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* [Bug rtl-optimization/37262] New: Two branches of the same condition being emitted @ 2008-08-28 2:03 pinskia at gcc dot gnu dot org 2008-08-29 4:39 ` [Bug rtl-optimization/37262] " pinskia at gcc dot gnu dot org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: pinskia at gcc dot gnu dot org @ 2008-08-28 2:03 UTC (permalink / raw) To: gcc-bugs Take: unsigned ReverseBits (unsigned index, unsigned NumBits) { unsigned i, rev; for (i = rev = 0; i < NumBits; i++) { rev = (rev << 1) | (index & 1); index >>= 1; } return rev; } ---- CUT --- Currently we get: mtctr 9 beq- 7,.L8 beq- 7,.L8 .p2align 3,,7 Which is obviously broken as we should have only one beq as they use the same CR and go to the same block and there is no way to get to the second one without going through the first. 4.1.1 -fno-ivopts produces even worse code: cmplwi 7,4,1 blt- 7,.L8 cmpwi 7,4,0 beq- 7,.L8 But we know that this a logicial compare so r4 < 1 is the same as r4 ==0 so 4.3 produces better code but still needs slight improvement with respect of getting rid of the extra branch (though we have regression between 4.1 and 4.3 which I will file seperately as it is unrelated to this bug). -- Summary: Two branches of the same condition being emitted Product: gcc Version: 4.4.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: rtl-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: pinskia at gcc dot gnu dot org GCC target triplet: powerpc64-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37262 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/37262] Two branches of the same condition being emitted 2008-08-28 2:03 [Bug rtl-optimization/37262] New: Two branches of the same condition being emitted pinskia at gcc dot gnu dot org @ 2008-08-29 4:39 ` pinskia at gcc dot gnu dot org 2008-08-30 1:43 ` pinskia at gcc dot gnu dot org 2010-03-02 18:29 ` pinskia at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu dot org @ 2008-08-29 4:39 UTC (permalink / raw) To: gcc-bugs -- pinskia at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- Severity|normal |enhancement http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37262 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/37262] Two branches of the same condition being emitted 2008-08-28 2:03 [Bug rtl-optimization/37262] New: Two branches of the same condition being emitted pinskia at gcc dot gnu dot org 2008-08-29 4:39 ` [Bug rtl-optimization/37262] " pinskia at gcc dot gnu dot org @ 2008-08-30 1:43 ` pinskia at gcc dot gnu dot org 2010-03-02 18:29 ` pinskia at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu dot org @ 2008-08-30 1:43 UTC (permalink / raw) To: gcc-bugs ------- Comment #1 from pinskia at gcc dot gnu dot org 2008-08-30 01:41 ------- I have seen this in other cases even for the non doloop case, though I don't know if it is because of -O1 or because it is not removing it. Testcase: int _bfd_xcoff_canonicalize_dynamic_reloc (unsigned long long l_symndx) { if (l_symndx < 3) { switch (l_symndx) { case 0: case 1: break; case 2: return _bfd_abort (); } } } --- CUT --- Compile at -O1 on powerpc-linux and you will see the double branches: bne 0,.L7 bne 0,.L8 -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37262 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/37262] Two branches of the same condition being emitted 2008-08-28 2:03 [Bug rtl-optimization/37262] New: Two branches of the same condition being emitted pinskia at gcc dot gnu dot org 2008-08-29 4:39 ` [Bug rtl-optimization/37262] " pinskia at gcc dot gnu dot org 2008-08-30 1:43 ` pinskia at gcc dot gnu dot org @ 2010-03-02 18:29 ` pinskia at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu dot org @ 2010-03-02 18:29 UTC (permalink / raw) To: gcc-bugs ------- Comment #2 from pinskia at gcc dot gnu dot org 2010-03-02 18:29 ------- Still happens as of today on the trunk. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37262 ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2010-03-02 18:29 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2008-08-28 2:03 [Bug rtl-optimization/37262] New: Two branches of the same condition being emitted pinskia at gcc dot gnu dot org 2008-08-29 4:39 ` [Bug rtl-optimization/37262] " pinskia at gcc dot gnu dot org 2008-08-30 1:43 ` pinskia at gcc dot gnu dot org 2010-03-02 18:29 ` pinskia at gcc dot gnu dot org
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