[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 --- Comment #13 from Richard Biener --- *** Bug 89791 has been marked as a duplicate of this bug. ***
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 --- Comment #11 from Richard Biener --- Author: rguenth Date: Wed Mar 27 09:31:53 2019 New Revision: 269961 URL: https://gcc.gnu.org/viewcvs?rev=269961=gcc=rev Log: 2019-03-27 Richard Biener PR tree-optimization/89463 * tree-ssa-dce.c (remove_dead_stmt): Take output vector to queue edges to remove. (eliminate_unnecessary_stmts): Remove dead PHIs alongside dead stmts. Delay edge removal until PHIs are removed to make debug-stmt creation not confused by seemingly degenerate PHIs. * gcc.dg/guality/pr89463.c: New testcase. Added: trunk/gcc/testsuite/gcc.dg/guality/pr89463.c Modified: trunk/gcc/ChangeLog trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-ssa-dce.c
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 Richard Biener changed: What|Removed |Added Status|ASSIGNED|RESOLVED Known to work||9.0 Resolution|--- |FIXED Known to fail||8.3.0 --- Comment #12 from Richard Biener --- Fixed for GCC 9.
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 --- Comment #9 from Qirun Zhang --- (In reply to Richard Biener from comment #8) > Patch posted here: https://gcc.gnu.org/ml/gcc-patches/2019-03/msg01192.html > > Some of your bugs might turn out as duplicates if they are fixed by that > patch. Thanks, Richard. When will the patch be landed? It helps a lot to reduce duplicates.
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 --- Comment #10 from rguenther at suse dot de --- On Mon, 25 Mar 2019, qrzhang at gatech dot edu wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 > > --- Comment #9 from Qirun Zhang --- > (In reply to Richard Biener from comment #8) > > Patch posted here: https://gcc.gnu.org/ml/gcc-patches/2019-03/msg01192.html > > > > Some of your bugs might turn out as duplicates if they are fixed by that > > patch. > > Thanks, Richard. When will the patch be landed? It helps a lot to reduce > duplicates. I'm waiting for testing/ACK.
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 --- Comment #8 from Richard Biener --- Patch posted here: https://gcc.gnu.org/ml/gcc-patches/2019-03/msg01192.html Some of your bugs might turn out as duplicates if they are fixed by that patch.
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 Richard Biener changed: What|Removed |Added Status|NEW |ASSIGNED Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org --- Comment #7 from Richard Biener --- : # i_5 = PHI <_11(5), 0(8)> # DEBUG i => i_5 if (i_5 != 6) goto ; [INV] else goto ; [100.00%] : # DEBUG BEGIN_STMT # DEBUG i => i_5 + 1 So it goes like so the following. First we remove the iterator update in BB5 (unrelated). Then we remove the control stmt, removing the edge 6 -> 5. This leaves us with # i_5 = PHI <0(8)> # DEBUG i => i_5 then we remove the PHI node which inserts the bogus debug stmt. Stmt and control-flow removal in DCE is somewhat a twisted maze but the fix has to be there, avoiding the above situation. For simple IVs we could compute the final value and insert a debug stmt after the loop. But for IVs we cannot analyze a similar situation will arise and thus we have to somehow compute a # DEBUG i => NULL stmt from the above. But that means we have to queue edges we want to remove (plus eventually blocks we can avoid looking at for stmt removal) and perform CFG pruning only afterwards (like leave it to CFG cleanup by changing conditionals to if (true/false)). Doing that (just for conditions) gives us the expected @@ -24,22 +52,10 @@ if (a.1_3 <= 9) goto ; [INV] else -goto ; [INV] - - : - # DEBUG BEGIN_STMT - i_11 = i_5 + 1; - # DEBUG i => i_11 - - : - # i_5 = PHI - # DEBUG i => i_5 - if (i_5 != 6) goto ; [INV] - else -goto ; [INV] - : + : + # DEBUG i => NULL # DEBUG BEGIN_STMT optimize_me_not (); return 0; but that's not because of CFG cleanup but because we do not remove the edge so at PHI removal time we still have both values. A non-loopy testcase may also go wrong I guess but it's usually optimized earlier and not by DCE. I have a patch.
