http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47365
Summary: [4.5 Regression] wrong code with -O -ftree-pre
Product: gcc
Version: 4.5.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: zso...@seznam.cz
Host: x86_64-pc-linux-gnu
Target: x86_64-pc-linux-gnu
Created attachment 23035
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23035
reduced testcase
Reported by Vegard Nossum at IRC.
Output:
$ gcc-4.5 -O -ftree-pre testcase.c
$ ./a.out
Aborted
In the testcase.c.092t.pre dump, there is:
...
<bb 2>:
D.2739_4 = b.a[0].i;
i.0_5 = i;
if (D.2739_4 != i.0_5)
goto <bb 3>;
else
goto <bb 4>;
<bb 3>:
b.a[0] = b.a[1];
b.a[1].i = D.2739_4;
pretmp.3_6 = b.a[1].i;
goto <bb 6>;
<bb 4>:
...
<bb 9>:
<bb 6>:
# prephitmp.4_8 = PHI <D.2739_4(9), pretmp.3_6(3)>
D.2739_9 = prephitmp.4_8;
D.2739_9 = prephitmp.4_8;
if (D.2739_9 == 0)
goto <bb 7>;
...
Problematic line is
pretmp.3_6 = b.a[1].i;
which reads the new value of "b.a[1].i". It should either happen one line
earlier, or it should read "b.a[0].i".
It seems that the fact "b.a[0] = b.a[1]" overwrites "b.a[0].i" is ignored.
Of couse I can be wrong.
Tested revisions:
r169006 - OK
4.5 r168785 - fail
4.4 r168785 - OK
