diff options
Diffstat (limited to 'gcc/expr.c')
| -rw-r--r-- | gcc/expr.c | 35 |
1 files changed, 28 insertions, 7 deletions
diff --git a/gcc/expr.c b/gcc/expr.c index 56ec3fa8e2a..6caee3be7ac 100644 --- a/gcc/expr.c +++ b/gcc/expr.c @@ -4431,19 +4431,22 @@ optimize_bitfield_assignment_op (unsigned HOST_WIDE_INT bitsize, /* In the C++ memory model, consecutive bit fields in a structure are considered one memory location. - Given a COMPONENT_REF EXP at bit position BITPOS, this function + Given a COMPONENT_REF EXP at position (BITPOS, OFFSET), this function returns the bit range of consecutive bits in which this COMPONENT_REF - belongs in. The values are returned in *BITSTART and *BITEND. - If the access does not need to be restricted 0 is returned in + belongs. The values are returned in *BITSTART and *BITEND. *BITPOS + and *OFFSET may be adjusted in the process. + + If the access does not need to be restricted, 0 is returned in both *BITSTART and *BITEND. */ static void get_bit_range (unsigned HOST_WIDE_INT *bitstart, unsigned HOST_WIDE_INT *bitend, tree exp, - HOST_WIDE_INT bitpos) + HOST_WIDE_INT *bitpos, + tree *offset) { - unsigned HOST_WIDE_INT bitoffset; + HOST_WIDE_INT bitoffset; tree field, repr; gcc_assert (TREE_CODE (exp) == COMPONENT_REF); @@ -4490,7 +4493,25 @@ get_bit_range (unsigned HOST_WIDE_INT *bitstart, bitoffset += (tree_low_cst (DECL_FIELD_BIT_OFFSET (field), 1) - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1)); - *bitstart = bitpos - bitoffset; + /* If the adjustment is larger than bitpos, we would have a negative bit + position for the lower bound and this may wreak havoc later. This can + occur only if we have a non-null offset, so adjust offset and bitpos + to make the lower bound non-negative. */ + if (bitoffset > *bitpos) + { + HOST_WIDE_INT adjust = bitoffset - *bitpos; + + gcc_assert ((adjust % BITS_PER_UNIT) == 0); + gcc_assert (*offset != NULL_TREE); + + *bitpos += adjust; + *offset + = size_binop (MINUS_EXPR, *offset, size_int (adjust / BITS_PER_UNIT)); + *bitstart = 0; + } + else + *bitstart = *bitpos - bitoffset; + *bitend = *bitstart + tree_low_cst (DECL_SIZE (repr), 1) - 1; } @@ -4595,7 +4616,7 @@ expand_assignment (tree to, tree from, bool nontemporal) if (TREE_CODE (to) == COMPONENT_REF && DECL_BIT_FIELD_TYPE (TREE_OPERAND (to, 1))) - get_bit_range (&bitregion_start, &bitregion_end, to, bitpos); + get_bit_range (&bitregion_start, &bitregion_end, to, &bitpos, &offset); /* If we are going to use store_bit_field and extract_bit_field, make sure to_rtx will be safe for multiple use. */ |