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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/82885] memcpy does not propagate aliasing knowledge Date: Sun, 01 Aug 2021 17:07:09 +0000 [thread overview] Message-ID: <bug-82885-4-mEPfOqn4OG@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-82885-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82885 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Component|middle-end |tree-optimization Severity|normal |enhancement --- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> --- The original testcase is fixed in GCC 8+: <bb 2> [local count: 1073741825]: __builtin_memcpy (ch1_3(D), ch2_4(D), 1048576); _1 = MEM[(const char *)ch2_4(D) + 2B]; *ch1_3(D) = _1; MEM[(char *)ch1_3(D) + 1B] = _1; fre1 is able to figure this out but this is not exactly propagating aliasing info, just that the value of ch2[2] cannot change if ch1[0] is stored with the same value of what was in ch2[2]; memcpy is not needed to show that :). A better testcase which shows there is still a missing aliasing case: void foo3(char* ch1, char* ch2) { __builtin_memcpy(ch1, ch2, 1024*1024); ch1[0] = ch2[2] + 1; ch1[1] = ch2[2]; }
parent reply other threads:[~2021-08-01 17:07 UTC|newest] Thread overview: expand[flat|nested] mbox.gz Atom feed [parent not found: <bug-82885-4@http.gcc.gnu.org/bugzilla/>]
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