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* [Bug c/54149] New: write introduction incorrect wrt the C11 memory model @ 2012-08-01 8:47 francesco.zappa.nardelli at gmail dot com 2012-08-23 16:35 ` [Bug c/54149] " francesco.zappa.nardelli at gmail dot com ` (3 more replies) 0 siblings, 4 replies; 5+ messages in thread From: francesco.zappa.nardelli at gmail dot com @ 2012-08-01 8:47 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54149 Bug #: 54149 Summary: write introduction incorrect wrt the C11 memory model Classification: Unclassified Product: gcc Version: 4.8.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned@gcc.gnu.org ReportedBy: francesco.zappa.nardelli@gmail.com [ possibly related to http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52558 ] Consider this program: int g_13 = 1; void main () { int l_245; for (l_245 = 0; l_245 <= 1; l_245 += 1) for (; g_13 <= 0; g_13 = 1); } If I compile it with gcc --param allow-store-data-races=0 -S -O1 (I am running gcc (GCC) 4.8.0 20120627 (experimental) on Linux - x86_64 -- the same applies to -O2 and -O3 and compilation with g++ -std=c++11 -O1) I get the following optimised assembler (I just hand removed some noise): main: movl g_13(%rip), %eax testl %eax, %eax movl $1, %edx cmovle %edx, %eax movl %eax, g_13(%rip) ret g_13: .long 1 which always performs a write to g_13 and executes with this memory trace (I am tracing only the accesses to the global - potentially shared - variables): g_13 1 4 Init g_13 1 4 Load g_13 1 4 Store However the reference trace for the C11 program above never performs a write to g_13: g_13 1 4 Init g_13 1 4 Load g_13 1 4 Load This looks related to the problem I reported in http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52558 , as the optimiser introduces a memory write which should not be there (and in turn performs an optimisation not correct wrt the C11 or the C++11 memory model). The same discriminating context of bug 52558 applies. For reference: $ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/home/yquem/moscova/zappa/source/gcc-svn-bin/libexec/gcc/x86_64-unknown-linux-gnu/4.8.0/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: ../gcc-svn/configure --prefix=/home/yquem/moscova/zappa/source/gcc-svn-bin/ Thread model: posix gcc version 4.8.0 20120627 (experimental) (GCC) ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/54149] write introduction incorrect wrt the C11 memory model 2012-08-01 8:47 [Bug c/54149] New: write introduction incorrect wrt the C11 memory model francesco.zappa.nardelli at gmail dot com @ 2012-08-23 16:35 ` francesco.zappa.nardelli at gmail dot com 2012-09-07 19:45 ` aldyh at gcc dot gnu.org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: francesco.zappa.nardelli at gmail dot com @ 2012-08-23 16:35 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54149 --- Comment #1 from Francesco Zappa Nardelli <francesco.zappa.nardelli at gmail dot com> 2012-08-23 16:34:38 UTC --- Here is another C program that hits a similar write-introduction problem: int g_7, g_372; char func_10 () { for (; g_7 < 0; ++g_7) { } return 0; } void main () { int l_8; lbl_914: (l_8 = g_7) <= func_10 (); if (l_8) if (g_372) { } else goto lbl_914; } The reference trace is: *** unoptimised trace: gcc --param allow-store-data-races=0 8-min.c -o 8-min_unopt g_7 0 4 Init g_372 0 4 Init g_7 0 4 Load g_7 0 4 Load while the optimised trace (requires -O2 or -O3 to be observable) is *** optimised trace: gcc --param allow-store-data-races=0 -O3 8-min.c -o 8-min_opt g_7 0 4 Init g_372 0 4 Init g_372 0 4 Load g_7 0 4 Load g_7 0 4 Store [ gcc version 4.8.0 20120627 (experimental) (GCC) ] ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/54149] write introduction incorrect wrt the C11 memory model 2012-08-01 8:47 [Bug c/54149] New: write introduction incorrect wrt the C11 memory model francesco.zappa.nardelli at gmail dot com 2012-08-23 16:35 ` [Bug c/54149] " francesco.zappa.nardelli at gmail dot com @ 2012-09-07 19:45 ` aldyh at gcc dot gnu.org 2012-09-11 12:28 ` [Bug middle-end/54149] " aldyh at gcc dot gnu.org 2012-09-11 12:30 ` aldyh at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: aldyh at gcc dot gnu.org @ 2012-09-07 19:45 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54149 Aldy Hernandez <aldyh at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2012-09-07 CC| |amacleod at redhat dot com AssignedTo|unassigned at gcc dot |aldyh at gcc dot gnu.org |gnu.org | Ever Confirmed|0 |1 --- Comment #2 from Aldy Hernandez <aldyh at gcc dot gnu.org> 2012-09-07 19:45:29 UTC --- This looks like a data race introduced by LIM. Ughh, I thought I had this pass all fixed... I'll take a look. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/54149] write introduction incorrect wrt the C11 memory model 2012-08-01 8:47 [Bug c/54149] New: write introduction incorrect wrt the C11 memory model francesco.zappa.nardelli at gmail dot com 2012-08-23 16:35 ` [Bug c/54149] " francesco.zappa.nardelli at gmail dot com 2012-09-07 19:45 ` aldyh at gcc dot gnu.org @ 2012-09-11 12:28 ` aldyh at gcc dot gnu.org 2012-09-11 12:30 ` aldyh at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: aldyh at gcc dot gnu.org @ 2012-09-11 12:28 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54149 --- Comment #3 from Aldy Hernandez <aldyh at gcc dot gnu.org> 2012-09-11 12:28:11 UTC --- Author: aldyh Date: Tue Sep 11 12:28:02 2012 New Revision: 191179 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191179 Log: PR middle-end/54149 * tree-ssa-loop-im.c (execute_sm_if_changed_flag_set): Only set flag for writes. Added: trunk/gcc/testsuite/gcc.dg/simulate-thread/speculative-store-4.c Modified: trunk/gcc/ChangeLog trunk/gcc/tree-ssa-loop-im.c ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/54149] write introduction incorrect wrt the C11 memory model 2012-08-01 8:47 [Bug c/54149] New: write introduction incorrect wrt the C11 memory model francesco.zappa.nardelli at gmail dot com ` (2 preceding siblings ...) 2012-09-11 12:28 ` [Bug middle-end/54149] " aldyh at gcc dot gnu.org @ 2012-09-11 12:30 ` aldyh at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: aldyh at gcc dot gnu.org @ 2012-09-11 12:30 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54149 Aldy Hernandez <aldyh at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution| |FIXED --- Comment #4 from Aldy Hernandez <aldyh at gcc dot gnu.org> 2012-09-11 12:30:36 UTC --- fixed on trunk ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2012-09-11 12:30 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2012-08-01 8:47 [Bug c/54149] New: write introduction incorrect wrt the C11 memory model francesco.zappa.nardelli at gmail dot com 2012-08-23 16:35 ` [Bug c/54149] " francesco.zappa.nardelli at gmail dot com 2012-09-07 19:45 ` aldyh at gcc dot gnu.org 2012-09-11 12:28 ` [Bug middle-end/54149] " aldyh at gcc dot gnu.org 2012-09-11 12:30 ` aldyh at gcc dot gnu.org
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