On Fri, 13 Jan 2012, Joseph S. Myers wrote:
> On Fri, 13 Jan 2012, Richard Guenther wrote:
>
> > This fixes PR37985 where since
> > http://gcc.gnu.org/ml/gcc-patches/2006-08/msg01041.html we
> > mark conversions produced by convert_to_integer with TREE_NO_WARNING.
> > This may shadow "real" stmts with no effects, thus we should
> > simply strip them again before checking for TREE_SIDE_EFFECTS.
> >
> > Bootstrap & regtest pending on x86_64-unknown-linux-gnu.
> >
> > Ok if that passes?
>
> OK.
It FAILs gcc.dg/20040202-1.c (we warn about a folded memcpy). It
looks like wrapping things in TREE_NO_WARNING NOP_EXPRs is
fragile as soon as you consider multiple warning kinds (thus, of
course the patch causing this regression is at fault).
OTOH for the regression warning on folded stmts I really wonder
why c_process_expr_stmt folds at all before emitting warnings - why
intentionally divert from the source AST here? I'm testing
the following before giving up on this regression (which solves
the gcc.dg/20040202-1.c FAIL at least).
Richard.
2012-01-13 Richard Guenther <rguent...@suse.de>
PR c/37985
* c-typeck.c (emit_side_effect_warnings): Strip conversions
with TREE_NO_WARNING.
(c_process_expr_stmt): Fold the stmt after emitting warnings.
* gcc.dg/Wunused-value-4.c: New testcase.
Index: gcc/testsuite/gcc.dg/Wunused-value-4.c
===================================================================
*** gcc/testsuite/gcc.dg/Wunused-value-4.c (revision 0)
--- gcc/testsuite/gcc.dg/Wunused-value-4.c (revision 0)
***************
*** 0 ****
--- 1,9 ----
+ /* PR c/37985 */
+ /* { dg-do compile } */
+ /* { dg-options "-Wunused-value" } */
+
+ unsigned char foo(unsigned char a)
+ {
+ a >> 2; /* { dg-warning "statement with no effect" } */
+ return a;
+ }
Index: gcc/c-typeck.c
===================================================================
--- gcc/c-typeck.c (revision 183205)
+++ gcc/c-typeck.c (working copy)
@@ -9163,6 +9163,10 @@ c_finish_bc_stmt (location_t loc, tree *
static void
emit_side_effect_warnings (location_t loc, tree expr)
{
+ /* Strip conversions marked with TREE_NO_WARNING. */
+ while (TREE_NO_WARNING (expr) && CONVERT_EXPR_P (expr))
+ expr = TREE_OPERAND (expr, 0);
+
if (expr == error_mark_node)
;
else if (!TREE_SIDE_EFFECTS (expr))
@@ -9186,8 +9190,6 @@ c_process_expr_stmt (location_t loc, tre
if (!expr)
return NULL_TREE;
- expr = c_fully_fold (expr, false, NULL);
-
if (warn_sequence_point)
verify_sequence_points (expr);
@@ -9213,6 +9215,8 @@ c_process_expr_stmt (location_t loc, tre
|| TREE_CODE (exprv) == ADDR_EXPR)
mark_exp_read (exprv);
+ expr = c_fully_fold (expr, false, NULL);
+
/* If the expression is not of a type to which we cannot assign a line
number, wrap the thing in a no-op NOP_EXPR. */
if (DECL_P (expr) || CONSTANT_CLASS_P (expr))
