[PATCH] Fortran: handle explicit-shape specs with constant bounds [PR105954]

[Harald Anlauf <anlauf@gmx.de>]

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Dear all,

after simplification of constant bound expressions of an explicit
shape spec of an array, we need to ensure that we never obtain
negative extents.  In some cases this did happen, and we ICEd
as we hit an assert that this should never happen...

The original testcase by Gerhard exhibited this for sizeof()
of a derived type with an array component, but the issue is
more fundamental and affects other intrinsics during
simplification.

A straightforward solution "fixes up" the upper bound in the
shape spec when it is known to be below lower bounds minus one.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

Thanks,
Harald


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From 65f7fd793415cb291ffb5bca8cdbcb10fc511ab8 Mon Sep 17 00:00:00 2001
From: Harald Anlauf <anlauf@gmx.de>
Date: Mon, 20 Jun 2022 20:59:55 +0200
Subject: [PATCH] Fortran: handle explicit-shape specs with constant bounds
 [PR105954]

gcc/fortran/ChangeLog:

	PR fortran/105954
	* decl.cc (variable_decl): Adjust upper bounds for explicit-shape
	specs with constant bound expressions to ensure non-negative
	extents.

gcc/testsuite/ChangeLog:

	PR fortran/105954
	* gfortran.dg/pr105954.f90: New test.
---
 gcc/fortran/decl.cc                    | 12 ++++++++++++
 gcc/testsuite/gfortran.dg/pr105954.f90 | 26 ++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)
 create mode 100644 gcc/testsuite/gfortran.dg/pr105954.f90

diff --git a/gcc/fortran/decl.cc b/gcc/fortran/decl.cc
index bd586e75008..26ff54d4684 100644
--- a/gcc/fortran/decl.cc
+++ b/gcc/fortran/decl.cc
@@ -2775,6 +2775,18 @@ variable_decl (int elem)
 		  else
 		    gfc_free_expr (n);
 		}
+	      /* For an explicit-shape spec with constant bounds, ensure
+		 that the effective upper bound is not lower than the
+		 respective lower bound minus one.  Otherwise adjust it so
+		 that the extent is trivially derived to be zero.  */
+	      if (as->lower[i]->expr_type == EXPR_CONSTANT
+		  && as->upper[i]->expr_type == EXPR_CONSTANT
+		  && as->lower[i]->ts.type == BT_INTEGER
+		  && as->upper[i]->ts.type == BT_INTEGER
+		  && mpz_cmp (as->upper[i]->value.integer,
+			      as->lower[i]->value.integer) < 0)
+		mpz_sub_ui (as->upper[i]->value.integer,
+			    as->lower[i]->value.integer, 1);
 	    }
 	}
     }
diff --git a/gcc/testsuite/gfortran.dg/pr105954.f90 b/gcc/testsuite/gfortran.dg/pr105954.f90
new file mode 100644
index 00000000000..89004bf9aa7
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr105954.f90
@@ -0,0 +1,26 @@
+! { dg-do compile }
+! { dg-options "-fdump-tree-original" }
+! PR fortran/105954 - ICE in gfc_element_size, at fortran/target-memory.cc:132
+! Contributed by G.Steinmetz
+
+program p
+  use iso_c_binding, only: c_float, c_sizeof
+  implicit none
+  integer, parameter :: n = -99
+  type t
+     real :: b(3,7:n)
+  end type
+  type, bind(c) :: u
+     real(c_float) :: b(3,7:n)
+  end type
+  type(t) :: d
+  type(u) :: e
+  integer, parameter :: k = storage_size(d)
+  integer, parameter :: m = sizeof(d)
+  integer, parameter :: l = c_sizeof(e)
+  if (k /= 0) stop 1
+  if (m /= 0) stop 2
+  if (l /= 0) stop 3
+end
+
+! { dg-final { scan-tree-dump-not "_gfortran_stop_numeric" "original" } }
--
2.35.3