On Wed, May 13, 2015 at 03:06:00PM +0000, Joseph Myers wrote:
> > It won't handle e.g. 0 * (unsigned) (1 / 0).
>
> I think this illustrates why handling this in the folding-for-optimization
> is a mistake.
>
> For optimization, it's perfectly fine to fold away 0 * (something without
> side effects), and division by 0 should only be considered to have side
> effects if language semantic options were specified to that effect (such
> as using ubsan), which should then have the effect of producing GENERIC
> that's not a simple division but represents whatever checks are required.
>
> Rather, how about having an extra argument to c_fully_fold_internal (e.g.
> for_int_const) indicating that the folding is of an expression with
> integer constant operands (so this argument would be true in the new case
> of folding the contents of a C_MAYBE_CONST_EXPR with
> C_MAYBE_CONST_EXPR_INT_OPERANDS set)? In that special case,
> c_fully_fold_internal would only fold the expression itself if all
> evaluated operands folded to INTEGER_CSTs (so if something that doesn't
> get folded, such as division by 0, is encountered, then all evaluated
> expressions containing it also don't get folded).
Did you mean something like the following? It is on top of the previous
c_fully_fold_internal patch; if it makes any sense, I'll squash these
into one.
With the following, I don't see any regressions in the C dg.exp testsuite.
This still doesn't reject enum { A = 0 * (unsigned) (1 / 0) };, but note
that we don't reject such an enum at present.
Thanks.
diff --git gcc/c-family/c-common.c gcc/c-family/c-common.c
index 24200f0..1dc181d 100644
--- gcc/c-family/c-common.c
+++ gcc/c-family/c-common.c
@@ -315,7 +315,7 @@ const struct fname_var_t fname_vars[] =
/* Global visibility options. */
struct visibility_flags visibility_options;
-static tree c_fully_fold_internal (tree expr, bool, bool *, bool *);
+static tree c_fully_fold_internal (tree expr, bool, bool *, bool *, bool);
static tree check_case_value (location_t, tree);
static bool check_case_bounds (location_t, tree, tree, tree *, tree *);
@@ -1148,7 +1148,7 @@ c_fully_fold (tree expr, bool in_init, bool *maybe_const)
expr = TREE_OPERAND (expr, 0);
}
ret = c_fully_fold_internal (expr, in_init, maybe_const,
- &maybe_const_itself);
+ &maybe_const_itself, false);
if (eptype)
ret = fold_convert_loc (loc, eptype, ret);
*maybe_const &= maybe_const_itself;
@@ -1161,11 +1161,13 @@ c_fully_fold (tree expr, bool in_init, bool
*maybe_const)
arithmetic overflow (for C90, *MAYBE_CONST_OPERANDS is carried from
both evaluated and unevaluated subexpressions while
*MAYBE_CONST_ITSELF is carried from only evaluated
- subexpressions). */
+ subexpressions). FOR_INT_CONST indicates if EXPR is an expression
+ with integer constant operands, and if any of the operands doesn't
+ get folded to an integer constant, don't fold the expression itself. */
static tree
c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands,
- bool *maybe_const_itself)
+ bool *maybe_const_itself, bool for_int_const)
{
tree ret = expr;
enum tree_code code = TREE_CODE (expr);
@@ -1212,7 +1214,7 @@ c_fully_fold_internal (tree expr, bool in_init, bool
*maybe_const_operands,
{
*maybe_const_itself = false;
inner = c_fully_fold_internal (inner, in_init, maybe_const_operands,
- maybe_const_itself);
+ maybe_const_itself, true);
}
if (pre && !in_init)
ret = build2 (COMPOUND_EXPR, TREE_TYPE (expr), pre, inner);
@@ -1263,7 +1265,7 @@ c_fully_fold_internal (tree expr, bool in_init, bool
*maybe_const_operands,
op1 = TREE_OPERAND (expr, 1);
op2 = TREE_OPERAND (expr, 2);
op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
- maybe_const_itself);
+ maybe_const_itself, for_int_const);
STRIP_TYPE_NOPS (op0);
if (op0 != orig_op0)
