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* [Bug c++/56292] New: False positive for constexpr arithmetics (-Wconversion)
@ 2013-02-12 8:07 lcid-fire at gmx dot net
2013-02-12 9:04 ` [Bug c++/56292] " jakub at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: lcid-fire at gmx dot net @ 2013-02-12 8:07 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56292
Bug #: 56292
Summary: False positive for constexpr arithmetics
(-Wconversion)
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c++
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: lcid-fire@gmx.net
For the following code one gets 'conversion' diagnostics, while the compiler
should be able to compute, that it is actually fine.
#include <cstdint>
constexpr std::uint8_t func() { return 2; }
std::uint8_t value = func() + 2;
Results in:
warning: conversion to ‘uint8_t {aka unsigned char}’ from ‘int’ may alter its
value [-Wconversion]
Diagnostics works fine if you replace 'func()' with a number.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/56292] False positive for constexpr arithmetics (-Wconversion)
2013-02-12 8:07 [Bug c++/56292] New: False positive for constexpr arithmetics (-Wconversion) lcid-fire at gmx dot net
@ 2013-02-12 9:04 ` jakub at gcc dot gnu.org
2013-02-12 10:13 ` lcid-fire at gmx dot net
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: jakub at gcc dot gnu.org @ 2013-02-12 9:04 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56292
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-12 09:03:44 UTC ---
func() + 2 is evaluated as (unsigned char) (((int) func ()) + 2), so when the
-Wconversion warning is diagnosed before evaluating all the constexpr
expressions into constants if possible, the warning is reasonable.
Consider
constexpr std::uint8_t func() { return 0xff; }
std::uint8_t value = func() + 2;
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/56292] False positive for constexpr arithmetics (-Wconversion)
2013-02-12 8:07 [Bug c++/56292] New: False positive for constexpr arithmetics (-Wconversion) lcid-fire at gmx dot net
2013-02-12 9:04 ` [Bug c++/56292] " jakub at gcc dot gnu.org
@ 2013-02-12 10:13 ` lcid-fire at gmx dot net
2013-02-12 12:29 ` rguenth at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: lcid-fire at gmx dot net @ 2013-02-12 10:13 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56292
--- Comment #2 from lcid-fire at gmx dot net 2013-02-12 10:13:17 UTC ---
But should it be evaluated before constexpr are processed?
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/56292] False positive for constexpr arithmetics (-Wconversion)
2013-02-12 8:07 [Bug c++/56292] New: False positive for constexpr arithmetics (-Wconversion) lcid-fire at gmx dot net
2013-02-12 9:04 ` [Bug c++/56292] " jakub at gcc dot gnu.org
2013-02-12 10:13 ` lcid-fire at gmx dot net
@ 2013-02-12 12:29 ` rguenth at gcc dot gnu.org
2013-02-12 15:24 ` lcid-fire at gmx dot net
2014-11-18 13:44 ` paolo.carlini at oracle dot com
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2013-02-12 12:29 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56292
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-12 12:29:28 UTC ---
Does it also warn if you make value a constexpr?
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/56292] False positive for constexpr arithmetics (-Wconversion)
2013-02-12 8:07 [Bug c++/56292] New: False positive for constexpr arithmetics (-Wconversion) lcid-fire at gmx dot net
` (2 preceding siblings ...)
2013-02-12 12:29 ` rguenth at gcc dot gnu.org
@ 2013-02-12 15:24 ` lcid-fire at gmx dot net
2014-11-18 13:44 ` paolo.carlini at oracle dot com
4 siblings, 0 replies; 6+ messages in thread
From: lcid-fire at gmx dot net @ 2013-02-12 15:24 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56292
--- Comment #4 from lcid-fire at gmx dot net 2013-02-12 15:23:58 UTC ---
constexpr std::uint8_t value = func() + 2;
does generate the same warning.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/56292] False positive for constexpr arithmetics (-Wconversion)
2013-02-12 8:07 [Bug c++/56292] New: False positive for constexpr arithmetics (-Wconversion) lcid-fire at gmx dot net
` (3 preceding siblings ...)
2013-02-12 15:24 ` lcid-fire at gmx dot net
@ 2014-11-18 13:44 ` paolo.carlini at oracle dot com
4 siblings, 0 replies; 6+ messages in thread
From: paolo.carlini at oracle dot com @ 2014-11-18 13:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56292
Paolo Carlini <paolo.carlini at oracle dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Known to work| |4.9.0, 4.9.1, 5.0
Resolution|--- |FIXED
Target Milestone|--- |4.9.0
--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> ---
This is fixed in 4.9.0.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2014-11-18 13:44 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2013-02-12 8:07 [Bug c++/56292] New: False positive for constexpr arithmetics (-Wconversion) lcid-fire at gmx dot net
2013-02-12 9:04 ` [Bug c++/56292] " jakub at gcc dot gnu.org
2013-02-12 10:13 ` lcid-fire at gmx dot net
2013-02-12 12:29 ` rguenth at gcc dot gnu.org
2013-02-12 15:24 ` lcid-fire at gmx dot net
2014-11-18 13:44 ` paolo.carlini at oracle dot com
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