From 662de36bf798c8c470b382015283fe3a439cdd8f Mon Sep 17 00:00:00 2001
From: Thomas Koenig <tkoenig@gcc.gnu.org>
Date: Tue, 15 Dec 2020 17:10:37 +0100
Subject: [PATCH] Add the -fdebug-aux-vars flag to debug variables generated by
 Fortran.

gcc/fortran/ChangeLog:

	PR fortran/90207
	* invoke.texi: Document -fdebug-aux-vars.
	* lang.opt: Add -fdebug-aux-vars.
	* trans.c (MAX_PREFIX_LEN): New macro.
	(create_var_debug_raw): New function.
	(gfc_create_var_np): Call create_var_debug_raw if
	flag_debug_aux_vars is set.
---
 gcc/fortran/invoke.texi | 11 ++++++++++-
 gcc/fortran/lang.opt    |  4 ++++
 gcc/fortran/trans.c     | 42 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi
index 8bdc8a6b038..069ccd339f3 100644
--- a/gcc/fortran/invoke.texi
+++ b/gcc/fortran/invoke.texi
@@ -160,7 +160,7 @@ and warnings}.
 @item Debugging Options
 @xref{Debugging Options,,Options for debugging your program or GNU Fortran}.
 @gccoptlist{-fbacktrace -fdump-fortran-optimized -fdump-fortran-original @gol
--fdump-fortran-global -fdump-parse-tree -ffpe-trap=@var{list} @gol
+-fdebug-aux-vars -fdump-fortran-global -fdump-parse-tree -ffpe-trap=@var{list} @gol
 -ffpe-summary=@var{list}
 }
 
@@ -1219,6 +1219,15 @@ change between releases. This option may also generate internal
 compiler errors for features which have only recently been added. This
 option is deprecated; use @code{-fdump-fortran-original} instead.
 
+@item -fdebug-aux-vars
+@opindex @code{fdebug-aux-vars}
+Renames internal variables created by the gfortran front end and makes
+them accessible to a debugger.  The name of the internal variables then
+start with upper-case letters followed by an underscore.  This option is
+useful for debugging the compiler's code generation together with
+@code{-fdump-tree-original} and enabling debugging of the executable
+program by using @code{-g} or @code{-ggdb3}.
+
 @item -fdump-fortran-global
 @opindex @code{fdump-fortran-global}
 Output a list of the global identifiers after translating into
diff --git a/gcc/fortran/lang.opt b/gcc/fortran/lang.opt
index 96ed208cb85..57b0264458e 100644
--- a/gcc/fortran/lang.opt
+++ b/gcc/fortran/lang.opt
@@ -452,6 +452,10 @@ fd-lines-as-comments
 Fortran RejectNegative
 Treat lines with 'D' in column one as comments.
 
+fdebug-aux-vars
+Fortran Var(flag_debug_aux_vars)
+Issue debug information for compiler-generated auxiliary variables.
+
 fdec
 Fortran Var(flag_dec)
 Enable all DEC language extensions.
diff --git a/gcc/fortran/trans.c b/gcc/fortran/trans.c
index 025abe38985..ca0b10ca73d 100644
--- a/gcc/fortran/trans.c
+++ b/gcc/fortran/trans.c
@@ -73,6 +73,45 @@ gfc_advance_chain (tree t, int n)
   return t;
 }
 
+static int num_var;
+
+#define MAX_PREFIX_LEN 20
+
+static tree
+create_var_debug_raw (tree type, const char *prefix)
+{
+  /* Space for prefix + "_" + 10-digit-number + \0.  */
+  char name_buf[MAX_PREFIX_LEN + 1 + 10 + 1];
+  tree t;
+  int i;
+
+  if (prefix == NULL)
+    prefix = "gfc";
+  else
+    gcc_assert (strlen (prefix) <= MAX_PREFIX_LEN);
+
+  for (i = 0; prefix[i] != 0; i++)
+    name_buf[i] = gfc_wide_toupper (prefix[i]);
+
+  snprintf (name_buf + i, sizeof (name_buf) - i, "_%d", num_var++);
+
+  t = build_decl (input_location, VAR_DECL, get_identifier (name_buf), type);
+
+  /* We want debug info for it.  */
+  DECL_IGNORED_P (t) = 0;
+  /* It should not be nameless.  */
+  DECL_NAMELESS (t) = 0;
+
+  /* Make the variable writable.  */
+  TREE_READONLY (t) = 0;
+
+  DECL_EXTERNAL (t) = 0;
+  TREE_STATIC (t) = 0;
+  TREE_USED (t) = 1;
+
+  return t;
+}
+
 /* Creates a variable declaration with a given TYPE.  */
 
 tree
@@ -80,6 +119,9 @@ gfc_create_var_np (tree type, const char *prefix)
 {
   tree t;
 
+  if (flag_debug_aux_vars)
+    return create_var_debug_raw (type, prefix);
+
   t = create_tmp_var_raw (type, prefix);
 
   /* No warnings for anonymous variables.  */
-- 
2.30.2