| Summary: | [3.3/3.4 Regression] [strength-reduce] -O2 optimalization produces wrong code | ||
|---|---|---|---|
| Product: | gcc | Reporter: | samal <samal> |
| Component: | rtl-optimization | Assignee: | Eric Botcazou <ebotcazou> |
| Status: | RESOLVED FIXED | ||
| Severity: | critical | CC: | gcc-bugs |
| Priority: | P1 | Keywords: | wrong-code |
| Version: | 3.0.4 | ||
| Target Milestone: | 3.3.1 | ||
| Host: | i386-pc-linux-gnu | Target: | i?86-*-* powerpc-*-* |
| Build: | i386-pc-linux-gnu | Known to work: | |
| Known to fail: | Last reconfirmed: | 2003-07-16 02:17:44 | |
Fix: Compile without optimization or with version 2.95 ... ;-) I can confirm this on i686-pc-linux with gcc 3.0.4, 3.3.1 (20030707), the mainline
(20030714) but it did not produce bad code with 2.95.3. I can also confirm this on
powerpc-apple-darwin6.6 (mainline 20030715) so it looks to be strength reduce bug
because if I use -fno-strength-reduce, I get the correct result. I also get bad code with the
mainline (20030715) on i686-unknown-openbsd3.1.
The code looks valid to me, no pointers at all so this is not the aliasing problem that the
other strength-reduce problems are about.
Here is the diff for powerpc with temp.s being the correct code (-O2 -fno-strength-reduce),
t.s (-O2):
--- t.s Tue Jul 15 22:15:53 2003
+++ temp.s Tue Jul 15 22:15:55 2003
@@ -23,17 +23,19 @@
stwu r1,-80(r1)
L12:
mr r30,r28
- li r29,2
+L11:
addi r28,r28,1
-L19:
+ li r29,0
+L9:
addi r30,r30,1
addis r3,r31,ha16(LC0-"L00000000001$pb")
la r3,lo16(LC0-"L00000000001$pb")(r3)
+ addi r29,r29,1
mr r4,r28
mr r5,r30
bl L_printf$stub
- addic. r29,r29,-1
- bge+ cr0,L19
+ cmpwi cr7,r29,2
+ ble+ cr7,L9
addis r3,r31,ha16(LC1-"L00000000001$pb")
mr r4,r28
la r3,lo16(LC1-"L00000000001$pb")(r3)
@@ -41,6 +43,8 @@
bl L_printf$stub
cmpwi cr7,r30,10
bgt- cr7,L1
+ cmpw cr7,r28,r30
+ ble+ cr7,L11
addis r3,r31,ha16(LC2-"L00000000001$pb")
mr r4,r28
la r3,lo16(LC2-"L00000000001$pb")(r3)
Here is a testcase suited for the testsuite:
void f(char*,int,int) __attribute__((__noinline__));
void f(char *t,int i,int j){if(t[0]=='C')abort();}
int main()
{
int i;
int first= 0;
int last= 0;
while (last<3) {
last = first;
while(first<=last) {
first++;
for (i=0;i<3;i++){
last++;
f("A",first,last);
}
if (last>10) return 0;
f("B",first,last);
}
f("C",first,last);
}
return 0;
}
Investigating. Subject: Bug 11536 CVSROOT: /cvs/gcc Module name: gcc Changes by: mmitchel@gcc.gnu.org 2003-07-21 16:52:38 Modified files: gcc : ChangeLog unroll.c gcc/testsuite : ChangeLog Added files: gcc/testsuite/gcc.dg: 20030721-1.c Log message: PR optimization/11536 * unroll.c (loop_iterations): Do not replace a register holding the final value by its equivalent before the loop if it is not invariant. PR optimization/11536 * gcc.dg/20030721-1.c: New test. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.579&r2=2.580 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/unroll.c.diff?cvsroot=gcc&r1=1.200&r2=1.201 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.2901&r2=1.2902 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/20030721-1.c.diff?cvsroot=gcc&r1=NONE&r2=1.1 Subject: Bug 11536 CVSROOT: /cvs/gcc Module name: gcc Branch: gcc-3_3-branch Changes by: mmitchel@gcc.gnu.org 2003-07-21 17:50:05 Modified files: gcc : ChangeLog unroll.c gcc/testsuite : ChangeLog Added files: gcc/testsuite/gcc.dg: 20030721-1.c Log message: PR optimization/11536 * unroll.c (loop_iterations): Do not replace a register holding the final value by its equivalent before the loop if it is not invariant. PR optimization/11536 * gcc.dg/20030721-1.c: New test. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=1.16114.2.678&r2=1.16114.2.679 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/unroll.c.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=1.184.2.4&r2=1.184.2.5 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=1.2261.2.239&r2=1.2261.2.240 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/20030721-1.c.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=NONE&r2=1.1.2.1 Fixed in GCC 3.3.1 and GCC 3.4. |
On the following code, gcc (version 3.0 or 3.3) with -O2 (or higer) produces wrong code from a very short program ... Environment: System: Linux camelot 2.4.19 #1 Fri Aug 16 17:01:16 CEST 2002 i686 unknown Architecture: i686 host: i386-pc-linux-gnu build: i386-pc-linux-gnu target: i386-pc-linux-gnu configured with: ../src/configure -v --enable-languages=c,c++,java,f77,proto,objc --prefix=/usr --infodir=/share/info --mandir=/share/man --enable-shared --with-gnu-as --with-gnu-ld --with-system-zlib --enable-long-long --enable-nls --without-included-gettext --disable-checking --enable-threads=posix --enable-java-gc=boehm --with-cpp-install-dir=bin --enable-objc-gc i386-linux How-To-Repeat: gcc -O2 the_following_file /* bug in gcc -O2 Reading specs from /usr/lib/gcc-lib/i386-linux/3.0.4/specs Configured with: ../src/configure -v --enable-languages=c,c++,java,f77,proto,objc --prefix=/usr --infodir=/share/info --mandir=/share/man --enable-shared --with-gnu-as --with-gnu-ld --with-system-zlib --enable-long-long --enable-nls --without-included-gettext --disable-checking --enable-threads=posix --enable-java-gc=boehm --with-cpp-install-dir=bin --enable-objc-gc i386-linux Thread model: posix gcc version 3.0.4 The same problem at another machine Reading specs from /usr/lib/gcc-lib/i386-linux/3.3/specs Configured with: ../src/configure -v --enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-gxx-include-dir=/usr/include/c++/3.3 --enable-shared --with-system-zlib --enable-nls --without-included-gettext --enable-__cxa_atexit --enable-clocale=gnu --enable-debug --enable-java-gc=boehm --enable-java-awt=xlib --enable-objc-gc i386-linux Thread model: posix gcc version 3.3 (Debian) **************** When compiled without optimalization, the program behaves correctly, it is it print lines upto "B f=4, l=12". However, when compiled with -O2, it finishes with " A f=1, l=3", when the inner while cycle condition is still satisfied ... Maybe the two while-cycles are somehow mixed up? */ int main() { int i; int first= 0; int last= 0; while (last<3) { last = first; while(first<=last) { first++; for (i=0;i<3;i++){ last++; printf("C f=%d, l=%d\n",first,last); } printf("B f=%d, l=%d\n",first,last); if (last>10) return 0; } printf(" A f=%d, l=%d\n",first,last); } return 0; }