This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH] Don't fold away division by zero (PR middle-end/66127)
- From: Marek Polacek <polacek at redhat dot com>
- To: Joseph Myers <joseph at codesourcery dot com>
- Cc: Jakub Jelinek <jakub at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, Richard Biener <rguenther at suse dot de>
- Date: Thu, 14 May 2015 13:03:16 +0200
- Subject: Re: [PATCH] Don't fold away division by zero (PR middle-end/66127)
- Authentication-results: sourceware.org; auth=none
- References: <20150513134111 dot GA27320 at redhat dot com> <20150513135509 dot GE1751 at tucnak dot redhat dot com> <20150513141115 dot GC27320 at redhat dot com> <alpine dot DEB dot 2 dot 10 dot 1505131456470 dot 30846 at digraph dot polyomino dot org dot uk> <20150513191803 dot GG27320 at redhat dot com> <alpine dot DEB dot 2 dot 10 dot 1505132240340 dot 29221 at digraph dot polyomino dot org dot uk>
On Wed, May 13, 2015 at 10:46:06PM +0000, Joseph Myers wrote:
> Yes. The two patches are OK together, though I think it would be better
Thanks.
> to add for_int_const checks also in the cases of unary operations, &&, ||
> and ?: (the last three being cases where it's only the evaluated operands
> that need to fold to INTEGER_CSTs, not any unevaluated operands). It may
> well be the case that no folding at present can fold any of those cases to
> an INTEGER_CST when it shouldn't be one, but I don't think we should rely
> on that.
Yeah, I couldn't find a case where it would trigger, but I added for_int_const
checks for the other cases all the same.
I'm attaching the patch here for archival purposes.
Bootstrapped/regtested on x86_64-linux, applying to trunk.
2015-05-14 Marek Polacek <polacek@redhat.com>
PR c/66066
PR c/66127
* c-common.c (c_fully_fold): Pass false down to c_fully_fold_internal.
(c_fully_fold_internal): Fold C_MAYBE_CONST_EXPRs with
C_MAYBE_CONST_EXPR_INT_OPERANDS set. Add FOR_INT_CONST argument and
use it. If FOR_INT_CONST, require that all evaluated operands be
INTEGER_CSTs.
* c-typeck.c (digest_init): Call pedwarn_init with OPT_Wpedantic
rather than with 0.
* gcc.dg/pr14649-1.c: Add -Wpedantic.
* gcc.dg/pr19984.c: Likewise.
* gcc.dg/pr66066-1.c: New test.
* gcc.dg/pr66066-2.c: New test.
* gcc.dg/pr66066-3.c: New test.
diff --git gcc/c-family/c-common.c gcc/c-family/c-common.c
index 7e5ac72..31c4c0d 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);
@@ -1209,7 +1211,11 @@ c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands,
if (C_MAYBE_CONST_EXPR_NON_CONST (expr))
*maybe_const_operands = false;
if (C_MAYBE_CONST_EXPR_INT_OPERANDS (expr))
- *maybe_const_itself = false;
+ {
+ *maybe_const_itself = false;
+ inner = c_fully_fold_internal (inner, in_init, maybe_const_operands,
+ maybe_const_itself, true);
+ }
if (pre && !in_init)
ret = build2 (COMPOUND_EXPR, TREE_TYPE (expr), pre, inner);
else
@@ -1259,7 +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);
@@ -1276,10 +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)
@@ -1336,7 +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
@@ -1348,9 +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)
@@ -1420,10 +1431,14 @@ 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);
+
+ if (for_int_const && TREE_CODE (op0) != INTEGER_CST)
+ goto out;
+
/* ??? Cope with user tricks that amount to offsetof. The middle-end is
not prepared to deal with them if they occur in initializers. */
if (op0 != orig_op0
@@ -1468,17 +1483,25 @@ 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);
+ if (for_int_const
+ && (TREE_CODE (op0) != INTEGER_CST
+ /* Require OP1 be an INTEGER_CST only if it's evaluated. */
+ || (!unused_p && 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)
@@ -1506,19 +1529,30 @@ 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);
+ if (for_int_const
+ && (TREE_CODE (op0) != INTEGER_CST
+ /* Only the evaluated operand must be an INTEGER_CST. */
+ || (op0 == truthvalue_true_node
+ ? TREE_CODE (op1) != INTEGER_CST
+ : TREE_CODE (op2) != INTEGER_CST)))
+ goto out;
+
if (op0 != orig_op0 || op1 != orig_op1 || op2 != orig_op2)
ret = fold_build3_loc (loc, code, TREE_TYPE (expr), op0, op1, op2);
else
diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
index 3fcb7c2..9b883a2 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -6864,7 +6864,7 @@ digest_init (location_t init_loc, tree type, tree init, tree origtype,
