[PATCH] PR 83705 Repeat with large values

[PATCH] PR 83705 Repeat with large values

[Janne Blomqvist]

This patch fixes the regression by increasing the limit where we fall
back to runtime to 2**28 elements, which is the same limit where
previous releases failed. The are still bugs in the runtime
evaluation, so in many cases longer characters will still fail, so
print a warning message.

Regtested on x86_64-pc-linux-gnu, Ok for trunk?

gcc/fortran/ChangeLog:

2018-01-31  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/83705
	* simplify.c (gfc_simplify_repeat): Increase limit for deferring
	to runtime, print a warning message.

gcc/testsuite/ChangeLog:

2018-01-31  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/83705
	* gfortran.dg/repeat_7.f90: Catch warning message.
---
 gcc/fortran/simplify.c                 | 12 ++++++++----
 gcc/testsuite/gfortran.dg/repeat_7.f90 |  2 +-
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/gcc/fortran/simplify.c b/gcc/fortran/simplify.c
index 2458956..324f858 100644
--- a/gcc/fortran/simplify.c
+++ b/gcc/fortran/simplify.c
@@ -6121,12 +6121,16 @@ gfc_simplify_repeat (gfc_expr *e, gfc_expr *n)
   len = e->value.character.length;
   gfc_charlen_t nlen = ncop * len;
 
-  /* Here's a semi-arbitrary limit. If the string is longer than 32 MB
-     (8 * 2**20 elements * 4 bytes (wide chars) per element) defer to
+  /* Here's a semi-arbitrary limit. If the string is longer than 1 GB
+     (2**28 elements * 4 bytes (wide chars) per element) defer to
      runtime instead of consuming (unbounded) memory and CPU at
      compile time.  */
-  if (nlen > 8388608)
-    return NULL;
+  if (nlen > 268435456)
+    {
+      gfc_warning_now (0, "Evaluation of string longer than 2**28 at %L"
+		       " deferred to runtime, expect bugs", &e->where);
+      return NULL;
+    }
 
   result = gfc_get_character_expr (e->ts.kind, &e->where, NULL, nlen);
   for (size_t i = 0; i < (size_t) ncop; i++)
diff --git a/gcc/testsuite/gfortran.dg/repeat_7.f90 b/gcc/testsuite/gfortran.dg/repeat_7.f90
index 82f8dbf..80a2506 100644
--- a/gcc/testsuite/gfortran.dg/repeat_7.f90
+++ b/gcc/testsuite/gfortran.dg/repeat_7.f90
@@ -4,5 +4,5 @@
 ! compile time.
 program p
   character, parameter :: z = 'z'
-  print *, repeat(z, huge(1_4))
+  print *, repeat(z, huge(1_4)) ! { dg-warning "Evaluation of string" }
 end program p
-- 
2.7.4

Re: [PATCH] PR 83705 Repeat with large values

[Steve Kargl]

On Wed, Jan 31, 2018 at 10:18:46PM +0200, Janne Blomqvist wrote:
> This patch fixes the regression by increasing the limit where we fall
> back to runtime to 2**28 elements, which is the same limit where
> previous releases failed. The are still bugs in the runtime
> evaluation, so in many cases longer characters will still fail, so
> print a warning message.
> 
> Regtested on x86_64-pc-linux-gnu, Ok for trunk?
> 

Yes.

-- 
Steve