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 --- Comment #6 from Qirun Zhang --- As mentioned in my earlier comment, the revision should be between gcc-5 and gcc-6. Bisect points to r239357. commit ec969ce4161538b561592a032eca6dcfaf513596 Author: rguenth Date: Thu Aug 11 09:02:04 2016 + 2016-08-11 Richard Biener PR tree-optimization/72772 * cfgloopmanip.c (create_preheader): Use split_edge if there is a single loop entry, avoiding degenerate PHIs. * gcc.dg/graphite/pr35356-1.c: Adjust. * gcc.dg/tree-ssa/pr59597.c: Likewise. git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@239357 138bc75d-0d04-0410-961f-82ee72b054a4
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 --- Comment #5 from Qirun Zhang --- (In reply to Qirun Zhang from comment #4) > Bisect points to r151362. > > commit ff79704e04af919c4fe501c7dceca8b21cced614 > Author: aoliva > Date: Thu Sep 3 05:24:57 2009 + > > * toplev.c (process_options): Enable var-tracking-assignments > by default if var-tracking is enabled. > > > git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@151362 > 138bc75d-0d04-0410-961f-82ee72b054a4 Sorry... Please discard this comment. This was meant for another bug. Let me post the bisect result in the following comment..
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 --- Comment #4 from Qirun Zhang --- Bisect points to r151362. commit ff79704e04af919c4fe501c7dceca8b21cced614 Author: aoliva Date: Thu Sep 3 05:24:57 2009 + * toplev.c (process_options): Enable var-tracking-assignments by default if var-tracking is enabled. git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@151362 138bc75d-0d04-0410-961f-82ee72b054a4
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 Richard Biener changed: What|Removed |Added Keywords||wrong-debug Status|UNCONFIRMED |NEW Last reconfirmed||2019-02-26 Version|unknown |9.0 Ever confirmed|0 |1 Severity|enhancement |normal --- Comment #3 from Richard Biener --- stmt removal should generate a # DEBUG i = NULL note but eventually removal inside a CFG cycle is awkward enough that this doesn't work reliably. In fact we seem to get an extra = 0 note, likely from the attempt to generate a i => i_5 one. --- t.i.036t.dse1 2019-02-26 09:46:03.325257454 +0100 +++ t.i.037t.cddce1 2019-02-26 09:46:03.329257503 +0100 ... @@ -24,22 +52,10 @@ if (a.1_3 <= 9) goto ; [INV] else -goto ; [INV] - - : - # DEBUG BEGIN_STMT - i_11 = i_5 + 1; - # DEBUG i => i_11 - - : - # i_5 = PHI - # DEBUG i => i_5 - if (i_5 != 6) goto ; [INV] - else -goto ; [INV] - : + : + # DEBUG i => 0 # DEBUG BEGIN_STMT optimize_me_not (); return 0;
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 --- Comment #2 from Qirun Zhang --- (In reply to Andrew Pinski from comment #1) > What is happening is the empty loop is being removed and not replaced with a > debug statement say i is 6 afterwards. I don't know if this is a good idea > to put a debug statement here or not. Agreed. Nevertheless, it should not print a wrong value. The expected behavior is "" like what gcc-6.5.0 does as follows: $ gcc-6 -O3 out.c abc.c -g $ gdb-trunk -x cmds -batch a.out Breakpoint 1 at 0x547: file abc.c, line 8. Breakpoint 1, main () at abc.c:8 8 optimize_me_not(); $1 = Kill the program being debugged? (y or n) [answered Y; input not from terminal] [Inferior 1 (process 17644) killed]
[Bug debug/89463] debug information for iteractor of an empty loop is gone (at -O3)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89463 Andrew Pinski changed: What|Removed |Added Summary|gcc generates wrong debug |debug information for |information at -O3 |iteractor of an empty loop ||is gone (at -O3) Severity|normal |enhancement --- Comment #1 from Andrew Pinski --- What is happening is the empty loop is being removed and not replaced with a debug statement say i is 6 afterwards. I don't know if this is a good idea to put a debug statement here or not.