inside_init = error_mark_node;
}
else if (require_constant && !maybe_const)
- pedwarn_init (init_loc, 0,
+ pedwarn_init (init_loc, OPT_Wpedantic,
"initializer element is not a constant expression");
/* Added to enable additional -Wsuggest-attribute=format warnings. */
diff --git gcc/testsuite/gcc.dg/pr14649-1.c gcc/testsuite/gcc.dg/pr14649-1.c
index 34f42f0..b9fc4b9 100644
--- gcc/testsuite/gcc.dg/pr14649-1.c
+++ gcc/testsuite/gcc.dg/pr14649-1.c
@@ -1,6 +1,6 @@
/* PR c/14649 */
/* { dg-do compile } */
-/* { dg-options "-O2" } */
+/* { dg-options "-O2 -Wpedantic" } */
double atan(double);
diff --git gcc/testsuite/gcc.dg/pr19984.c gcc/testsuite/gcc.dg/pr19984.c
index 5323c46..a628e0e 100644
--- gcc/testsuite/gcc.dg/pr19984.c
+++ gcc/testsuite/gcc.dg/pr19984.c
@@ -1,6 +1,6 @@
/* PR c/19984 */
/* { dg-do compile } */
-/* { dg-options "-O2 -std=c99" } */
+/* { dg-options "-O2 -std=c99 -Wpedantic" } */
double nan (const char *);
diff --git gcc/testsuite/gcc.dg/pr66066-1.c gcc/testsuite/gcc.dg/pr66066-1.c
index e69de29..7a1d342 100644
--- gcc/testsuite/gcc.dg/pr66066-1.c
+++ gcc/testsuite/gcc.dg/pr66066-1.c
@@ -0,0 +1,37 @@
+/* PR c/66066 */
+/* { dg-do compile } */
+/* { dg-options "-Wno-div-by-zero" } */
+
+/* Accept these unless -pedantic-errors/-Werror. */
+int a1 = -1 << 0;
+int a2 = -1 << 0 | 0;
+int a3 = -1 << 0 & 1;
+int a4 = -1 << 2 ^ 1;
+int a5 = 4 & -1 << 2;
+int a6 = (-1 << 2) ^ (1 >> 1);
+int a7 = 0 || (-1 << 1);
+int a8 = 0 ? 2 : (-1 << 1);
+int a9 = 1 && -1 << 0;
+int a10 = !(-1 << 0);
+
+/* Don't accept these. */
+int b1 = 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b2 = 1 / (1 / 0); /* { dg-error "initializer element is not constant" } */
+int b3 = 0 ? 2 : 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b4 = 0 || 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b5 = 0 * (1 / 0); /* { dg-error "initializer element is not constant" } */
+int b6 = 1 * (1 / 0); /* { dg-error "initializer element is not constant" } */
+int b7 = (1 / 0) * 0; /* { dg-error "initializer element is not constant" } */
+int b8 = (1 / 0) * 1; /* { dg-error "initializer element is not constant" } */
+int b9 = 1 && 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b10 = !(1 / 0); /* { dg-error "initializer element is not constant" } */
+int c1 = 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c2 = 1 / (1 % 0); /* { dg-error "initializer element is not constant" } */
+int c3 = 0 ? 2 : 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c4 = 0 || 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c5 = 0 * (1 % 0); /* { dg-error "initializer element is not constant" } */
+int c6 = 1 * (1 % 0); /* { dg-error "initializer element is not constant" } */
+int c7 = (1 % 0) * 0; /* { dg-error "initializer element is not constant" } */
+int c8 = (1 % 0) * 1; /* { dg-error "initializer element is not constant" } */
+int c9 = 1 && 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c10 = !(1 % 0); /* { dg-error "initializer element is not constant" } */
diff --git gcc/testsuite/gcc.dg/pr66066-2.c gcc/testsuite/gcc.dg/pr66066-2.c
index e69de29..848fe85 100644
--- gcc/testsuite/gcc.dg/pr66066-2.c
+++ gcc/testsuite/gcc.dg/pr66066-2.c
@@ -0,0 +1,37 @@
+/* PR c/66066 */
+/* { dg-do compile } */
+/* { dg-options "-Wno-div-by-zero -Wpedantic" } */
+
+/* Accept these unless -pedantic-errors/-Werror. */
+int a1 = -1 << 0; /* { dg-warning "initializer element is not a constant expression" } */
+int a2 = -1 << 0 | 0; /* { dg-warning "initializer element is not a constant expression" } */
+int a3 = -1 << 0 & 1; /* { dg-warning "initializer element is not a constant expression" } */
+int a4 = -1 << 2 ^ 1; /* { dg-warning "initializer element is not a constant expression" } */
+int a5 = 4 & -1 << 2; /* { dg-warning "initializer element is not a constant expression" } */
+int a6 = (-1 << 2) ^ (1 >> 1); /* { dg-warning "initializer element is not a constant expression" } */
+int a7 = 0 || (-1 << 1); /* { dg-warning "initializer element is not a constant expression" } */
+int a8 = 0 ? 2 : (-1 << 1); /* { dg-warning "initializer element is not a constant expression" } */
+int a9 = 1 && -1 << 0; /* { dg-warning "initializer element is not a constant expression" } */
+int a10 = !(-1 << 0); /* { dg-warning "initializer element is not a constant expression" } */
