From: Thomas Koenig <tkoenig@gcc.gnu.org>
Date: Tue, 6 Jul 2021 05:04:09 +0000 (+0200)
Subject: Do not replace variable op variable in I/O implied DO loop replacement.
X-Git-Tag: basepoints/gcc-13~6266
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d7e3855d5dd8c001bb65dc7da1cda0249bfc2986;p=thirdparty%2Fgcc.git

Do not replace variable op variable in I/O implied DO loop replacement.

This PR came about because index expressions of the form k+k in
implied DO loops in I/O statements were considered for replacement
by array slices.

Fixed by only doing the transformation if the expression is of the
type expr OP contastant.

gcc/fortran/ChangeLog:

	PR fortran/100227
	* frontend-passes.c (traverse_io_block): Adjust test for
	when a variable is eligible for the transformation to
	array slice.

gcc/testsuite/ChangeLog:

	PR fortran/100227
	* gfortran.dg/implied_do_io_7.f90: New test.
---

diff --git a/gcc/fortran/frontend-passes.c b/gcc/fortran/frontend-passes.c
index 72a4e0410b1c..996dcc2e5474 100644
--- a/gcc/fortran/frontend-passes.c
+++ b/gcc/fortran/frontend-passes.c
@@ -1299,8 +1299,8 @@ traverse_io_block (gfc_code *code, bool *has_reached, gfc_code *prev)
 		std::swap (start->value.op.op1, start->value.op.op2);
 	      gcc_fallthrough ();
 	    case INTRINSIC_MINUS:
-	      if ((start->value.op.op1->expr_type!= EXPR_VARIABLE
-		   && start->value.op.op2->expr_type != EXPR_CONSTANT)
+	      if (start->value.op.op1->expr_type!= EXPR_VARIABLE
+		  || start->value.op.op2->expr_type != EXPR_CONSTANT
 		  || start->value.op.op1->ref)
 		return false;
 	      if (!stack_top || !stack_top->iter
diff --git a/gcc/testsuite/gfortran.dg/implied_do_io_7.f90 b/gcc/testsuite/gfortran.dg/implied_do_io_7.f90
new file mode 100644
index 000000000000..63927aafea93
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/implied_do_io_7.f90
@@ -0,0 +1,16 @@
+! { dg-do run }
+! PR 100227 - this was falsely optimized, leading to nonsense  results.
+! Original test case by "Mathieu".
+
+program p
+  implicit none
+  integer, parameter :: nbmode = 3
+  integer :: k
+  real    :: mass(nbmode*2)
+  character (len=80) :: line
+  do k = 1, nbmode*2
+     mass(k) = k
+  end do
+  write (unit=line,fmt='(*(F6.2))') (mass(k+k), k=1,nbmode)
+  if (line /= '  2.00  4.00  6.00') stop 1
+end program