| Message ID | 13270277.uLZWGnKmhe@fomalhaut |
|---|---|
| State | New |
| Headers | show |
| Series | Fix handling of non-integral bit-fields in native_encode_initializer | expand |
On Mon, May 22, 2023 at 10:10 AM Eric Botcazou via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > Hi, > > the encoder for CONSTRUCTORs assumes that all bit-fields (DECL_BIT_FIELD) have > integral types, but that's not the case in Ada where they may have pretty much > any type, resulting in a wrong encoding for them. > > The attached fix filters out non-integral bit-fields, except if they start and > end on a byte boundary because they are correctly handled in this case. > > Bootstrapped/regtested on x86-64/Linux, OK for mainline and 13 branch? OK. Can we handle non-integer bitfields by recursing with a temporary buffer to encode it byte-aligned and then apply shifting and masking to get it in place? Or is that not worth it? Thanks, Richard. > > > 2023-05-22 Eric Botcazou <ebotcazou@adacore.com> > > * fold-const.cc (native_encode_initializer) <CONSTRUCTOR>: Apply the > specific treatment for bit-fields only if they have an integral type > and filter out non-integral bit-fields that do not start and end on > a byte boundary. > > > 2023-05-22 Eric Botcazou <ebotcazou@adacore.com> > > * gnat.dg/opt101.adb: New test. > * gnat.dg/opt101_pkg.ads: New helper. > > -- > Eric Botcazou
> OK. Thanks! > Can we handle non-integer bitfields by recursing with a temporary buffer to > encode it byte-aligned and then apply shifting and masking to get it in > place? Or is that not worth it? Certainly doable, something along these lines is implemented in varasm.c to output these non-integral bit-fields (output_constructor et al) so we could even try to share some code. However, in practice, these cases turn out to be rare because the tree_output_constant_def path in gimplify_init_constructor is well guarded.
diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc index 25466e97220..57521501fff 100644 --- a/gcc/fold-const.cc +++ b/gcc/fold-const.cc @@ -8360,20 +8360,26 @@ native_encode_initializer (tree init, unsigned char *ptr, int len, if (fieldsize == 0) continue; + /* Prepare to deal with integral bit-fields and filter out other + bit-fields that do not start and end on a byte boundary. */ if (DECL_BIT_FIELD (field)) { if (!tree_fits_uhwi_p (DECL_FIELD_BIT_OFFSET (field))) return 0; - fieldsize = TYPE_PRECISION (TREE_TYPE (field)); bpos = tree_to_uhwi (DECL_FIELD_BIT_OFFSET (field)); - if (bpos % BITS_PER_UNIT) - bpos %= BITS_PER_UNIT; - else - bpos = 0; - fieldsize += bpos; - epos = fieldsize % BITS_PER_UNIT; - fieldsize += BITS_PER_UNIT - 1; - fieldsize /= BITS_PER_UNIT; + if (INTEGRAL_TYPE_P (TREE_TYPE (field))) + { + bpos %= BITS_PER_UNIT; + fieldsize = TYPE_PRECISION (TREE_TYPE (field)) + bpos; + epos = fieldsize % BITS_PER_UNIT; + fieldsize += BITS_PER_UNIT - 1; + fieldsize /= BITS_PER_UNIT; + } + else if (bpos % BITS_PER_UNIT + || DECL_SIZE (field) == NULL_TREE + || !tree_fits_shwi_p (DECL_SIZE (field)) + || tree_to_shwi (DECL_SIZE (field)) % BITS_PER_UNIT) + return 0; } if (off != -1 && pos + fieldsize <= off) @@ -8382,7 +8388,8 @@ native_encode_initializer (tree init, unsigned char *ptr, int len, if (val == NULL_TREE) continue; - if (DECL_BIT_FIELD (field)) + if (DECL_BIT_FIELD (field) + && INTEGRAL_TYPE_P (TREE_TYPE (field))) { /* FIXME: Handle PDP endian. */ if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN)