On Tue, Jan 16, 2018 at 08:57:38AM +0100, Richard Biener wrote:
> > - unsigned HOST_WIDE_INT off
> > - = (tree_to_uhwi (DECL_FIELD_OFFSET (field))
> > - + tree_to_uhwi (DECL_FIELD_BIT_OFFSET (field)) / BITS_PER_UNIT);
> > - if ((off % warn_if_not_align) != 0)
> > - warning (opt_w, "%q+D offset %wu in %qT isn't aligned to %u",
> > + tree off = byte_position (field);
> > + if (!multiple_of_p (TREE_TYPE (off), off, size_int (warn_if_not_align)))
>
> multiple_of_p also returns 0 if it doesn't know (for the non-constant
> case obviously), so the warning should say "may be not aligned"? Or
> we don't want any false positives which means multiple_of_p should get
> a worker factored out that returns a tri-state value?
tri-state sounds optimizing for the very uncommon case, I think it must be
very rare in practice when we could prove it must be not aligned and
especially we'd need to extend it a lot to handle those cases.
Here is an updated patch which says may not be aligned if off is
non-constant. When extending the testcase, I've noticed we don't handle
IMHO quite important case in multiple_of_p, so the patch handles that too.
I've tried not to increase asymptotic complexity of multiple_of_p, so except
for the cases where both arguments are INTEGER_CSTs it shouldn't call
multiple_of_p more times than before.
Ok for trunk if this passes bootstrap/regtest?
2018-01-16 Jakub Jelinek <ja...@redhat.com>
PR c/83844
* stor-layout.c (handle_warn_if_not_align): Use byte_position and
multiple_of_p instead of unchecked tree_to_uhwi and UHWI check.
If off is not INTEGER_CST, issue a may not be aligned warning
rather than isn't aligned. Use isn%'t rather than isn't.
* fold-const.c (multiple_of_p) <case BIT_AND_EXPR>: Don't fall through
into MULT_EXPR.
<case MULT_EXPR>: Improve the case when bottom and one of the
MULT_EXPR operands are INTEGER_CSTs and bottom is multiple of that
operand, in that case check if the other operand is multiple of
bottom divided by the INTEGER_CST operand.
* gcc.dg/pr83844.c: New test.
--- gcc/stor-layout.c.jj 2018-01-15 22:40:14.009263280 +0100
+++ gcc/stor-layout.c 2018-01-16 10:01:48.135111031 +0100
@@ -1150,12 +1150,16 @@ handle_warn_if_not_align (tree field, un
warning (opt_w, "alignment %u of %qT is less than %u",
record_align, context, warn_if_not_align);
- unsigned HOST_WIDE_INT off
- = (tree_to_uhwi (DECL_FIELD_OFFSET (field))
- + tree_to_uhwi (DECL_FIELD_BIT_OFFSET (field)) / BITS_PER_UNIT);
- if ((off % warn_if_not_align) != 0)
- warning (opt_w, "%q+D offset %wu in %qT isn't aligned to %u",
- field, off, context, warn_if_not_align);
+ tree off = byte_position (field);
+ if (!multiple_of_p (TREE_TYPE (off), off, size_int (warn_if_not_align)))
+ {
+ if (TREE_CODE (off) == INTEGER_CST)
+ warning (opt_w, "%q+D offset %E in %qT isn%'t aligned to %u",
+ field, off, context, warn_if_not_align);
+ else
+ warning (opt_w, "%q+D offset %E in %qT may not be aligned to %u",
+ field, off, context, warn_if_not_align);
+ }
}
/* Called from place_field to handle unions. */
--- gcc/fold-const.c.jj 2018-01-15 10:02:04.119181355 +0100
+++ gcc/fold-const.c 2018-01-16 10:48:10.444360796 +0100
@@ -12595,9 +12595,34 @@ multiple_of_p (tree type, const_tree top
a multiple of BOTTOM then TOP is a multiple of BOTTOM. */
if (!integer_pow2p (bottom))
return 0;
- /* FALLTHRU */
+ return (multiple_of_p (type, TREE_OPERAND (top, 1), bottom)
+ || multiple_of_p (type, TREE_OPERAND (top, 0), bottom));
case MULT_EXPR:
+ if (TREE_CODE (bottom) == INTEGER_CST)
+ {
+ op1 = TREE_OPERAND (top, 0);
+ op2 = TREE_OPERAND (top, 1);
+ if (TREE_CODE (op1) == INTEGER_CST)
+ std::swap (op1, op2);
+ if (TREE_CODE (op2) == INTEGER_CST)
+ {
+ if (multiple_of_p (type, op2, bottom))
+ return 1;
+ /* Handle multiple_of_p ((x * 2 + 2) * 4, 8). */
+ if (multiple_of_p (type, bottom, op2))
+ {
+ widest_int w = wi::sdiv_trunc (wi::to_widest (bottom),
+ wi::to_widest (op2));
+ if (wi::fits_to_tree_p (w, TREE_TYPE (bottom)))
+ {
+ op2 = wide_int_to_tree (TREE_TYPE (bottom), w);
+ return multiple_of_p (type, op1, op2);
+ }
+ }
+ return multiple_of_p (type, op1, bottom);
+ }
+ }
return (multiple_of_p (type, TREE_OPERAND (top, 1), bottom)
|| multiple_of_p (type, TREE_OPERAND (top, 0), bottom));
--- gcc/testsuite/gcc.dg/pr83844.c.jj 2018-01-16 09:56:57.459175232 +0100
+++ gcc/testsuite/gcc.dg/pr83844.c 2018-01-16 10:02:55.494096157 +0100
@@ -0,0 +1,36 @@
+/* PR c/83844 */
+/* { dg-do compile } */
+/* { dg-options "-O0 -Wall" } */
+
+typedef unsigned long long __u64
__attribute__((aligned(4),warn_if_not_aligned(8)));
+void bar (void *, void *, void *);
+
+void
+foo (int n)
+{
+ struct A
+ {
+ int i1;
+ int i2;
+ int i3[n];
+ __u64 x; /* { dg-warning "in 'struct A' may not be aligned to 8" } */
+ } __attribute__((aligned (8)));
+ struct B
+ {
+ int i1;
+ int i2;
+ long long i3[n];
+ __u64 x;
+ } __attribute__((aligned (8)));
+ struct C
+ {
+ int i1;
+ int i2;
+ int i3[2 * n];
+ __u64 x;
+ } __attribute__((aligned (8)));
+ struct A a;
+ struct B b;
+ struct C c;
+ bar (&a, &b, &c);
+}
Jakub
