| Message ID | 87ip92x17v.fsf@talisman.default |
|---|---|
| State | New |
| Headers | show |
On Sun, 18 Nov 2012, Richard Sandiford wrote: > HOST_WIDE_INT start = bitpos_ - (bitpos_ % unit); > if (bitregion_start_ && start < bitregion_start_) > break; > - if (bitregion_end_ && start + unit > bitregion_end_ + 1) > + if (start + unit > bitregion_end_ + 1) This causes: /home/dave/gnu/gcc/objdir/./prev-gcc/g++ -B/home/dave/gnu/gcc/objdir/./prev-gcc/ -B/home/dave/opt/gnu/gcc/gcc-4.8.0/hppa-linux-gnu/bin/ -nostdinc++ -B/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/src/.libs -B/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/libsupc++/.libs -I/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/include/hppa-linux-gnu -I/home/dave/gnu/gcc /objdir/prev-hppa-linux-gnu/libstdc++-v3/include -I/home/dave/gnu/gcc/gcc/libstdc++-v3/libsupc++ -L/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/sr c/.libs -L/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/libsupc++/.libs -c -g -O2 -DIN_GCC -fno-exceptions -fno-rtti -fasynchronous-unwind-tabl es -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wmissing-format-attribut e -pedantic -Wno-long-long -Wno-variadic-macros -Wno-overlength-strings -Werror -fno-common -DHAVE_CONFIG_H -I. -I. -I../../gcc/gcc -I../../gcc/gcc/. -I../../g cc/gcc/../include -I../../gcc/gcc/../libcpp/include -I../../gcc/gcc/../libdecnu mber -I../../gcc/gcc/../libdecnumber/dpd -I../libdecnumber -I../../gcc/gcc/../li bbacktrace ../../gcc/gcc/stor-layout.c -o stor-layout.o../../gcc/gcc/stor-layout.c: In member function ãbool bit_field_mode_iterator::n ext_mode(machine_mode*)ã: ../../gcc/gcc/stor-layout.c:2690:43: error: comparison between signed and unsign ed integer expressions [-Werror=sign-compare] if (start + unit > bitregion_end_ + 1) ^ cc1plus: all warnings being treated as errors Dave
John David Anglin writes: > On Sun, 18 Nov 2012, Richard Sandiford wrote: > > > HOST_WIDE_INT start = bitpos_ - (bitpos_ % unit); > > if (bitregion_start_ && start < bitregion_start_) > > break; > > - if (bitregion_end_ && start + unit > bitregion_end_ + 1) > > + if (start + unit > bitregion_end_ + 1) > > This causes: > > /home/dave/gnu/gcc/objdir/./prev-gcc/g++ -B/home/dave/gnu/gcc/objdir/./prev-gcc/ -B/home/dave/opt/gnu/gcc/gcc-4.8.0/hppa-linux-gnu/bin/ -nostdinc++ -B/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/src/.libs -B/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/libsupc++/.libs -I/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/include/hppa-linux-gnu -I/home/dave/gnu/gcc > /objdir/prev-hppa-linux-gnu/libstdc++-v3/include -I/home/dave/gnu/gcc/gcc/libstdc++-v3/libsupc++ -L/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/sr > c/.libs -L/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/libsupc++/.libs -c -g -O2 -DIN_GCC -fno-exceptions -fno-rtti -fasynchronous-unwind-tabl > es -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wmissing-format-attribut > e -pedantic -Wno-long-long -Wno-variadic-macros -Wno-overlength-strings -Werror > -fno-common -DHAVE_CONFIG_H -I. -I. -I../../gcc/gcc -I../../gcc/gcc/. -I../../g > cc/gcc/../include -I../../gcc/gcc/../libcpp/include -I../../gcc/gcc/../libdecnu > mber -I../../gcc/gcc/../libdecnumber/dpd -I../libdecnumber -I../../gcc/gcc/../li > bbacktrace ../../gcc/gcc/stor-layout.c -o stor-layout.o../../gcc/gcc/stor-layout.c: In member function ãbool bit_field_mode_iterator::n > ext_mode(machine_mode*)ã: > ../../gcc/gcc/stor-layout.c:2690:43: error: comparison between signed and unsign > ed integer expressions [-Werror=sign-compare] > if (start + unit > bitregion_end_ + 1) > ^ > cc1plus: all warnings being treated as errors This error also breaks m68k-linux bootstrap. HWI32 issue?
