[backport gcc-4.9/trunk r199350 <mikpe@it.uu.se>]

gcc/

2013-05-27  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/57396
	* tree-affine.c (double_int_constant_multiple_p): Properly
	return false for val == 0 and div != 0.

gcc/testsuite/

2013-05-27  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/57396
	* gfortran.fortran-torture/execute/pr57396.f90: New testcase.

--- gcc-4.8.1/gcc/testsuite/gfortran.fortran-torture/execute/pr57396.f90.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.8.1/gcc/testsuite/gfortran.fortran-torture/execute/pr57396.f90	2013-06-01 10:39:02.882165017 +0200
@@ -0,0 +1,33 @@
+module testmod
+  implicit none
+
+  contains
+
+  subroutine foo(n)
+    integer, intent(in) :: n
+    real :: r(0:n,-n:n), a(0:n,-n:n), dj
+    integer :: k, j
+
+    ! initialize with some dummy values
+    do j = -n, n
+      a(:, j) = j
+      r(:,j) = j + 1
+    end do
+
+    ! here be dragons
+    do k = 0, n
+      dj = r(k, k - 2) * a(k, k - 2)
+      r(k,k) = a(k, k - 1) * dj
+    enddo
+
+    if (r(0,0) .ne. -2.) call abort
+
+  end subroutine
+
+end module
+
+program test
+  use testmod
+  implicit none
+  call foo(5)
+end program
--- gcc-4.8.1/gcc/tree-affine.c.~1~	2013-01-10 21:38:27.000000000 +0100
+++ gcc-4.8.1/gcc/tree-affine.c	2013-06-01 10:39:02.882165017 +0200
@@ -736,11 +736,10 @@ free_affine_expand_cache (struct pointer
 }
 
 /* If VAL != CST * DIV for any constant CST, returns false.
-   Otherwise, if VAL != 0 (and hence CST != 0), and *MULT_SET is true,
-   additionally compares CST and MULT, and if they are different,
-   returns false.  Finally, if neither of these two cases occur,
-   true is returned, and if CST != 0, CST is stored to MULT and
-   MULT_SET is set to true.  */
+   Otherwise, if *MULT_SET is true, additionally compares CST and MULT,
+   and if they are different, returns false.  Finally, if neither of these
+   two cases occur, true is returned, and CST is stored to MULT and MULT_SET
+   is set to true.  */
 
 static bool
 double_int_constant_multiple_p (double_int val, double_int div,
@@ -749,7 +748,13 @@ double_int_constant_multiple_p (double_i
   double_int rem, cst;
 
   if (val.is_zero ())
-    return true;
+    {
+      if (*mult_set && !mult->is_zero ())
+	return false;
+      *mult_set = true;
+      *mult = double_int_zero;
+      return true;
+    }
 
   if (div.is_zero ())
     return false;