[gcc r11-6687] PR fortran/93340 - fix missed substring simplifications

[Harald Anlauf <anlauf@gcc.gnu.org>]

https://gcc.gnu.org/g:bdd1b1f55529da00b867ef05a53a08fbfc3d1c2e

commit r11-6687-gbdd1b1f55529da00b867ef05a53a08fbfc3d1c2e
Author: Harald Anlauf <anlauf@gmx.de>
Date:   Thu Jan 14 20:25:33 2021 +0100

    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.

Diff:
---
 gcc/fortran/gfortran.h      |  1 +
 gcc/fortran/primary.c       | 55 +++++++++++++++++++++++++++++++++++++++++++++
 gcc/fortran/resolve.c       |  6 ++---
 gcc/testsuite/substr_10.f90 | 11 +++++++++
 gcc/testsuite/substr_9.f90  | 28 +++++++++++++++++++++++
 5 files changed, 98 insertions(+), 3 deletions(-)

diff --git a/gcc/fortran/gfortran.h b/gcc/fortran/gfortran.h
index 6585e4f3ecd..4dd72b620c9 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 db9ecf9a4f6..d0610d02ebd 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 ab7ffc2c8b6..bb069efef03 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 00000000000..918ca8af162
--- /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 00000000000..73152d6627f
--- /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" } }