Bug 47900 - Missed optimization with LTO
Summary: Missed optimization with LTO
Status: RESOLVED WORKSFORME
Alias: None
Product: gcc
Classification: Unclassified
Component: lto (show other bugs)
Version: 4.6.0
: P3 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL:
Keywords: lto, missed-optimization
Depends on:
Blocks:
 
Reported: 2011-02-26 04:40 UTC by Dmitry Gorbachev
Modified: 2013-02-07 00:13 UTC (History)
0 users

See Also:
Host: i686-pc-linux-gnu
Target: i686-pc-linux-gnu
Build: i686-pc-linux-gnu
Known to work:
Known to fail: 4.5.3, 4.6.0
Last reconfirmed: 2011-02-27 15:13:22

Attachments
Testcase (321 bytes, text/plain)
2011-02-26 04:40 UTC, Dmitry Gorbachev 		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 Dmitry Gorbachev 2011-02-26 04:40:13 UTC 
Created attachment 23474 [details]
Testcase
Comment 1 Richard Biener 2011-02-27 15:13:22 UTC 
I fail to see what the missed optimization is, can you try to explain?
Comment 2 Dmitry Gorbachev 2011-02-27 19:57:01 UTC 
A null pointer check (... && ! &p->i) is not eliminated, notwithstanding the fact that the pointer has been dereferenced. If it is not null, bar is not called; otherwise, there is an undefined behavior, and bar is not called.

Or is it too an unimportant problem?

(It's interesting, after changing S_ptr p to struct S *p, the non-LTO build also fails with "undefined reference to `bar'".)
Comment 3 Richard Biener 2011-02-27 20:03:05 UTC 
Hm, ok.  It's surely worth investigating.
Comment 4 Dmitry Gorbachev 2013-02-07 00:13:03 UTC 
I can't reproduce it with GCC 4.6.4, 4.7.3, 4.8.0.