PR fortran/93340 - fix missed substring simplifications

Substrings were not reduced early enough for use in initializations,
such as DATA statements.  Add an early simplification for substrings
with constant starting and ending points.

gcc/fortran/ChangeLog:

	* gfortran.h (gfc_resolve_substring): Add prototype.
	* primary.c (match_string_constant): Simplify substrings with
	constant starting and ending points.
	* resolve.c: Rename resolve_substring to gfc_resolve_substring.
	(gfc_resolve_ref): Use renamed function gfc_resolve_substring.

gcc/testsuite/ChangeLog:

	* substr_10.f90: New test.
	* substr_9.f90: New test.

5 files changed, 98 insertions, 3 deletions

diff --git a/gcc/fortran/gfortran.h b/gcc/fortran/gfortran.h
index 6585e4f..4dd72b6 100644
--- a/gcc/fortran/gfortran.h
+++ b/gcc/fortran/gfortran.h
@@ -3467,6 +3467,7 @@ bool find_forall_index (gfc_expr *, gfc_symbol *, int);
 bool gfc_resolve_index (gfc_expr *, int);
 bool gfc_resolve_dim_arg (gfc_expr *);
 bool gfc_is_formal_arg (void);
+bool gfc_resolve_substring (gfc_ref *, bool *);
 void gfc_resolve_substring_charlen (gfc_expr *);
 match gfc_iso_c_sub_interface(gfc_code *, gfc_symbol *);
 gfc_expr *gfc_expr_to_initialize (gfc_expr *);
diff --git a/gcc/fortran/primary.c b/gcc/fortran/primary.c
index db9ecf9..d0610d0 100644
--- a/gcc/fortran/primary.c
+++ b/gcc/fortran/primary.c
@@ -1190,6 +1190,61 @@ got_delim:
   if (match_substring (NULL, 0, &e->ref, false) != MATCH_NO)
     e->expr_type = EXPR_SUBSTRING;
 
+  /* Substrings with constant starting and ending points are eligible as
+     designators (F2018, section 9.1).  Simplify substrings to make them usable
+     e.g. in data statements.  */
+  if (e->expr_type == EXPR_SUBSTRING
+      && e->ref && e->ref->type == REF_SUBSTRING
+      && e->ref->u.ss.start->expr_type == EXPR_CONSTANT
+      && (e->ref->u.ss.end == NULL
+	  || e->ref->u.ss.end->expr_type == EXPR_CONSTANT))
+    {
+      gfc_expr *res;
+      ptrdiff_t istart, iend;
+      size_t length;
+      bool equal_length = false;
+
+      /* Basic checks on substring starting and ending indices.  */
+      if (!gfc_resolve_substring (e->ref, &equal_length))
+	return MATCH_ERROR;
+
+      length = e->value.character.length;
+      istart = gfc_mpz_get_hwi (e->ref->u.ss.start->value.integer);
+      if (e->ref->u.ss.end == NULL)
+	iend = length;
+      else
+	iend = gfc_mpz_get_hwi (e->ref->u.ss.end->value.integer);
+
+      if (istart <= iend)
+	{
+	  if (istart < 1)
+	    {
+	      gfc_error ("Substring start index (%ld) at %L below 1",
+			 (long) istart, &e->ref->u.ss.start->where);
+	      return MATCH_ERROR;
+	    }
+	  if (iend > (ssize_t) length)
+	    {
+	      gfc_error ("Substring end index (%ld) at %L exceeds string "
+			 "length", (long) iend, &e->ref->u.ss.end->where);
+	      return MATCH_ERROR;
+	    }
+	  length = iend - istart + 1;
+	}
+      else
+	length = 0;
+
+      res = gfc_get_constant_expr (BT_CHARACTER, e->ts.kind, &e->where);
+      res->value.character.string = gfc_get_wide_string (length + 1);
+      res->value.character.length = length;
+      if (length > 0)
+	memcpy (res->value.character.string,
+		&e->value.character.string[istart - 1],
+		length * sizeof (gfc_char_t));
+      res->value.character.string[length] = '\0';
+      e = res;
+    }
+
   *result = e;
 
   return MATCH_YES;
diff --git a/gcc/fortran/resolve.c b/gcc/fortran/resolve.c
index ab7ffc2..bb069ef 100644
--- a/gcc/fortran/resolve.c
+++ b/gcc/fortran/resolve.c
@@ -5068,8 +5068,8 @@ resolve_array_ref (gfc_array_ref *ar)
 }
 
 
-static bool
-resolve_substring (gfc_ref *ref, bool *equal_length)
+bool
+gfc_resolve_substring (gfc_ref *ref, bool *equal_length)
 {
   int k = gfc_validate_kind (BT_INTEGER, gfc_charlen_int_kind, false);
 
@@ -5277,7 +5277,7 @@ gfc_resolve_ref (gfc_expr *expr)
 
       case REF_SUBSTRING:
 	equal_length = false;
-	if (!resolve_substring (*prev, &equal_length))
+	if (!gfc_resolve_substring (*prev, &equal_length))
 	  return false;
 
 	if (expr->expr_type != EXPR_SUBSTRING && equal_length)
diff --git a/gcc/testsuite/substr_10.f90 b/gcc/testsuite/substr_10.f90
new file mode 100644
index 0000000..918ca8a
--- /dev/null
+++ b/gcc/testsuite/substr_10.f90
@@ -0,0 +1,11 @@
+! { dg-do compile }
+! PR93340 - test error handling of substring simplification
+
+subroutine p
+  integer,parameter :: k = len ('a'(:0))
+  integer,parameter :: m = len ('a'(0:)) ! { dg-error "Substring start index" }
+  call foo ('bcd'(-8:-9))
+  call foo ('bcd'(-9:-8)) ! { dg-error "Substring start index" }
+  call foo ('bcd'(:12))   ! { dg-error "Substring end index" }
+  call foo ('bcd'(-12:))  ! { dg-error "Substring start index" }
+end
diff --git a/gcc/testsuite/substr_9.f90 b/gcc/testsuite/substr_9.f90
new file mode 100644
index 0000000..73152d6
--- /dev/null
+++ b/gcc/testsuite/substr_9.f90
@@ -0,0 +1,28 @@
+! { dg-do run }
+! { dg-options "-std=gnu -fdump-tree-original" }
+! PR93340 - issues with substrings in initializers
+
+program p
+  implicit none
+  integer, parameter :: m = 1
+  character b(2) /'a', 'b'   (1:1)/
+  character c(2) /'a', 'bc'  (1:1)/
+  character d(2) /'a', 'bxyz'(m:m)/
+  character e(2)
+  character f(2)
+  data e /'a', 'bxyz'( :1)/
+  data f /'a', 'xyzb'(4:4)/
+  character :: g(2) = [ 'a', 'b' (1:1) ]
+  character :: h(2) = [ 'a', 'bc'(1:1) ]
+  character :: k(2) = [ 'a', 'bc'(m:1) ]
+  if (b(2) /= "b") stop 1
+  if (c(2) /= "b") stop 2
+  if (d(2) /= "b") stop 3
+  if (e(2) /= "b") stop 4
+  if (f(2) /= "b") stop 5
+  if (g(2) /= "b") stop 6
+  if (h(2) /= "b") stop 7
+  if (k(2) /= "b") stop 8
+end
+
+! { dg-final { scan-tree-dump-times "xyz" 0 "original" } }