https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111427
Kewen Lin <linkw at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2023-09-26
Keywords|ra, wrong-code |testsuite-fail
Assignee|unassigned at gcc dot gnu.org |linkw at gcc dot gnu.org
CC| |linkw at gcc dot gnu.org
Ever confirmed|0 |1
Status|UNCONFIRMED |ASSIGNED
--- Comment #2 from Kewen Lin <linkw at gcc dot gnu.org> ---
I found it can be reproduced on Power8 but not on Power9 (BE since only BE
supports -m32).
The option can be reduced to:
opts="-m32 -funroll-loops -O2 -mcpu=power8"
Looking into the affected test case, IMHO this is a test issue:
subroutine foo(a,x,y,n)
implicit none
integer n,i
real*8 y(n),x(n),a
do i=1,n
a=a+x(i)*y(i)+x(i)
enddo
return
end
program test
real*8 x(1024),y(1024),a ===> line A
do i=1,1024
x(i) = i
y(i) = i+1
enddo
call foo(a,x,y,1024)
if (a.ne.359488000.0) STOP 1
end
The variable a in line A is an uninitialized variable.
Without the culprit commit, the address of the passed a is 0xfffeec30:
Dump of assembler code for function MAIN__:
0x100008b0 <+0>: stwu r1,-16416(r1)
...
0x100009f4 <+324>: lis r12,4096
0x100009f8 <+328>: addi r5,r1,16
0x100009fc <+332>: addi r4,r1,8208
0x10000a00 <+336>: addi r3,r1,16400
0x10000a04 <+340>: addi r6,r12,3160
=> 0x10000a08 <+344>: bl 0x10000620 <foo_>
(gdb) i r r3
r3 0xfffeec30 4294896688
(gdb) x /2x 0xfffeec30
0xfffeec30: 0x10000524 0x00000000
the random value of "a" is 0x1000052400000000, a tiny float value
(1.289846527864432e-231) and doesn't cause the comparison to fail.
With the culprit commit, the address of the passed a is 0xfffeec20:
100008b0 <MAIN__>:
100008b0: 94 21 bf d0 stwu r1,-16432(r1)
100008b4: 3d 20 10 00 lis r9,4096
...
(gdb) x /2x 0xfffeec20
0xfffeec20: 0xfffeec40 0x0fddd03c
(gdb) i r r3
r3 0xfffeec20 4294896672
the random value of "a" is 0xfffeec400fddd03c, which is NAN, so it causes the
comparison to fail.
I'm not sure why this doesn't get exposed before (so lucky), but an explicit
initialization for a should fix this.
