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On Fri, Jul 30, 2010 at 11:46 AM, H.J. Lu <hjl.tools@gmail.com> wrote: > On Fri, Jul 30, 2010 at 10:54 AM, Xinliang David Li <davidxl@google.com> wrote: >> Why is start offset not 1 to begin with? Let's assume it is correct, >> there are a couple of problems in this patch: >> >> 1) when the precision of the HOST_WIDE_INT is the same as the bitsize >> of the address_mode, max_offset = (HOST_WIDE_INT) 1 << width will >> produce a negative number >> 2) last_off should be initialized to 0 to match the original behavior >> 3) The i&& guard will make sure the loop terminates, but the offset >> compuation will be wrong -- i<<1 will first overflows to a negative >> number, then gets truncated to zero, ?that means when this happens, >> the last_off will be negative when the loop terminates. >> >> David > > I don't know exactly what get_address_cost is supposed to do. Here is > a new patch which avoids overflow and speeds up finding max/min offsets. > The code is wrong for -m32 on 64bit host. We should start with the maximum and minimum offsets like: width = GET_MODE_BITSIZE (address_mode) - 1; if (width > (HOST_BITS_PER_WIDE_INT - 1)) width = HOST_BITS_PER_WIDE_INT - 1; addr = gen_rtx_fmt_ee (PLUS, address_mode, reg1, NULL_RTX); for (i = width; i; i--) { off = -((HOST_WIDE_INT) 1 << i); XEXP (addr, 1) = gen_int_mode (off, address_mode); if (memory_address_addr_space_p (mem_mode, addr, as)) break; } data->min_offset = off; for (i = width; i; i--) { off = ((HOST_WIDE_INT) 1 << i) - 1; XEXP (addr, 1) = gen_int_mode (off, address_mode); if (memory_address_addr_space_p (mem_mode, addr, as)) break; } data->max_offset = off; Here is the updated patch. H.J. --- > H.J. > --- >> >> On Fri, Jul 30, 2010 at 10:27 AM, H.J. Lu <hjl.tools@gmail.com> wrote: >>> On Fri, Jul 30, 2010 at 9:58 AM, Xinliang David Li <davidxl@google.com> wrote: >>>> There is a problem in this patch -- when i wraps to zero and terminate >>>> the loop, the maxoffset computed will be zero which is wrong. >>>> >>>> My previous patch won't have this problem. >>> >>> Your patch changed the start offset. ?Here is the updated patch. >>> >>> >>> H.J. >>>> >>>> David >>>> >>>> On Fri, Jul 30, 2010 at 9:49 AM, Xinliang David Li <davidxl@google.com> wrote: >>>>> This looks fine to me -- Zdenek or other reviewers --- is this one ok? >>>>> >>>>> Thanks, >>>>> >>>>> David >>>>> >>>>> On Fri, Jul 30, 2010 at 8:45 AM, H.J. Lu <hjl.tools@gmail.com> wrote: >>>>>> On Thu, Jul 29, 2010 at 6:04 PM, H.J. Lu <hjl.tools@gmail.com> wrote: >>>>>>> It looks strange: >>>>>>> >>>>>>> + ? ? ?width = (GET_MODE_BITSIZE (address_mode) < ?HOST_BITS_PER_WIDE_INT - 1) >>>>>>> + ? ? ? ? ?? GET_MODE_BITSIZE (address_mode) : HOST_BITS_PER_WIDE_INT - 1; >>>>>>> ? ? ? addr = gen_rtx_fmt_ee (PLUS, address_mode, reg1, NULL_RTX); >>>>>>> - ? ? ?for (i = start; i <= 1 << 20; i <<= 1) >>>>>>> + ? ? ?for (i = 1; i < width; i++) >>>>>>> ? ? ? ?{ >>>>>>> - ? ? ? ? XEXP (addr, 1) = gen_int_mode (i, address_mode); >>>>>>> + ? ? ? ? ?HOST_WIDE_INT offset = (1ll << i); >>>>>>> + ? ? ? ? XEXP (addr, 1) = gen_int_mode (offset, address_mode); >>>>>>> ? ? ? ? ?if (!memory_address_addr_space_p (mem_mode, addr, as)) >>>>>>> ? ? ? ? ? ?break; >>>>>>> ? ? ? ?} >>>>>>> >>>>>>> HOST_WIDE_INT may be long or long long. "1ll" isn't always correct. >>>>>>> I think width can be >= 31. Depending on HOST_WIDE_INT, >>>>>>> >>>>>>> HOST_WIDE_INT offset = -(1ll << i); >>>>>>> >>>>>>> may have different values. The whole function looks odd to me. >>>>>>> >>>>>>> >>>>>> >>>>>> Here is a different approach to check address overflow. >>>>>> >>>>>> >>>>>> -- >>>>>> H.J. >>>>>> -- >>>>>> 2010-07-29 ?H.J. Lu ?<hongjiu.lu@intel.com> >>>>>> >>>>>> ? ? ? ?PR bootstrap/45119 >>>>>> ? ? ? ?* tree-ssa-loop-ivopts.c (get_address_cost): Re-apply revision >>>>>> ? ? ? ?162652. ?Check address overflow. >>>>>> >>>>> >>>> >>> >>> >>> >>> -- >>> H.J. >>> >> > > > > -- > H.J. > -- H.J.
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