This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Help with detection of an invariant


On S/390 the test case gcc.dg/loop-9.c currently fails:

  void f (double *a) 
  { 
    int i; 
    for (i = 0; i < 100; i++) 
      a[i] = 18.4242; 
  }

It seems to expect that moving 18.4242 to a register is moved out
of the loop, but on S/390 it isn't.  It turns out that
move_invariant_reg() is never called from move_invariants()
because the invariants vector is empty.  Now,
find_invariant_insn() checks the insn for invariants using
check_dependencies().

  (insn 29 28 30 3 (set (mem:DF (reg:DI 81 [ ivtmp.8 ]) [0 MEM[base: _15, offset: 0B]+0 S8 A64])
          (const_double:DF 1.84241999999999990222931955941021442413330078125e+1 [0x0.9364c2f837b4ap+5])) .../loop-9.c:9 918 {*movdf_64}
       (nil))

check_dependencies() comes across reg 81 first, decides that is
not an invariant and returns false so that find_invariant_insn()
never even looks at the constant.

Actually, the constant should be moved (from the literal pool) to
a floating point register (and actually is in the assembly
output), and that move could be moved out of the loop (it's not).
Where should I look for the root cause?

Ciao

Dominik ^_^  ^_^

-- 

Dominik Vogt
IBM Germany


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]