From: wilco <wilco@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Tue, 28 Jun 2016 13:57:47 +0000 (+0000)
Subject: This patch fixes a bug in the bswap pass.  In big-endian BIT_FIELD_REF uses
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=e5c957b427075452786ddd4fda684fd27cffafc0;p=thirdparty%2Fgcc.git

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.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@237822 138bc75d-0d04-0410-961f-82ee72b054a4
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f88c40470e31..d9d41ad9ec1c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -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.
diff --git a/gcc/tree-ssa-math-opts.c b/gcc/tree-ssa-math-opts.c
index 513ef0b3f4eb..d31c12fd818a 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;