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.
The test gcc.dg/optimize-bswapsi-4.c now passes on AArch64, no other changes.
OK for commit?
ChangeLog:
2016-06-23 Wilco Dijkstra <wdijk...@arm.com>
* gcc/tree-ssa-math-opts.c (find_bswap_or_nop_1): Adjust bitnumbering
for big-endian BIT_FIELD_REF.
--
diff --git a/gcc/tree-ssa-math-opts.c b/gcc/tree-ssa-math-opts.c
index
513ef0b3f4eb29a35eae8a0eb14ee8f8c24fcfd9..d31c12fd818a713ca3d251b9464015b147235bbe
100644
--- a/gcc/tree-ssa-math-opts.c
+++ b/gcc/tree-ssa-math-opts.c
@@ -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;
