https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63311
Bug ID: 63311
Summary: [4.9/5 Regression] -O1 optimization introduces
valgrind warning
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: Joost.VandeVondele at mat dot ethz.ch
The following testcase yields a valgrind error when compiled with -O1 but not
at -O0. 4.8 is fine 4.9/trunk is not.
> gfortran -O1 -g bug.f90 && valgrind ./a.out
==57092== Conditional jump or move depends on uninitialised value(s)
==57092== at 0x4006F5: __m1_MOD_test (bug.f90:20)
==57092== by 0x4007BB: main (bug.f90:36)
==57092== ERROR SUMMARY: 4 errors from 1 contexts (suppressed: 6 from 6)
> cat bug.f90
MODULE M1
IMPLICIT NONE
CONTAINS
INTEGER FUNCTION foo()
INTEGER, VOLATILE :: v=42
foo=v
END FUNCTION
SUBROUTINE test(n,flag)
INTEGER :: n,i,j,k,l,tt
LOGICAL :: flag
REAL(KIND=8) :: v,t
IF (flag) THEN
t=42
tt=foo()
ENDIF
v=0
DO i=1,n
v=0
IF (flag) THEN
IF (tt==i) v=MAX(v,t)
ENDIF
DO j=1,n
DO k=1,n
v=MAX(v,sin(REAL(j*k)))
ENDDO
ENDDO
ENDDO
END SUBROUTINE
END MODULE M1
USE M1
INTEGER :: n
LOGICAL :: flag
n=4
flag=.FALSE.
CALL test(n,flag)
END
what seems to happen is that '(tt==i)' is evaluated before IF (flag) is
evaluated, also in the case where 'flag==.FALSE.', while 'tt' is only
initialized in the .TRUE. case.
I actually think generated code might nevertheless be correct, but it makes
valgrind less useful on -O1 code.
