re PR fortran/68829 (Segfaults with -Ofast due to large array on stack)

2017-08-07  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/68829
	* doc/invoke.texi: Document change in behvaior for -Ofast for
	Fortran.

2017-08-07  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/68829
	PR fortran/81701
	* options.c: Make -Ofast honor -fmax-stack-var-size.
	* invoke.texi: Document change.

2017-08-07  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/68829
	PR fortran/81701
	* gfortran.dg/o_fast_stacksize.90:  New test.

From-SVN: r250923

gcc/ChangeLog

+2017-08-07  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	PR fortran/68829
+	* doc/invoke.texi: Document change in behvaior for -Ofast for
+	Fortran.
+
 2017-08-07  Wilco Dijkstra  <wdijkstr@arm.com>
 
 	* config/aarch64/aarch64.c (aarch64_pushwb_single_reg):

gcc/doc/invoke.texi

@@ -7278,7 +7278,8 @@ Disregard strict standards compliance.  @option{-Ofast} enables all
 @option{-O3} optimizations.  It also enables optimizations that are not
 valid for all standard-compliant programs.
 It turns on @option{-ffast-math} and the Fortran-specific
-@option{-fno-protect-parens} and @option{-fstack-arrays}.
+@option{-fstack-arrays}, unless @option{-fmax-stack-var-size} is
+specified, and @option{-fno-protect-parens}.
 
 @item -Og
 @opindex Og

gcc/fortran/ChangeLog

+2017-08-07  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	PR fortran/68829
+	PR fortran/81701
+	* options.c: Make -Ofast honor -fmax-stack-var-size.
+	* invoke.texi: Document change.
+
 2017-08-01  Thomas König  <tkoenig@gcc.gnu.org>
 
 	PR fortran/79312

gcc/fortran/options.c

@@ -235,7 +235,9 @@ gfc_post_options (const char **pfilename)
   if (flag_protect_parens == -1)
     flag_protect_parens = !optimize_fast;
 
-  if (flag_stack_arrays == -1)
+  /* -Ofast sets implies -fstack-arrays unless an explicit size is set for
+     stack arrays.  */
+  if (flag_stack_arrays == -1 && flag_max_stack_var_size == -2)
     flag_stack_arrays = optimize_fast;
 
   /* By default, disable (re)allocation during assignment for -std=f95,
@@ -380,6 +382,10 @@ gfc_post_options (const char **pfilename)
       flag_max_stack_var_size = -1;
     }
 
+  /* Set flag_stack_arrays correctly.  */
+  if (flag_stack_arrays == -1)
+    flag_stack_arrays = 0;
+
   /* Set default.  */
   if (flag_max_stack_var_size == -2)
     flag_max_stack_var_size = 32768;

gcc/testsuite/ChangeLog

+2017-08-07  Thomas Koenig  <tkoenig@gcc.gnu.org>
+
+	PR fortran/68829
+	PR fortran/81701
+	* gfortran.dg/o_fast_stacksize.90:  New test.
+
 2017-08-07  Wilco Dijkstra  <wdijkstr@arm.com>
 
 	PR middle-end/46932

gcc/testsuite/gfortran.dg/o_fast_stacksize.f90

+! { dg-do compile }
+! { dg-options "-Ofast -fmax-stack-var-size=100 -fdump-tree-original" }
+MODULE foo
+CONTAINS
+  SUBROUTINE mysum(a)
+    INTEGER :: a(:)
+    WRITE(6,*) SUM(a)
+  END SUBROUTINE
+END MODULE foo
+
+USE foo
+INTEGER, ALLOCATABLE :: a(:)
+INTEGER, PARAMETER :: N=2**26 ! 256Mb array
+ALLOCATE(a(N)) ; a=1
+CALL mysum(a*a)
+END
+! { dg-final { scan-tree-dump-times "__builtin_malloc" 2 "original" } }