+
+/* Don't accept these. */
+int b1 = 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b2 = 1 / (1 / 0); /* { dg-error "initializer element is not constant" } */
+int b3 = 0 ? 2 : 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b4 = 0 || 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b5 = 0 * (1 / 0); /* { dg-error "initializer element is not constant" } */
+int b6 = 1 * (1 / 0); /* { dg-error "initializer element is not constant" } */
+int b7 = (1 / 0) * 0; /* { dg-error "initializer element is not constant" } */
+int b8 = (1 / 0) * 1; /* { dg-error "initializer element is not constant" } */
+int b9 = 1 && 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b10 = !(1 / 0); /* { dg-error "initializer element is not constant" } */
+int c1 = 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c2 = 1 / (1 % 0); /* { dg-error "initializer element is not constant" } */
+int c3 = 0 ? 2 : 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c4 = 0 || 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c5 = 0 * (1 % 0); /* { dg-error "initializer element is not constant" } */
+int c6 = 1 * (1 % 0); /* { dg-error "initializer element is not constant" } */
+int c7 = (1 % 0) * 0; /* { dg-error "initializer element is not constant" } */
+int c8 = (1 % 0) * 1; /* { dg-error "initializer element is not constant" } */
+int c9 = 1 && 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c10 = !(1 % 0); /* { dg-error "initializer element is not constant" } */
diff --git gcc/testsuite/gcc.dg/pr66066-3.c gcc/testsuite/gcc.dg/pr66066-3.c
index e69de29..99ffec6 100644
--- gcc/testsuite/gcc.dg/pr66066-3.c
+++ gcc/testsuite/gcc.dg/pr66066-3.c
@@ -0,0 +1,37 @@
+/* PR c/66066 */
+/* { dg-do compile } */
+/* { dg-options "-Wno-div-by-zero -pedantic-errors" } */
+
+/* Accept these unless -pedantic-errors/-Werror. */
+int a1 = -1 << 0; /* { dg-error "initializer element is not a constant expression" } */
+int a2 = -1 << 0 | 0; /* { dg-error "initializer element is not a constant expression" } */
+int a3 = -1 << 0 & 1; /* { dg-error "initializer element is not a constant expression" } */
+int a4 = -1 << 2 ^ 1; /* { dg-error "initializer element is not a constant expression" } */
+int a5 = 4 & -1 << 2; /* { dg-error "initializer element is not a constant expression" } */
+int a6 = (-1 << 2) ^ (1 >> 1); /* { dg-error "initializer element is not a constant expression" } */
+int a7 = 0 || (-1 << 1); /* { dg-error "initializer element is not a constant expression" } */
+int a8 = 0 ? 2 : (-1 << 1); /* { dg-error "initializer element is not a constant expression" } */
+int a9 = 1 && -1 << 0; /* { dg-error "initializer element is not a constant expression" } */
+int a10 = !(-1 << 0); /* { dg-error "initializer element is not a constant expression" } */
+
+/* Don't accept these. */
+int b1 = 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b2 = 1 / (1 / 0); /* { dg-error "initializer element is not constant" } */
+int b3 = 0 ? 2 : 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b4 = 0 || 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b5 = 0 * (1 / 0); /* { dg-error "initializer element is not constant" } */
+int b6 = 1 * (1 / 0); /* { dg-error "initializer element is not constant" } */
+int b7 = (1 / 0) * 0; /* { dg-error "initializer element is not constant" } */
+int b8 = (1 / 0) * 1; /* { dg-error "initializer element is not constant" } */
+int b9 = 1 && 1 / 0; /* { dg-error "initializer element is not constant" } */
+int b10 = !(1 / 0); /* { dg-error "initializer element is not constant" } */
+int c1 = 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c2 = 1 / (1 % 0); /* { dg-error "initializer element is not constant" } */
+int c3 = 0 ? 2 : 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c4 = 0 || 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c5 = 0 * (1 % 0); /* { dg-error "initializer element is not constant" } */
+int c6 = 1 * (1 % 0); /* { dg-error "initializer element is not constant" } */
+int c7 = (1 % 0) * 0; /* { dg-error "initializer element is not constant" } */
+int c8 = (1 % 0) * 1; /* { dg-error "initializer element is not constant" } */
+int c9 = 1 && 1 % 0; /* { dg-error "initializer element is not constant" } */
+int c10 = !(1 % 0); /* { dg-error "initializer element is not constant" } */
Marek