ret = build3 (COMPONENT_REF, TREE_TYPE (expr), op0, op1, op2);
@@ -1280,10 +1282,10 @@ c_fully_fold_internal (tree expr, bool in_init, bool
*maybe_const_operands,
op2 = TREE_OPERAND (expr, 2);
op3 = TREE_OPERAND (expr, 3);
op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
- maybe_const_itself);
+ maybe_const_itself, for_int_const);
STRIP_TYPE_NOPS (op0);
op1 = c_fully_fold_internal (op1, in_init, maybe_const_operands,
- maybe_const_itself);
+ maybe_const_itself, for_int_const);
STRIP_TYPE_NOPS (op1);
op1 = decl_constant_value_for_optimization (op1);
if (op0 != orig_op0 || op1 != orig_op1)
@@ -1340,7 +1342,7 @@ c_fully_fold_internal (tree expr, bool in_init, bool
*maybe_const_operands,
orig_op0 = op0 = TREE_OPERAND (expr, 0);
orig_op1 = op1 = TREE_OPERAND (expr, 1);
op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
- maybe_const_itself);
+ maybe_const_itself, for_int_const);
STRIP_TYPE_NOPS (op0);
if (code != MODIFY_EXPR
&& code != PREDECREMENT_EXPR
@@ -1352,9 +1354,14 @@ c_fully_fold_internal (tree expr, bool in_init, bool
*maybe_const_operands,
expression for the sake of conversion warnings. */
if (code != MODIFY_EXPR)
op1 = c_fully_fold_internal (op1, in_init, maybe_const_operands,
- maybe_const_itself);
+ maybe_const_itself, for_int_const);
STRIP_TYPE_NOPS (op1);
op1 = decl_constant_value_for_optimization (op1);
+
+ if (for_int_const && (TREE_CODE (op0) != INTEGER_CST
+ || TREE_CODE (op1) != INTEGER_CST))
+ goto out;
+
if (op0 != orig_op0 || op1 != orig_op1 || in_init)
ret = in_init
? fold_build2_initializer_loc (loc, code, TREE_TYPE (expr), op0, op1)
@@ -1424,7 +1431,7 @@ c_fully_fold_internal (tree expr, bool in_init, bool
*maybe_const_operands,
/* Unary operations. */
orig_op0 = op0 = TREE_OPERAND (expr, 0);
op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
- maybe_const_itself);
+ maybe_const_itself, for_int_const);
STRIP_TYPE_NOPS (op0);
if (code != ADDR_EXPR && code != REALPART_EXPR && code != IMAGPART_EXPR)
op0 = decl_constant_value_for_optimization (op0);
@@ -1472,14 +1479,16 @@ c_fully_fold_internal (tree expr, bool in_init, bool
*maybe_const_operands,
arguments. */
orig_op0 = op0 = TREE_OPERAND (expr, 0);
orig_op1 = op1 = TREE_OPERAND (expr, 1);
- op0 = c_fully_fold_internal (op0, in_init, &op0_const, &op0_const_self);
+ op0 = c_fully_fold_internal (op0, in_init, &op0_const, &op0_const_self,
+ for_int_const);
STRIP_TYPE_NOPS (op0);
unused_p = (op0 == (code == TRUTH_ANDIF_EXPR
? truthvalue_false_node
: truthvalue_true_node));
c_disable_warnings (unused_p);
- op1 = c_fully_fold_internal (op1, in_init, &op1_const, &op1_const_self);
+ op1 = c_fully_fold_internal (op1, in_init, &op1_const, &op1_const_self,
+ for_int_const);
STRIP_TYPE_NOPS (op1);
c_enable_warnings (unused_p);
@@ -1510,16 +1519,19 @@ c_fully_fold_internal (tree expr, bool in_init, bool
*maybe_const_operands,
orig_op0 = op0 = TREE_OPERAND (expr, 0);
orig_op1 = op1 = TREE_OPERAND (expr, 1);
orig_op2 = op2 = TREE_OPERAND (expr, 2);
- op0 = c_fully_fold_internal (op0, in_init, &op0_const, &op0_const_self);
+ op0 = c_fully_fold_internal (op0, in_init, &op0_const, &op0_const_self,
+ for_int_const);
STRIP_TYPE_NOPS (op0);
c_disable_warnings (op0 == truthvalue_false_node);
- op1 = c_fully_fold_internal (op1, in_init, &op1_const, &op1_const_self);
+ op1 = c_fully_fold_internal (op1, in_init, &op1_const, &op1_const_self,
+ for_int_const);
STRIP_TYPE_NOPS (op1);
c_enable_warnings (op0 == truthvalue_false_node);
c_disable_warnings (op0 == truthvalue_true_node);
- op2 = c_fully_fold_internal (op2, in_init, &op2_const, &op2_const_self);
+ op2 = c_fully_fold_internal (op2, in_init, &op2_const, &op2_const_self,
+ for_int_const);
STRIP_TYPE_NOPS (op2);
c_enable_warnings (op0 == truthvalue_true_node);
Marek
