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Compile the code using "gcc -O2" and the program doesn't give any output. It works with "gcc -O1" and works with gcc 2.95. Release: 2.96 - 3.2 Environment: x86 Linux How-To-Repeat: compile using "gcc -O2" and run it
State-Changed-From-To: open->analyzed State-Changed-Why: Confirmed. Here's the same program, slightly modified: ------------------------ inline int tag() { return 0; } int main() { int i; for (i = 0; i < (tag() ? 2 : 1); i++) printf("Hello1\n"); } -------------------------- The loop should be executed at least once, but isn't when compiled with -O2 on 3.2, 3.3 and mainline. It worked with 2.95, though, so this is a regression. A serious one, I'd say. W.
State-Changed-From-To: analyzed->open State-Changed-Why: x
State-Changed-From-To: open->analyzed State-Changed-Why: This is a bug in loop unrolling; 2.95 shows the bug with -funroll-loops. The only difference is that now we do some unrolling at -O2. The loop optimizer properly calculates that there will always be a single pass through the loop. The unroller has a special case for this. It looks for and deletes an unconditional jump to the continue point, then deletes a conditional jump from the end of the loop. Unfortunately, this code fails to handle nontrivial for loops, as the unconditional jump at the beginning of the loop (created previously by loop inversion) is to the test, not to the continue point. So that jump is not deleted, but the conditional jump at the end is, and so we just skip over the loop. Oops.
From: Jason Merrill <jason@redhat.com> To: Steven Bosscher <s.bosscher@student.tudelft.nl> Cc: gcc-gnats@gcc.gnu.org, mchen@vmware.com, gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org, gcc-prs@gcc.gnu.org, agesen@vmware.com, mendel@vmware.com Subject: Re: optimization/10171: [3.2/3.3/3.4 regression] wrong code for inlined function Date: Fri, 21 Mar 2003 18:45:52 -0500 On Sat, 22 Mar 2003 00:33:02 +0100, Steven Bosscher <s.bosscher@student.tudelft.nl> wrote: > From your analysis, I would suspect that this PR is a duplicate > of high-priority PR opt/8414. Is there any way to verify this? I don't think so; it doesn't look like the loop in 8414 only has a single iteration. Jason
From: Steven Bosscher <s.bosscher@student.tudelft.nl> To: gcc-gnats@gcc.gnu.org, mchen@vmware.com, gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org, gcc-prs@gcc.gnu.org, agesen@vmware.com, mendel@vmware.com, jason@gcc.gnu.org Cc: Subject: Re: optimization/10171: [3.2/3.3/3.4 regression] wrong code for inlined function Date: Sat, 22 Mar 2003 00:33:02 +0100 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10171 Jason, From your analysis, I would suspect that this PR is a duplicate of high-priority PR opt/8414. Is there any way to verify this? (Hoping you *do* have access to IA64 hardware ;-) Greetz Steven
From: Janis Johnson <janis187@us.ibm.com> To: gcc-gnats@gcc.gnu.org, mchen@vmware.com, gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org, gcc-prs@gcc.gnu.org, agesen@vmware.com, mendel@vmware.com Cc: Subject: Re: optimization/10171: [3.2/3.3/3.4 regression] wrong code for inlined function Date: Sat, 22 Mar 2003 13:40:07 -0800 Not that it's useful, but for i686-linux the regression appears with this patch: Wed Sep 1 21:13:48 1999 Richard Henderson <rth@cygnus.com> Merge new ia32 backend from the branch! * i386.h, i386.c, i386.md, reg-stack.c, i386/unix.h: Many changes. See ChangeLog.P2 on new_ia32_branch for details. * rtl.h (stack_regs_mentioned_p): Delete prototype. * i386/cygwin.h (SUBTARGET_PROLOGUE): No more do_rtl. * i386/win32.h (SUBTARGET_PROLOGUE): Likewise. * i386/gas.h (ASM_FILE_START): Define. * i386/winnt.c (i386_pe_valid_decl_attribute_p): Update for name change of ix86_valid_decl_attribute_p. (i386_pe_valid_type_attribute_p): Similarly. http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10171
From: Janis Johnson <janis187@us.ibm.com> To: Steven Bosscher <s.bosscher@student.tudelft.nl> Cc: gcc-gnats@gcc.gnu.org, mchen@vmware.com, gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org, gcc-prs@gcc.gnu.org, agesen@vmware.com, mendel@vmware.com, janis187@us.ibm.com Subject: Re: optimization/10171: [3.2/3.3/3.4 regression] wrong code for inlined function Date: Sat, 22 Mar 2003 15:01:50 -0800 On Sat, Mar 22, 2003 at 11:22:32PM +0100, Steven Bosscher wrote: > http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10171 > > Janis, > > If the patch you identified really breaks stuff, then this PR should be > in the > category "target", agree? Not necessarily; see Jason's comment about how -O2 does some unrolling. The identified patch might have merely made that change (as far as this problem is concerned).
