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This patch fixes a bug in the bswap pass.

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This patch fixes a bug in the bswap pass.  In big-endian BIT_FIELD_REF uses
big-endian bit numbering so we need to adjust the bit position.
The existing version could potentially generate incorrect code however GCC
doesn't emit a BIT_FIELD_REF to access the low byte in a register, so the
symbolic number never matches in big-endian.

    gcc/
	* tree-ssa-math-opts.c (find_bswap_or_nop_1): Adjust bitnumbering
	for big-endian BIT_FIELD_REF.

From-SVN: r237822
This commit is contained in:
Wilco Dijkstra 2016-06-28 13:57:47 +00:00 • committed by Wilco Dijkstra
parent eda328bf1d
commit f6922a5660
2 changed files with 9 additions and 0 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2016-06-28 Wilco Dijkstra <wdijkstr@arm.com>
* tree-ssa-math-opts.c (find_bswap_or_nop_1): Adjust bitnumbering
for big-endian BIT_FIELD_REF.
2016-06-28 Pat Haugen <pthaugen@us.ibm.com>
* config/rs6000/rs6000.md ('type' attribute): Add htmsimple/dfp types.

4
gcc/tree-ssa-math-opts.c
View file

@ -2307,6 +2307,10 @@ find_bswap_or_nop_1 (gimple *stmt, struct symbolic_number *n, int limit)
&& bitsize % BITS_PER_UNIT == 0
&& init_symbolic_number (n, TREE_OPERAND (rhs1, 0)))
{
/* Handle big-endian bit numbering in BIT_FIELD_REF. */
if (BYTES_BIG_ENDIAN)
bitpos = TYPE_PRECISION (n->type) - bitpos - bitsize;
/* Shift. */
if (!do_shift_rotate (RSHIFT_EXPR, n, bitpos))
return NULL;