On Mon, 16 Jan 2012, Richard Guenther wrote:
> 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).
Which works besides now FAILing gcc.dg/strncpy-fix-1.c. We get
a "value computed is not used" warning because we are still folding
the strncpy to a memcpy because we fold all builtin calls at the very
point they are created (build_function_call_vec):
if (name != NULL_TREE
&& !strncmp (IDENTIFIER_POINTER (name), "__builtin_", 10))
{
if (require_constant_value)
result =
fold_build_call_array_initializer_loc (loc, TREE_TYPE (fntype),
function, nargs,
argarray);
else
result = fold_build_call_array_loc (loc, TREE_TYPE (fntype),
function, nargs, argarray);
"Fixed" by not doing that if !require_constant_value. We'll fold
it during the c_fully_fold call anyway (and during gimplification again).
Re-testing as follows.
Richard.
2012-01-13 Richard Guenther <[email protected]>
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.
(build_function_call_vec): Do not fold calls here if we do not
require a constant value.
* 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)
*************** build_function_call_vec (location_t loc,
*** 2826,2841 ****
/* Check that the arguments to the function are valid. */
check_function_arguments (fntype, nargs, argarray);
! if (name != NULL_TREE
&& !strncmp (IDENTIFIER_POINTER (name), "__builtin_", 10))
{
! if (require_constant_value)
! result =
! fold_build_call_array_initializer_loc (loc, TREE_TYPE (fntype),
! function, nargs, argarray);
! else
! result = fold_build_call_array_loc (loc, TREE_TYPE (fntype),
! function, nargs, argarray);
if (TREE_CODE (result) == NOP_EXPR
&& TREE_CODE (TREE_OPERAND (result, 0)) == INTEGER_CST)
STRIP_TYPE_NOPS (result);
--- 2826,2838 ----
/* Check that the arguments to the function are valid. */
check_function_arguments (fntype, nargs, argarray);
! if (require_constant_value
! && name != NULL_TREE
&& !strncmp (IDENTIFIER_POINTER (name), "__builtin_", 10))
{
! result =
! fold_build_call_array_initializer_loc (loc, TREE_TYPE (fntype),
! function, nargs, argarray);
if (TREE_CODE (result) == NOP_EXPR
&& TREE_CODE (TREE_OPERAND (result, 0)) == INTEGER_CST)
STRIP_TYPE_NOPS (result);
*************** c_finish_bc_stmt (location_t loc, tree *
*** 9163,9168 ****
--- 9160,9169 ----
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))
*************** c_process_expr_stmt (location_t loc, tre
*** 9186,9193 ****
if (!expr)
return NULL_TREE;
- expr = c_fully_fold (expr, false, NULL);
-
if (warn_sequence_point)
verify_sequence_points (expr);
--- 9187,9192 ----
*************** c_process_expr_stmt (location_t loc, tre
*** 9213,9218 ****
--- 9212,9219 ----
|| 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))