Index: gcc/stor-layout.c =================================================================== --- gcc/stor-layout.c 2012-11-18 17:26:31.159273478 +0000 +++ gcc/stor-layout.c 2012-11-18 17:28:17.481177253 +0000 @@ -2646,6 +2646,13 @@ fixup_unsigned_type (tree type) bitregion_end_ (bitregion_end), align_ (MIN (align, BIGGEST_ALIGNMENT)), volatilep_ (volatilep), count_ (0) { + if (!bitregion_end_) + { + /* We can assume that any aligned chunk of ALIGN_ bits that overlaps + the bitfield is mapped and won't trap. */ + bitregion_end_ = bitpos + bitsize + align_ - 1; + bitregion_end_ -= bitregion_end_ % align_ + 1; + } } /* Calls to this function return successively larger modes that can be used @@ -2676,23 +2683,15 @@ bit_field_mode_iterator::next_mode (enum if (count_ > 0 && unit > BITS_PER_WORD) break; - /* Stop if the mode is wider than the alignment of the containing - object. - - It is tempting to omit the following line unless STRICT_ALIGNMENT - is true. But that is incorrect, since if the bitfield uses part - of 3 bytes and we use a 4-byte mode, we could get a spurious segv - if the extra 4th byte is past the end of memory. - (Though at least one Unix compiler ignores this problem: - that on the Sequent 386 machine. */ - if (unit > align_) - break; - /* Stop if the mode goes outside the bitregion. */ HOST_WIDE_INT start = bitpos_ - (bitpos_ % unit); if (bitregion_start_ && start < bitregion_start_) break; - if (bitregion_end_ && start + unit > bitregion_end_ + 1) + if (start + unit > bitregion_end_ + 1) + break; + + /* Stop if the mode requires too much alignment. */ + if (unit > align_ && SLOW_UNALIGNED_ACCESS (mode_, align_)) break; *out_mode = mode_; @@ -2751,6 +2750,62 @@ get_best_mode (int bitsize, int bitpos, enum machine_mode widest_mode = VOIDmode; enum machine_mode mode; while (iter.next_mode (&mode) + /* ??? For historical reasons, reject modes that are wider than + the alignment. This has both advantages and disadvantages. + Removing this check means that something like: + + struct s { unsigned int x; unsigned int y; }; + int f (struct s *s) { return s->x == 0 && s->y == 0; } + + can be implemented using a single load and compare on + 64-bit machines that have no alignment restrictions. + For example, on powerpc64-linux-gnu, we would generate: + + ld 3,0(3) + cntlzd 3,3 + srdi 3,3,6 + blr + + rather than: + + lwz 9,0(3) + cmpwi 7,9,0 + bne 7,.L3 + lwz 3,4(3) + cntlzw 3,3 + srwi 3,3,5 + extsw 3,3 + blr + .p2align 4,,15 + .L3: + li 3,0 + blr + + However, accessing more than one field can make life harder + for the gimple optimizers. For example, gcc.dg/vect/bb-slp-5.c + has a series of unsigned short copies followed by a series of + unsigned short comparisons. With this check, both the copies + and comparisons remain 16-bit accesses and FRE is able + to eliminate the latter. Without the check, the comparisons + can be done using 2 64-bit operations, which FRE isn't able + to handle in the same way. + + Either way, it would probably be worth disabling this check + during expand. One particular example where removing the + check would help is the get_best_mode call in store_bit_field. + If we are given a memory bitregion of 128 bits that is aligned + to a 64-bit boundary, and the bitfield we want to modify is + in the second half of the bitregion, this check causes + store_bitfield to turn the memory into a 64-bit reference + to the _first_ half of the region. We later use + adjust_bitfield_address to get a reference to the correct half, + but doing so looks to adjust_bitfield_address as though we are + moving past the end of the original object, so it drops the + associated MEM_EXPR and MEM_OFFSET. Removing the check + causes store_bit_field to keep a 128-bit memory reference, + so that the final bitfield reference still has a MEM_EXPR + and MEM_OFFSET. */ + && GET_MODE_BITSIZE (mode) <= align && (largest_mode == VOIDmode || GET_MODE_SIZE (mode) <= GET_MODE_SIZE (largest_mode))) {