfddc3517c382d34418b1d8ed80c81d2f6fd19378c064af8d7704fb84ef8b740ff97f7ec7609bd6de76348921fcc227e1ce97127947a0d22c7887
@bitcoin bitcoin locked as resolved and limited conversation to collaborators Sep 8, 2021
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@laanwj laanwj laanwj left review comments

@theuni theuni theuni left review comments

@sipa sipa sipa left review comments

@gmaxwell gmaxwell gmaxwell approved these changes

@dcousens dcousens dcousens approved these changes

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9 participants
@TheBlueMatt @meshcollider @achow101 @sipa @paveljanik @laanwj @dcousens @theuni @gmaxwell