Bug 80633 - [7/8 Regression] -Wstrict-aliasing false positive
Summary: [7/8 Regression] -Wstrict-aliasing false positive
Status: RESOLVED FIXED
Alias: None
Product: gcc
Classification: Unclassified
Component: c++ (show other bugs)
Version: 7.1.1
: P3 normal
Target Milestone: 7.2
Assignee: Not yet assigned to anyone
URL:
Keywords: diagnostic
Depends on:
Blocks:
 
Reported: 2017-05-04 20:23 UTC by Casey Carter
Modified: 2017-06-20 18:51 UTC (History)
3 users (show)

See Also:
Host:
Target:
Build:
Known to work:
Known to fail:
Last reconfirmed: 2017-06-19 00:00:00

Attachments
Repro (sorry, not library-free) (90 bytes, text/plain)
2017-05-04 20:23 UTC, Casey Carter 		Details
View All Add an attachment (proposed patch, testcase, etc.)

Note You need to log in before you can comment on or make changes to this bug.
Description Casey Carter 2017-05-04 20:23:46 UTC 
Created attachment 41321 [details]
Repro (sorry, not library-free)

gcc 7.1.1 20170504 and 8.0.0 20170504 - but not 6.2/5.4/4.9.4 - incorrectly diagnose this program:

#include <fstream>

extern void f(std::istream&);
std::ifstream ss;
using T = decltype(f(ss)); // warning: dereferencing type-punned pointer will break strict-aliasing rules

when compiling with "gcc -Wstrict-aliasing -O2 -c". The diagnostic is notably not emitted for "decltype(f(std::declval<std::ifstream&>()))".
Comment 1 Jason Merrill 2017-06-19 19:53:03 UTC 
I can't reproduce this with 20170619.  Are you still seeing it?
Comment 2 Casey Carter 2017-06-19 20:35:46 UTC 
(In reply to Jason Merrill from comment #1)
> I can't reproduce this with 20170619.  Are you still seeing it?

Nope - it appears to have disappeared on trunk.
Comment 3 Jason Merrill 2017-06-20 18:51:05 UTC 
Then closing as fixed.