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memcpy of a small const array is incorrectly compiled inline under -O2 or -O3 optimization, but not -O Release: GCC 3.2 Environment: Gentoo Linux 1.4 Reading specs from /usr/lib/gcc-lib/i686-pc-linux-gnu/3.2/specs Configured with: /var/tmp/portage/gcc-3.2-r2/work/gcc-3.2/configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --target=i686-pc-linux-gnu --with-system-zlib --enable-languages=c,c++,ada,f77,objc,java --enable-threads=posix --enable-long-long --disable-checking --enable-cstdio=stdio --enable-clocale=generic --enable-__cxa_atexit --enable-version-specific-runtime-libs --with-gxx-include-dir=/usr/include/g++-v32 --with-local-prefix=/usr/local --enable-shared --enable-nls --without-included-gettext Thread model: posix gcc version 3.2 How-To-Repeat: compile and run the attachment and observe the output: the program performs the memcpy and then prints one line for each element of the arrays, first the source then the destination. under -O2 optimization, the 2nd 3rd and 4th bytes of the dest array are garbbled.
State-Changed-From-To: open->analyzed State-Changed-Why: Confirmed. This program ---------------------------- #include <stdio.h> #include <string.h> int main() { char* buffer = new char[8]; const char head[8] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H' }; memcpy(buffer,head,8); for(int i=0;i<8;i++) printf ("[%u] = %c, %c\n", i, head[i], buffer[i]); return 0; } -------------------------------- yields with 3.2.2pre, 3.3pre, and 2.95 respectively: tmp/g> /home/bangerth/bin/gcc-3.2.2-pre/bin/c++ -O2 bug.cc && ./a.out [0] = A, A [1] = B, [2] = C, [3] = D, [4] = E, E [5] = F, F [6] = G, G [7] = H, H tmp/g> /home/bangerth/bin/gcc-3.3-pre/bin/c++ -O2 bug.cc && ./a.out [0] = A, A [1] = B, [2] = C, [3] = D, [4] = E, E [5] = F, F [6] = G, G [7] = H, H tmp/g> c++ -O2 bug.cc && ./a.out [0] = A, A [1] = B, B [2] = C, C [3] = D, D [4] = E, E [5] = F, F [6] = G, G [7] = H, H That seems like a regression.
From: Glen Nakamura <glen@imodulo.com> To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org Cc: Subject: Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2 Date: Mon, 9 Dec 2002 22:20:00 -1000 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8634 Additional analysis of the problem and work-around patch posted at: http://gcc.gnu.org/ml/gcc-patches/2002-12/msg00533.html GCC developers with more experience should decide whether or not const initializers should be flagged as RTX_UNCHANGING, and if so then the cases that generate multiple sets need to be fixed... - glen
From: Janis Johnson <janis187@us.ibm.com> To: gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org, duchier@ps.uni-sb.de, gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org Cc: Subject: Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2 Date: Mon, 23 Dec 2002 16:37:21 -0800 The regression reported in PR optimization/8634 showed up starting with this patch (strange but true): Fri Dec 21 23:30:14 CET 2001 Jan Hubicka <jh@suse.cz> * i386.h (TARGET_CPU_DEFAULT_pentium_mmx): New. (TARGET_CPU_DEFAULT_*): Renumber. I used this test case that Wolfgang provided. It aborts when the wrong code is generated for -O2 on i686-linux: -------------- /* incorrect code for inlining of memcpy under -O2 */ #include <string.h> #include <stdlib.h> int main () { int i; char buffer[8]; const char head[8] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H' }; memcpy (buffer, head, 8); for (i = 0; i < 8; i++) if (head[i] != buffer[i]) abort (); return 0; } -------------- http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8634
From: Glen Nakamura <glen@imodulo.com> To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org Cc: Subject: Re: optimization/8634: [3.2/3.3 regression] incorrect code for inlining of memcpy under -O2 Date: Sun, 23 Mar 2003 18:07:39 +0000 --wRRV7LY7NUeQGEoC Content-Type: text/plain; charset=us-ascii Content-Disposition: inline http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8634 Attached is an extended test case for constant initializers. --wRRV7LY7NUeQGEoC Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="pr8634.c" /* PR optimization/8634 */ /* Contributed by Glen Nakamura <glen@imodulo.com> */ extern void abort (void); struct foo { char a, b, c, d, e, f, g, h, i, j; }; int test1 () { const char X[8] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H' }; char buffer[8]; __builtin_memcpy (buffer, X, 8); if (buffer[0] != 'A' || buffer[1] != 'B' || buffer[2] != 'C' || buffer[3] != 'D' || buffer[4] != 'E' || buffer[5] != 'F' || buffer[6] != 'G' || buffer[7] != 'H') abort (); return 0; } int test2 () { const char X[10] = { 'A', 'B', 'C', 'D', 'E' }; char buffer[10]; __builtin_memcpy (buffer, X, 10); if (buffer[0] != 'A' || buffer[1] != 'B' || buffer[2] != 'C' || buffer[3] != 'D' || buffer[4] != 'E' || buffer[5] != '\0' || buffer[6] != '\0' || buffer[7] != '\0' || buffer[8] != '\0' || buffer[9] != '\0') abort (); return 0; } int test3 () { const struct foo X = { a : 'A', c : 'C', e : 'E', g : 'G', i : 'I' }; char buffer[10]; __builtin_memcpy (buffer, &X, 10); if (buffer[0] != 'A' || buffer[1] != '\0' || buffer[2] != 'C' || buffer[3] != '\0' || buffer[4] != 'E' || buffer[5] != '\0' || buffer[6] != 'G' || buffer[7] != '\0' || buffer[8] != 'I' || buffer[9] != '\0') abort (); return 0; } int test4 () { const struct foo X = { .b = 'B', .d = 'D', .f = 'F', .h = 'H' , .j = 'J' }; char buffer[10]; __builtin_memcpy (buffer, &X, 10); if (buffer[0] != '\0' || buffer[1] != 'B' || buffer[2] != '\0' || buffer[3] != 'D' || buffer[4] != '\0' || buffer[5] != 'F' || buffer[6] != '\0' || buffer[7] != 'H' || buffer[8] != '\0' || buffer[9] != 'J') abort (); return 0; } int main () { test1 (); test2 (); test3 (); test4 (); return 0; } --wRRV7LY7NUeQGEoC--
From: Glen Nakamura <glen@imodulo.com> To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org Cc: Subject: Re: optimization/8634: [3.2 regression] incorrect code for inlining of memcpy under -O2 Date: Wed, 26 Mar 2003 10:36:20 -1000 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8634 Did this PR get changed by mistake? I'm still seeing this problem on the 3.3 branch as of 2003-03-26, but it's not marked as a 3.3 regression anymore... - glen
From: Steven Bosscher <s.bosscher@student.tudelft.nl> To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org, duchier@ps.uni-sb.de, gcc-prs@gcc.gnu.org, mark@codesourcery.com Cc: Subject: Re: optimization/8634: [3.2/3.3/3.4 regression] incorrect code for inlining of memcpy under -O2 Date: Sun, 06 Apr 2003 17:29:20 +0200 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8634 Thanks to Sherlock Hubicka, this patch by Zdenek has re-surfaced: http://gcc.gnu.org/ml/gcc-patches/2003-02/msg01655.html The message was probably ignored because of the inspired subject line: "[PATCH] ..." (sic). Greetz Steven
State-Changed-From-To: analyzed->closed State-Changed-Why: http://gcc.gnu.org/ml/gcc-patches/2003-04/msg00482.html http://gcc.gnu.org/ml/gcc-patches/2003-04/msg00489.html