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* [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore @ 2022-04-14 13:47 denis.campredon at gmail dot com 2022-04-19 8:29 ` [Bug tree-optimization/105276] " rguenth at gcc dot gnu.org ` (4 more replies) 0 siblings, 5 replies; 6+ messages in thread From: denis.campredon at gmail dot com @ 2022-04-14 13:47 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276 Bug ID: 105276 Summary: [12 Regression] executed once loop not optimized anymore Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: denis.campredon at gmail dot com Target Milestone: --- bool foo(unsigned i) { bool result = true; while (i) { i = i % 3; i = i - (i==2 ? 2 : i ? 1 : 0); result = !result; } return result; } -------------- compiled with g++ 11.2 and -O2 it produces: ----------------- foo(unsigned int): test edi, edi sete al ret ---------------- With current trunk and -02 lots of instructions are generated, the loop is still present, about 30 instructions are produced. Also, when compiled with -Os trunk produces loopless assembly: ------------------ foo(unsigned int): mov dl, 1 test edi, edi je .L1 xor edx, edx .L1: mov eax, edx ret ------------------- Whereas using -Os and g++ 11.2 it uses one less register: ------------------ foo(unsigned int): mov al, 1 test edi, edi je .L4 xor eax, eax .L4: ret ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105276] [12 Regression] executed once loop not optimized anymore 2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com @ 2022-04-19 8:29 ` rguenth at gcc dot gnu.org 2022-04-20 15:38 ` jakub at gcc dot gnu.org ` (3 subsequent siblings) 4 siblings, 0 replies; 6+ messages in thread From: rguenth at gcc dot gnu.org @ 2022-04-19 8:29 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |missed-optimization, | |needs-bisection Component|c |tree-optimization Target Milestone|--- |12.0 --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- likely jump threading changes ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105276] [12 Regression] executed once loop not optimized anymore 2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com 2022-04-19 8:29 ` [Bug tree-optimization/105276] " rguenth at gcc dot gnu.org @ 2022-04-20 15:38 ` jakub at gcc dot gnu.org 2022-04-21 15:46 ` amacleod at redhat dot com ` (2 subsequent siblings) 4 siblings, 0 replies; 6+ messages in thread From: jakub at gcc dot gnu.org @ 2022-04-20 15:38 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276 Jakub Jelinek <jakub at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords|needs-bisection | CC| |amacleod at redhat dot com, | |jakub at gcc dot gnu.org Ever confirmed|0 |1 Status|UNCONFIRMED |NEW Last reconfirmed| |2022-04-20 --- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Started with r12-5688-gcb137e85720654e41db370d952df226654e576a6 The difference starts in vrp2, where the actual IL change is: - _5 = (bool) i_16; - _12 = i_16; + _5 = i_16 != 0; + _12 = (unsigned int) _5; and the ranges changes are: -i_1 : unsigned int [0, 1] +i_1 : unsigned int [0, 2] i_7 : unsigned int [0, 2] -i_8 : unsigned int [0, 1][+INF, +INF] +i_8 : unsigned int [0, 2][+INF, +INF] _12 : unsigned int [0, 1] i_13 : unsigned int [1, +INF] -i_14 : unsigned int [1, 1][+INF, +INF] -i_16 : unsigned int [0, 1] +i_14 : unsigned int [1, 2][+INF, +INF] +i_16 : unsigned int [0, 2] The old ranges were narrower and I think correct. i_7 = i_13 % 3; ... if (i_7 != 2) ... # i_16 = PHI <i_7(3), i_1(5)> _5 = i_16 != 0; _12 = (unsigned int) _5; i_8 = i_16 - _12; if (i_8 != 0) ... # i_14 = PHI <i_8(4)> i_1 = i_14 % 3; Now, that i = i % 3; (i==2 ? 2 : i ? 