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From: "toon at moene dot org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/51310] -finit-bla doesn't initialize *all* items of type bla to the requested constant.
Date: Mon, 05 Dec 2011 20:04:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D51310

--- Comment #3 from Toon Moene <toon at moene dot org> 2011-12-05 20:04:21 =
UTC ---
At first I thought that gfortran would initialize small local arrays to
whatever -finit-real indicated by making them static, instead of stack base=
d.

However, perusing the assembler output of

      subroutine sub
      real a(3)
      print*,a
      end

(as a diff between gfortran -S and gfortran -S -finit-real=3Dsnan):

17c17,27
<     movq    $.LC0, -536(%rbp)
---
> 	movl	$1, %eax
> .L3:
> 	cmpq	$3, %rax
> 	jg	.L2
> 	leaq	-1(%rax), %rdx
> 	movl	$0x7fa00000, %ecx
> 	movl	%ecx, -16(%rbp,%rdx,4)
> 	addq	$1, %rax
> 	jmp	.L3
> .L2:

and checking with a small main program

      call sub
      end

that the output is really different:

$ ./a.out
  1.12103877E-44   0.0000000      9.80908925E-45

vs:

$ ./a.out
             NaN             NaN             NaN

convinced me otherwise.

So one wonders why that doesn't work with variable length automatic arrays =
(or
why it would even be hard to initialize malloc'd automatic arrays /
allocatables).

This quest to be continued ("do you think coconuts migrate ?  No - but they
could be carried.").