Re: [PATCH v3] Simplify memchr with small constant strings

[Jan-Benedict Glaw <jbglaw@lug-owl.de>]

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Hi!

On Wed, 2022-07-13 09:50:14 -0700, H.J. Lu via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> When memchr is applied on a constant string of no more than the bytes of
> a word, simplify memchr by checking each byte in the constant string.
> 
> int f (int a)
> {
>    return  __builtin_memchr ("AE", a, 2) != 0;
> }
> 
> is simplified to
> 
> int f (int a)
> {
>   return ((char) a == 'A' || (char) a == 'E') != 0;
> }

Seems this caused a regression for --target=avr-elf, pru-elf and
rl78-elf:

.../gcc/configure --prefix=... --enable-werror-always --enable-languages=all --disable-gcov --disable-shared --disable-threads --target=pru-elf --without-headers
[...]
make V=1 all-gcc
[...]
/usr/lib/gcc-snapshot/bin/g++  -fno-PIE -c   -g -O2   -DIN_GCC  -DCROSS_DIRECTORY_STRUCTURE   -fno-exceptions -fno-rtti -fasynchronous-unwind-tables -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wmissing-format-attribute -Woverloaded-virtual -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../../gcc/gcc/../include -I../../gcc/gcc/../libcpp/include -I../../gcc/gcc/../libcody  -I../../gcc/gcc/../libdecnumber -I../../gcc/gcc/../libdecnumber/dpd -I../libdecnumber -I../../gcc/gcc/../libbacktrace   -o tree-ssa-forwprop.o -MT tree-ssa-forwprop.o -MMD -MP -MF ./.deps/tree-ssa-forwprop.TPo ../../gcc/gcc/tree-ssa-forwprop.cc
../../gcc/gcc/tree-ssa-forwprop.cc: In function 'bool simplify_builtin_call(gimple_stmt_iterator*, tree)':
../../gcc/gcc/tree-ssa-forwprop.cc:1258:42: error: array subscript 1 is outside array bounds of 'tree_node* [1]' [-Werror=array-bounds]
 1258 |             op[i - 1] = fold_convert_loc (loc, boolean_type_node,
      |                         ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
 1259 |                                           fold_build2_loc (loc,
      |                                           ~~~~~~~~~~~~~~~~~~~~~
 1260 |                                                            BIT_IOR_EXPR,
      |                                                            ~~~~~~~~~~~~~
 1261 |                                                            boolean_type_node,
      |                                                            ~~~~~~~~~~~~~~~~~~
 1262 |                                                            op[i - 1],
      |                                                            ~~~~~~~~~~
 1263 |                                                            op[i]));
      |                                                            ~~~~~~~
In file included from ../../gcc/gcc/system.h:707,
                 from ../../gcc/gcc/tree-ssa-forwprop.cc:21:
../../gcc/gcc/../include/libiberty.h:733:36: note: at offset 8 into object of size [0, 8] allocated by '__builtin_alloca'
  733 | # define alloca(x) __builtin_alloca(x)
      |                    ~~~~~~~~~~~~~~~~^~~
../../gcc/gcc/../include/libiberty.h:365:40: note: in expansion of macro 'alloca'
  365 | #define XALLOCAVEC(T, N)        ((T *) alloca (sizeof (T) * (N)))
      |                                        ^~~~~~
../../gcc/gcc/tree-ssa-forwprop.cc:1250:22: note: in expansion of macro 'XALLOCAVEC'
 1250 |           tree *op = XALLOCAVEC (tree, isize);
      |                      ^~~~~~~~~~
cc1plus: all warnings being treated as errors
make[1]: *** [Makefile:1146: tree-ssa-forwprop.o] Error 1
make[1]: Leaving directory '/var/lib/laminar/run/gcc-pru-elf/1/toolchain-build/gcc'
make: *** [Makefile:4583: all-gcc] Error 2

Thanks,
  Jan-Benedict

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