1 : 0) in the source is just an obfuscated way of saying i = i % 3; i so obviously the loop will iterate at most once (0 times if i is 0, otherwise there will be i = i - i; and it will be zero at the end of the first iteration). That is something the ranger doesn't need to decipher obviously, but the above means i_7 is [0, 2], on i_16 PHI i_7 is known to be [0, 1], so assuming it comes from that edge, i_8 is [0, 1][+INF, +INF] aka ~[2, 0xfffffffe], for 0 it doesn't even jump to i_14 PHI (but 0 % 3 is 0), for i_14 == 1 is 1 % 3 1 and for i_14 == -1U is -1U % 3 == 0. So, i_1 is in [0, 1] range and loops, so the original assumptions that i_16 is [0, 1] don't change. ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105276] [12 Regression] executed once loop not optimized anymore 2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com 2022-04-19 8:29 ` [Bug tree-optimization/105276] " rguenth at gcc dot gnu.org 2022-04-20 15:38 ` jakub at gcc dot gnu.org @ 2022-04-21 15:46 ` amacleod at redhat dot com 2022-04-25 13:59 ` cvs-commit at gcc dot gnu.org 2022-04-25 14:27 ` amacleod at redhat dot com 4 siblings, 0 replies; 6+ messages in thread From: amacleod at redhat dot com @ 2022-04-21 15:46 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276 --- Comment #3 from Andrew Macleod <amacleod at redhat dot com> --- Created attachment 52848 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52848&action=edit proposed patch When I removed the recursion from range_of_stmt, I neglected to incorporate the existing known global range for an ssa-name into the calculated value. Range_of_stmt does this, but the prefill calculation missed it. This patch fixes that oversight. ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105276] [12 Regression] executed once loop not optimized anymore 2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com ` (2 preceding siblings ...) 2022-04-21 15:46 ` amacleod at redhat dot com @ 2022-04-25 13:59 ` cvs-commit at gcc dot gnu.org 2022-04-25 14:27 ` amacleod at redhat dot com 4 siblings, 0 replies; 6+ messages in thread From: cvs-commit at gcc dot gnu.org @ 2022-04-25 13:59 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276 --- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Andrew Macleod <amacleod@gcc.gnu.org>: https://gcc.gnu.org/g:362e2a9c6297203bcf7f66bfb51dffb82b42d3b3 commit r12-8246-g362e2a9c6297203bcf7f66bfb51dffb82b42d3b3 Author: Andrew MacLeod <amacleod@redhat.com> Date: Mon Apr 25 09:56:35 2022 -0400 Retain existing range knowledge when prefilling statements. When range_of_stmt was adjusted to avoid large recursion depth, we need to intersect the calculated range whth the any known range to avoid losing info. Range_of_stmt does this, but the new prefill code missed it. PR tree-optimization/105276 gcc/ * gimple-range.cc (gimple_ranger::prefill_stmt_dependencies): Include existing global range with calculated value. gcc/testsuite/ * g++.dg/pr105276.C: New. ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/105276] [12 Regression] executed once loop not optimized anymore 2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com ` (3 preceding siblings ...) 2022-04-25 13:59 ` cvs-commit at gcc dot gnu.org @ 2022-04-25 14:27 ` amacleod at redhat dot com 4 siblings, 0 replies; 6+ messages in thread From: amacleod at redhat dot com @ 2022-04-25 14:27 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105276 Andrew Macleod <amacleod at redhat dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|--- |FIXED Status|NEW |RESOLVED --- Comment #5 from Andrew Macleod <amacleod at redhat dot com> --- fixed. ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2022-04-25 14:27 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-04-14 13:47 [Bug c/105276] New: [12 Regression] executed once loop not optimized anymore denis.campredon at gmail dot com 2022-04-19 8:29 ` [Bug tree-optimization/105276] " rguenth at gcc dot gnu.org 2022-04-20 15:38 ` jakub at gcc dot gnu.org 2022-04-21 15:46 ` amacleod at redhat dot com 2022-04-25 13:59 ` cvs-commit at gcc dot gnu.org 2022-04-25 14:27 ` amacleod at redhat dot com
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