From: Steven Bosscher <s.bosscher@student.tudelft.nl> To: gcc-gnats@gcc.gnu.org, mchen@vmware.com, gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org, gcc-prs@gcc.gnu.org, agesen@vmware.com, mendel@vmware.com, janis187@us.ibm.com Cc: Subject: Re: optimization/10171: [3.2/3.3/3.4 regression] wrong code for inlined function Date: Sat, 22 Mar 2003 23:22:32 +0100 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10171 Janis, If the patch you identified really breaks stuff, then this PR should be in the category "target", agree? Greetz Steven
From: jason@gcc.gnu.org To: gcc-gnats@gcc.gnu.org Cc: Subject: optimization/10171 Date: 25 Mar 2003 20:23:08 -0000 CVSROOT: /cvs/gcc Module name: gcc Branch: gcc-3_3-branch Changes by: jason@gcc.gnu.org 2003-03-25 20:23:08 Modified files: gcc : ChangeLog unroll.c Log message: PR optimization/10171 * unroll.c (unroll_loop): Don't delete the jump at the end unless we also delete a jump at the beginning. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=1.16114.2.362&r2=1.16114.2.363 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/unroll.c.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=1.184.2.1&r2=1.184.2.2
From: jason@gcc.gnu.org To: gcc-gnats@gcc.gnu.org Cc: Subject: optimization/10171 Date: 25 Mar 2003 20:23:28 -0000 CVSROOT: /cvs/gcc Module name: gcc Branch: gcc-3_2-branch Changes by: jason@gcc.gnu.org 2003-03-25 20:23:28 Modified files: gcc : ChangeLog unroll.c Log message: PR optimization/10171 * unroll.c (unroll_loop): Don't delete the jump at the end unless we also delete a jump at the beginning. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_2-branch&r1=1.13152.2.657.2.279&r2=1.13152.2.657.2.280 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/unroll.c.diff?cvsroot=gcc&only_with_tag=gcc-3_2-branch&r1=1.160.2.4.2.4&r2=1.160.2.4.2.5
From: jason@gcc.gnu.org To: gcc-gnats@gcc.gnu.org Cc: Subject: optimization/10171 Date: 25 Mar 2003 20:24:26 -0000 CVSROOT: /cvs/gcc Module name: gcc Changes by: jason@gcc.gnu.org 2003-03-25 20:24:26 Modified files: gcc : ChangeLog unroll.c Log message: PR optimization/10171 * unroll.c (unroll_loop): Don't delete the jump at the end unless we also delete a jump at the beginning. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=1.17214&r2=1.17215 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/unroll.c.diff?cvsroot=gcc&r1=1.189&r2=1.190
From: jason@gcc.gnu.org To: gcc-gnats@gcc.gnu.org Cc: Subject: optimization/10171 Date: 25 Mar 2003 20:24:42 -0000 CVSROOT: /cvs/gcc Module name: gcc Changes by: jason@gcc.gnu.org 2003-03-25 20:24:42 Added files: gcc/testsuite/gcc.dg: loop-2.c Log message: PR optimization/10171 * unroll.c (unroll_loop): Don't delete the jump at the end unless we also delete a jump at the beginning. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/loop-2.c.diff?cvsroot=gcc&r1=NONE&r2=1.1
Responsible-Changed-From-To: unassigned->jason Responsible-Changed-Why: x
State-Changed-From-To: analyzed->closed State-Changed-Why: fixed