[Bug c/51455] Possible uninitialized register use when array subscript is unsigned
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51455 --- Comment #1 from Andrew Pinski pinskia at gcc dot gnu.org 2011-12-07 19:10:55 UTC --- ((unsigned char *)offsets)[index] still sign extends to int.
[Bug c/51455] Possible uninitialized register use when array subscript is unsigned
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51455 --- Comment #2 from frederik.deweerdt at gmail dot com 2011-12-07 19:25:30 UTC --- (In reply to comment #1) ((unsigned char *)offsets)[index] still sign extends to int. I'm not sure how to parse this. My problem is that '((unsigned char *)offsets)[index]' uses the 'l' version of mov and eax as destination register. I would expect the generate asm to use the 'q' version of mov and use rax as destination register.
[Bug c/51455] Possible uninitialized register use when array subscript is unsigned
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51455 --- Comment #3 from Andrew Pinski pinskia at gcc dot gnu.org 2011-12-07 19:28:29 UTC --- movzbl 0x20d(%rsp),%eax is the same as: movzbq 0x20d(%rsp),%rax as all l instructions zero extend to q.
[Bug c/51455] Possible uninitialized register use when array subscript is unsigned
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51455 --- Comment #4 from Jakub Jelinek jakub at gcc dot gnu.org 2011-12-07 19:30:21 UTC --- Probably time for you to read the docs. E.g. AMD 24592 pdf, in 3.1.2 says: In general, byte and word operands are stored in the low 8 or 16 bits of GPRs without modifying their high 56 or 48 bits, respectively. Doubleword operands, however, are normally stored in the low 32 bits of GPRs and zero-extended to 64 bits. Of course movzbl insn clears all upper 56 bits of the destination register, like movzbq, but is one byte shorter.
[Bug c/51455] Possible uninitialized register use when array subscript is unsigned
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51455 Jakub Jelinek jakub at gcc dot gnu.org changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED CC||jakub at gcc dot gnu.org Resolution||INVALID --- Comment #5 from Jakub Jelinek jakub at gcc dot gnu.org 2011-12-07 19:31:10 UTC --- Invalid.
