[Bug fortran/38111] New: unneeded temporary

[Bug fortran/38111] New: unneeded temporary

[jv244 at cam dot ac dot uk]

another case where an unneeded temp is created. Maybe not so easy to fix?

SUBROUTINE S1(a)
integer :: a(:),i,N
N=SIZE(a)
a=(/(I,I=1,N)/)
END SUBROUTINE


-- 
           Summary: unneeded temporary
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jv244 at cam dot ac dot uk
OtherBugsDependingO 36854
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38111

[Bug fortran/38111] unneeded temporary

[pault at gcc dot gnu dot org]

------- Comment #1 from pault at gcc dot gnu dot org  2008-11-18 19:57 -------
Joost,

Do you know of any compilers that catch this?  As you say, it is not so easy to
fix.

BTW you say that this another case where an unneeded temp is created.  I can
see your PRs after this.  Which ones come before?

Paul


-- 

pault at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-11-18 19:57:17
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38111

[Bug fortran/38111] unneeded temporary

[jv244 at cam dot ac dot uk]

------- Comment #2 from jv244 at cam dot ac dot uk  2008-11-19 13:18 -------
(In reply to comment #1)
> Do you know of any compilers that catch this?  As you say, it is not so easy to
> fix.

I believe ifort gets this right (compiled with 'ifort -S -heap-arrays 64), but
this is just looking at the assembly, which normally contains calls to
for_allocate if a temp is generated:

s1_:
# parameter 1: %rdi
..B1.1:                         # Preds ..B1.0
..___tag_value_s1_.1:                                           #1.12
        movq      48(%rdi), %rsi                                #4.1
        movl      $1, %r8d                                      #4.1
        testq     %rsi, %rsi                                    #4.1
        jle       ..B1.5        # Prob 10%                      #4.1
                                # LOE rbx rbp rsi rdi r8 r12 r13 r14 r15
..B1.2:                         # Preds ..B1.1
        movq      (%rdi), %rax                                  #4.1
        movq      56(%rdi), %rcx                                #4.1
        movq      %rcx, %rdx                                    #4.1
        subq      %rcx, %rax                                    #
                                # LOE rax rdx rcx rbx rbp rsi r8 r12 r13 r14
r15
..B1.3:                         # Preds ..B1.3 ..B1.2
        movl      %r8d, (%rdx,%rax)                             #4.1
        addq      %rcx, %rdx                                    #4.1
        addq      $1, %r8                                       #4.1
        cmpq      %rsi, %r8                                     #4.1
        jle       ..B1.3        # Prob 82%                      #4.1
                                # LOE rax rdx rcx rbx rbp rsi r8 r12 r13 r14
r15
..B1.5:                         # Preds ..B1.3 ..B1.1
        ret                                                     #5.1
        .align    2,0x90


> 
> BTW you say that this another case where an unneeded temp is created.  I can
> see your PRs after this.  Which ones come before?

I've added a number of these as blocking PR36854. As mentioned before, all
derived from CP2K. I believe these are relatively important to fix, the
performance inpact of generating an unneeded temp can be very large.

Joost

> 
> Paul
> 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38111

[Bug fortran/38111] unneeded temporary

[jv244 at cam dot ac dot uk]

------- Comment #3 from jv244 at cam dot ac dot uk  2010-04-27 18:07 -------
still fails with current trunk.


-- 

jv244 at cam dot ac dot uk changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.6.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38111

[Bug fortran/38111] unneeded temporary

[dfranke at gcc dot gnu dot org]

------- Comment #4 from dfranke at gcc dot gnu dot org  2010-05-09 20:49 -------
Enhancement only - and probably a dupe of PR33341?!


-- 

dfranke at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dfranke at gcc dot gnu dot
                   |                            |org
           Severity|normal                      |enhancement


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38111

[Bug fortran/38111] unneeded temporary

[tkoenig at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38111

Thomas Koenig <tkoenig at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tkoenig at gcc dot gnu.org

--- Comment #5 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
One way of handling this would be to create a DO loop
from the array assignment.

Of course, we would have to make sure check for dependencies,
for example

a = [(a(4)+3,i=1,n)]