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* [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple @ 2021-11-19 1:35 pinskia at gcc dot gnu.org 2021-11-19 1:36 ` [Bug tree-optimization/103325] " pinskia at gcc dot gnu.org ` (3 more replies) 0 siblings, 4 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-11-19 1:35 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103325 Bug ID: 103325 Summary: 1 << -1 is never reduced to a constant during gimple Product: gcc Version: 12.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: enhancement Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: pinskia at gcc dot gnu.org Target Milestone: --- Take: int main() { return 1 >> (-1); } GCC is the only compiler I have tried (MSVC, ICC and clang/LLVM) which does not remove the shift. Yes this is undefined behavior but really I think it is best to reduce to something rather than keeping around the shift. Even converting it to __builtin_unreachable will be ok in my book. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/103325] 1 << -1 is never reduced to a constant during gimple 2021-11-19 1:35 [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple pinskia at gcc dot gnu.org @ 2021-11-19 1:36 ` pinskia at gcc dot gnu.org 2021-11-19 7:48 ` rguenth at gcc dot gnu.org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-11-19 1:36 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103325 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- I should note I noticed this while working on PR 103314. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/103325] 1 << -1 is never reduced to a constant during gimple 2021-11-19 1:35 [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple pinskia at gcc dot gnu.org 2021-11-19 1:36 ` [Bug tree-optimization/103325] " pinskia at gcc dot gnu.org @ 2021-11-19 7:48 ` rguenth at gcc dot gnu.org 2021-11-19 12:14 ` pinskia at gcc dot gnu.org 2023-05-28 4:21 ` pinskia at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: rguenth at gcc dot gnu.org @ 2021-11-19 7:48 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103325 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2021-11-19 Ever confirmed|0 |1 --- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> --- I think we used to constant fold this as 1<<1. GCC 7 does > gcc-7 -S t.c -fdump-tree-original t.c: In function 'main': t.c:2:12: warning: right shift count is negative [-Wshift-count-negative] return 1 >> (-1); ^~ > cat t.c.003t.original ;; Function main (null) ;; enabled by -tree-original { return 2; } return 0; but IIRC that behavior was removed from {int_const,wide}_int_binop at some point, maybe also to enable sanitization. gimple-ssa-isolate-paths.c would be one place to turn such code into unreachable or traps (see other PRs to make the behavior configurable). ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/103325] 1 << -1 is never reduced to a constant during gimple 2021-11-19 1:35 [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple pinskia at gcc dot gnu.org 2021-11-19 1:36 ` [Bug tree-optimization/103325] " pinskia at gcc dot gnu.org 2021-11-19 7:48 ` rguenth at gcc dot gnu.org @ 2021-11-19 12:14 ` pinskia at gcc dot gnu.org 2023-05-28 4:21 ` pinskia at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-11-19 12:14 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103325 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- See Also| |https://gcc.gnu.org/bugzill | |a/show_bug.cgi?id=96929 --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- (In reply to Richard Biener from comment #2) > but IIRC that behavior was removed from {int_const,wide}_int_binop at some > point, maybe also to enable sanitization. This was only done in GCC 11 by r11-5271-g4866b2f5db117f9 (PR96929). ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/103325] 1 << -1 is never reduced to a constant during gimple 2021-11-19 1:35 [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple pinskia at gcc dot gnu.org ` (2 preceding siblings ...) 2021-11-19 12:14 ` pinskia at gcc dot gnu.org @ 2023-05-28 4:21 ` pinskia at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-05-28 4:21 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103325 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|--- |FIXED Target Milestone|--- |12.3 Status|NEW |RESOLVED --- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Fixed for GCC 12.3.0 by r12-9091-g9dccaeaa586a16 (aka PR 108306 ). So closing as fixed. Note DOM and VRP both do it so it is done at -O1 and -O2. ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2023-05-28 4:21 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-11-19 1:35 [Bug tree-optimization/103325] New: 1 << -1 is never reduced to a constant during gimple pinskia at gcc dot gnu.org 2021-11-19 1:36 ` [Bug tree-optimization/103325] " pinskia at gcc dot gnu.org 2021-11-19 7:48 ` rguenth at gcc dot gnu.org 2021-11-19 12:14 ` pinskia at gcc dot gnu.org 2023-05-28 4:21 ` pinskia at gcc dot gnu.org
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