[Bug middle-end/58746] New: Incorrect warning with -Waggressive-loop-optimizations

[Bug middle-end/58746] New: Incorrect warning with -Waggressive-loop-optimizations

[Joost.VandeVondele at mat dot ethz.ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58746

            Bug ID: 58746
           Summary: Incorrect warning with -Waggressive-loop-optimizations
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Joost.VandeVondele at mat dot ethz.ch

Only when compiled with LTO, the following testcase yields:

 gfortran  -flto=jobserver -use-linker-plugin -O2 -g -ffree-form test.f90 
test.f90: In function ‘expint.constprop’:
test.f90:43:0: warning: iteration 2147483646 invokes undefined behavior
[-Waggressive-loop-optimizations]
         DO ii=1,nm1
 ^
test.f90:43:0: note: containing loop

However, nm1 is clearly 0, by inspection of the code and as the write statement
at runtime illustrates:
 nm1=           0

> cat test.f90 
MODULE mathlib
  IMPLICIT NONE
  INTEGER, PARAMETER :: dp = SELECTED_REAL_KIND ( 14, 200 )
  INTEGER, PARAMETER :: maxfac = 30
  REAL(KIND=dp), PARAMETER, DIMENSION (0:maxfac) :: fac = 1
  CHARACTER(len=*), PARAMETER, PRIVATE :: moduleN = 'mathlib'
CONTAINS
  FUNCTION expint(n,x)
    INTEGER                                  :: n
    REAL(dp)                                 :: x, expint

    CHARACTER(len=*), PARAMETER :: routineN = 'expint', &
      routineP = moduleN//':'//routineN
    INTEGER, PARAMETER                       :: maxit = 100
    REAL(dp), PARAMETER :: eps = 6.e-14_dp, &
      euler = 0.5772156649015328606065120_dp, fpmin = TINY(0.0_dp)

    INTEGER                                  :: i, ii, nm1
    REAL(dp)                                 :: del, fact, h, psi

    nm1=n-1
    write(6,*) "nm1=",nm1

    expint=-LOG(x)-euler
    fact=1.0_dp
    DO i=1,MAXIT
      fact=-fact*x/i
      IF(i.NE.nm1) THEN
        del=-fact/(i-nm1)
      ELSE
        psi=-euler 
        DO ii=1,nm1
          psi=psi+1.0_dp/ii
        END DO
        del=fact*(-LOG(x)+psi)
      END IF
      expint=expint+del
      IF(ABS(del).LT.ABS(expint)*EPS) RETURN
    END DO

  END FUNCTION expint
END MODULE
USE  mathlib
REAL(KIND=dp), VOLATILE :: r=0.1_dp
r = expint(1,r)
END
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From: "rian.gabriel at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/58747] New: new_for
Date: Wed, 16 Oct 2013 12:48:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idX747

            Bug ID: 58747
           Summary: new_for
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rian.gabriel at gmail dot com

Sorry if it has already been reported.

The code compiles and runs without warning.

int i = 0;

for(int i : v)
{
   ...
}

[Bug middle-end/58746] [4.9 Regression] Incorrect warning with -Waggressive-loop-optimizations

[Joost.VandeVondele at mat dot ethz.ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58746

--- Comment #1 from Joost VandeVondele <Joost.VandeVondele at mat dot ethz.ch> ---
Reduced :

MODULE mathlib
  INTEGER, PARAMETER :: dp = 8
CONTAINS
  FUNCTION expint(n,x)
    REAL(dp) :: x, expint
    nm1=n-1
    DO i=1,MAXIT
      IF(i.NE.nm1) THEN
        DO ii=1,nm1
          psi=psi+1.0_dp/ii
        END DO
        del=fact*(-LOG(x)+psi)
      END IF
      expint=expint+del
    END DO
  END FUNCTION expint
END MODULE
USE  mathlib
REAL(KIND=dp), VOLATILE :: r=0.1_dp
r = expint(1,r)
END

[Bug middle-end/58746] [4.9 Regression] Incorrect warning with -Waggressive-loop-optimizations

[Joost.VandeVondele at mat dot ethz.ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58746

--- Comment #2 from Joost VandeVondele <Joost.VandeVondele at mat dot ethz.ch> ---
this testcase gives the same error without LTO. Just -O2 is sufficient:

  INTEGER, PARAMETER :: dp = 8
  REAL(KIND=dp), VOLATILE :: r=0.1_dp
  r = expint(1,r)
CONTAINS
  FUNCTION expint(n,x)
    REAL(dp) :: x, expint
    INTEGER :: maxit=100 
    nm1=n-1
    DO i=1,MAXIT
      IF(i.NE.nm1) THEN
        DO ii=1,nm1
          psi=psi+1.0_dp/ii
        END DO
        del=fact*(-LOG(x)+psi)
      END IF
      expint=expint+del
    END DO
  END FUNCTION expint
END

[Bug middle-end/58746] [4.9 Regression] Incorrect warning with -Waggressive-loop-optimizations

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58746

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.9.0

[Bug middle-end/58746] [4.9 Regression] Incorrect warning with -Waggressive-loop-optimizations

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58746

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1

[Bug middle-end/58746] [4.9 Regression] Incorrect warning with -Waggressive-loop-optimizations

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58746

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|2013-11-27 00:00:00         |2013-12-20
     Ever confirmed|0                           |1

--- Comment #3 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
I can confirm the warning for comment 2 only. The other two tests compile
without warning on x86_64-apple-darwin13 (-fuse-linker-plugin is not
supported).

Likely a duplicate of pr57904.

[Bug middle-end/58746] [4.9 Regression] Incorrect warning with -Waggressive-loop-optimizations

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58746

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #4 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Fixed by the patch in pr57904 comment 9. Marked as duplicate.

*** This bug has been marked as a duplicate of bug 57904 ***

[Bug middle-end/58746] [4.9 Regression] Incorrect warning with -Waggressive-loop-optimizations

[law at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58746

Bug 58746 depends on bug 57904, which changed state.

Bug 57904 Summary: [4.9 Regression] Bogus(?) "invokes undefined behavior" warning with Fortran's finalization wrapper (gfortran.dg/class_48.f90)
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57904

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED