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.c 2014-01-13 15:05:22.543887284 +0000 > +++ gcc/java/boehm.c 2014-05-02 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 >
