Adjust volatile handling of the operand scanner

The GIMPLE SSA operand scanner handles COMPONENT_REFs that are
not marked TREE_THIS_VOLATILE but have a TREE_THIS_VOLATILE
FIELD_DECL as volatile.  That's inconsistent in how TREE_THIS_VOLATILE
testing on GENERIC refs works which requires operand zero of
component references to mirror TREE_THIS_VOLATILE to the ref
so that testing TREE_THIS_VOLATILE on the outermost reference
is enough to determine the volatileness.

The following patch thus removes FIELD_DECL scanning from
the GIMPLE SSA operand scanner, possibly leaving fewer stmts
marked as gimple_has_volatile_ops.

It shows we miss at least one case in the fortran frontend, though
there's a suspicious amount of COMPONENT_REF creation compared
to little setting of TREE_THIS_VOLATILE.  This fixes the FAIL
of gfortran.dg/volatile11.f90 that would otherwise occur.

Visually inspecting fortran/ reveals a bunch of likely to fix
cases but I don't know the constraints of 'volatile' uses in
the fortran language to assess whether some of these are not
necessary.

2021-08-09  Richard Biener  <rguenther@suse.de>

gcc/
	* tree-ssa-operands.c (operands_scanner::get_expr_operands):
	Do not look at COMPONENT_REF FIELD_DECLs TREE_THIS_VOLATILE
	to determine has_volatile_ops.

gcc/fortran/
	* trans-common.c (create_common): Set TREE_THIS_VOLATILE on the
	COMPONENT_REF if the field is volatile.

2 files changed, 6 insertions, 10 deletions

diff --git a/gcc/fortran/trans-common.c b/gcc/fortran/trans-common.c
index a11cf4c..7bcf18d 100644
--- a/gcc/fortran/trans-common.c
+++ b/gcc/fortran/trans-common.c
@@ -759,10 +759,11 @@ create_common (gfc_common_head *com, segment_info *head, bool saw_equiv)
       else
 	gfc_add_decl_to_function (var_decl);
 
-      SET_DECL_VALUE_EXPR (var_decl,
-			   fold_build3_loc (input_location, COMPONENT_REF,
-					    TREE_TYPE (s->field),
-					    decl, s->field, NULL_TREE));
+      tree comp = build3_loc (input_location, COMPONENT_REF,
+			      TREE_TYPE (s->field), decl, s->field, NULL_TREE);
+      if (TREE_THIS_VOLATILE (s->field))
+	TREE_THIS_VOLATILE (comp) = 1;
+      SET_DECL_VALUE_EXPR (var_decl, comp);
       DECL_HAS_VALUE_EXPR_P (var_decl) = 1;
       GFC_DECL_COMMON_OR_EQUIV (var_decl) = 1;
 
diff --git a/gcc/tree-ssa-operands.c b/gcc/tree-ssa-operands.c
index c155754..ebf7eea 100644
--- a/gcc/tree-ssa-operands.c
+++ b/gcc/tree-ssa-operands.c
@@ -834,12 +834,7 @@ operands_scanner::get_expr_operands (tree *expr_p, int flags)
 	get_expr_operands (&TREE_OPERAND (expr, 0), flags);
 
 	if (code == COMPONENT_REF)
-	  {
-	    if (!(flags & opf_no_vops)
-		&& TREE_THIS_VOLATILE (TREE_OPERAND (expr, 1)))
-	      gimple_set_has_volatile_ops (stmt, true);
-	    get_expr_operands (&TREE_OPERAND (expr, 2), uflags);
-	  }
+	  get_expr_operands (&TREE_OPERAND (expr, 2), uflags);
 	else if (code == ARRAY_REF || code == ARRAY_RANGE_REF)
 	  {
 	    get_expr_operands (&TREE_OPERAND (expr, 1), uflags);