On Fri, May 2, 2014 at 5:20 PM, Richard Sandiford
rsand...@linux.vnet.ibm.com wrote:
I locally tried adding an assertion to the wide-int version of set_bit
to make sure that the bit number was in range. It triggers for this
code in boehm.c:mark_reference_fields (quoting trunk version):
/* First word in object corresponds to most significant byte of
bitmap.
In the case of a multiple-word record, we set pointer
bits for all words in the record. This is conservative, but the
size_words != 1 case is impossible in regular java code. */
for (i = 0; i size_words; ++i)
*mask = (*mask).set_bit (ubit - count - i - 1);
if (count = ubit - 2)
*pointer_after_end = 1;
if count + i + 1 = ubit.
AIUI the lower 2 bits are used for something else:
/* Bottom two bits for bitmap mark type are 01. */
mask = mask.set_bit (0);
value = double_int_to_tree (value_type, mask);
which is why the pointer_after_end condition checks for count = ubit - 2.
We never actually use the mask if pointer_after_end is true, so this
patch puts the set_bit in an else branch.
On face value it looks like the condition should be:
count + size_words ubit - 2
instead, but it'd go without saying that I don't really understand this code.
Tested on x86_64-linux-gnu and powerpc64-linux-gnu for wide-int.
OK to install?
Ok.
Thanks,
Richard.
Thanks,
Richard
gcc/java/
* boehm.c (mark_reference_fields): Don't update the mask when
setting pointer_after_end.
Index: gcc/java/boehm.c
===
--- gcc/java/boehm.c2014-01-13 15:05:22.543887284 +
+++ gcc/java/boehm.c2014-05-02 16:08:25.500760537 +0100
@@ -101,17 +101,17 @@ mark_reference_fields (tree field,
*last_set_index = count;
- /* First word in object corresponds to most significant byte of
-bitmap.
-
-In the case of a multiple-word record, we set pointer
-bits for all words in the record. This is conservative, but the
-size_words != 1 case is impossible in regular java code. */
- for (i = 0; i size_words; ++i)
- *mask = wi::set_bit (*mask, ubit - count - i - 1);
-
if (count = ubit - 2)
*pointer_after_end = 1;
+ else
+ /* First word in object corresponds to most significant byte of
+ bitmap.
+
+ In the case of a multiple-word record, we set pointer
+ bits for all words in the record. This is conservative, but the
+ size_words != 1 case is impossible in regular java code. */
+ for (i = 0; i size_words; ++i)
+ *mask = wi::set_bit (*mask, ubit - count - i - 1);
/* If we saw a non-reference field earlier, then we can't
use the count representation. We keep track of that in
