re PR fortran/85599 (warn about short-circuiting of logical expressions for non-pure functions)

2018-07-18  Janus Weil  <janus@gcc.gnu.org>
	    Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/85599
	* dump-parse-tree.c (show_attr): Add handling of implicit_pure.
	* frontend-passes.c (do_warn_function_elimination): Do not warn for
	pure functions.
	* gfortran.h: Add prototypes for gfc_pure_function and
	gfc_implicit_pure_function.
	* gfortran.texi: Add chapter on evaluation of logical expressions.
	* invoke.texi: Mention that -Wfunction-elimination is implied
	by -Wextra.
	* lang.opt: Make -Wextra imply -Wfunction-elimination.
	* resolve.c (pure_function): Rename to gfc_pure_function.
	(gfc_implicit_pure_function): New function.
	(check_pure_function): Use it here.
	(impure_function_callback): New function.
	(resolve_operator): Call it via gfc_expr_walker.


2018-07-18  Janus Weil  <janus@gcc.gnu.org>

	PR fortran/85599
	* gfortran.dg/function_optimize_5.f90: Add option
	'-faggressive-function-elimination' and update dg-warning clauses.
	* gfortran.dg/short_circuiting.f90: New test.

Co-Authored-By: Thomas Koenig <tkoenig@gcc.gnu.org>

From-SVN: r262860

1 files changed, 64 insertions, 5 deletions

diff --git a/gcc/fortran/resolve.c b/gcc/fortran/resolve.c
index 9f88c26..40fa02d 100644
--- a/gcc/fortran/resolve.c
+++ b/gcc/fortran/resolve.c
@@ -2941,8 +2941,8 @@ is_external_proc (gfc_symbol *sym)
 static int
 pure_stmt_function (gfc_expr *, gfc_symbol *);
 
-static int
-pure_function (gfc_expr *e, const char **name)
+int
+gfc_pure_function (gfc_expr *e, const char **name)
 {
   int pure;
   gfc_component *comp;
@@ -2982,6 +2982,21 @@ pure_function (gfc_expr *e, const char **name)
 }
 
 
+/* Check if the expression is a reference to an implicitly pure function.  */
+
+int
+gfc_implicit_pure_function (gfc_expr *e)
+{
+  gfc_component *comp = gfc_get_proc_ptr_comp (e);
+  if (comp)
+    return gfc_implicit_pure (comp->ts.interface);
+  else if (e->value.function.esym)
+    return gfc_implicit_pure (e->value.function.esym);
+  else
+    return 0;
+}
+
+
 static bool
 impure_stmt_fcn (gfc_expr *e, gfc_symbol *sym,
 		 int *f ATTRIBUTE_UNUSED)
@@ -2996,7 +3011,7 @@ impure_stmt_fcn (gfc_expr *e, gfc_symbol *sym,
 	|| e->symtree->n.sym->attr.proc == PROC_ST_FUNCTION)
     return false;
 
-  return pure_function (e, &name) ? false : true;
+  return gfc_pure_function (e, &name) ? false : true;
 }
 
 
@@ -3012,7 +3027,7 @@ pure_stmt_function (gfc_expr *e, gfc_symbol *sym)
 static bool check_pure_function (gfc_expr *e)
 {
   const char *name = NULL;
-  if (!pure_function (e, &name) && name)
+  if (!gfc_pure_function (e, &name) && name)
     {
       if (forall_flag)
 	{
@@ -3034,7 +3049,8 @@ static bool check_pure_function (gfc_expr *e)
 		     "within a PURE procedure", name, &e->where);
 	  return false;
 	}
-      gfc_unset_implicit_pure (NULL);
+      if (!gfc_implicit_pure_function (e))
+	gfc_unset_implicit_pure (NULL);
     }
   return true;
 }
@@ -3822,6 +3838,41 @@ lookup_uop_fuzzy (const char *op, gfc_symtree *uop)
 }
 
 
+/* Callback finding an impure function as an operand to an .and. or
+   .or.  expression.  Remember the last function warned about to
+   avoid double warnings when recursing.  */
+
+static int
+impure_function_callback (gfc_expr **e, int *walk_subtrees ATTRIBUTE_UNUSED,
+			  void *data)
+{
+  gfc_expr *f = *e;
+  const char *name;
+  static gfc_expr *last = NULL;
+  bool *found = (bool *) data;
+
+  if (f->expr_type == EXPR_FUNCTION)
+    {
+      *found = 1;
+      if (f != last && !gfc_pure_function (f, &name)
+	  && !gfc_implicit_pure_function (f))
+	{
+	  if (name)
+	    gfc_warning (OPT_Wfunction_elimination,
+			 "Impure function %qs at %L might not be evaluated",
+			 name, &f->where);
+	  else
+	    gfc_warning (OPT_Wfunction_elimination,
+			 "Impure function at %L might not be evaluated",
+			 &f->where);
+	}
+      last = f;
+    }
+
+  return 0;
+}
+
+
 /* Resolve an operator expression node.  This can involve replacing the
    operation with a user defined function call.  */
 
@@ -3930,6 +3981,14 @@ resolve_operator (gfc_expr *e)
 	    gfc_convert_type (op1, &e->ts, 2);
 	  else if (op2->ts.kind < e->ts.kind)
 	    gfc_convert_type (op2, &e->ts, 2);
+
+	  if (e->value.op.op == INTRINSIC_AND || e->value.op.op == INTRINSIC_OR)
+	    {
+	      /* Warn about short-circuiting
+	         with impure function as second operand.  */
+	      bool op2_f = false;
+	      gfc_expr_walker (&op2, impure_function_callback, &op2_f);
+	    }
 	  break;
 	}