A lot of old user code clobbers the carry bit without telling the compiler
about it. This used to just work, because the compiler never used the bit
outside of a single RTL instruction. But that will change. Let's clobber
the carry bit in every asm; this isn't very expensive.
2014-12-08 Segher Boessenkool <seg...@kernel.crashing.org>
gcc/
PR target/64180
* config/rs6000/rs6000.c (TARGET_MD_ASM_CLOBBERS): Define.
(rs6000_md_asm_clobbers): New function.
---
gcc/config/rs6000/rs6000.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index cdb9de9..e58fc81 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -1556,6 +1556,9 @@ static const struct attribute_spec
rs6000_attribute_table[] =
#undef TARGET_ASM_LOOP_ALIGN_MAX_SKIP
#define TARGET_ASM_LOOP_ALIGN_MAX_SKIP rs6000_loop_align_max_skip
+#undef TARGET_MD_ASM_CLOBBERS
+#define TARGET_MD_ASM_CLOBBERS rs6000_md_asm_clobbers
+
#undef TARGET_OPTION_OVERRIDE
#define TARGET_OPTION_OVERRIDE rs6000_option_override
@@ -3146,6 +3149,19 @@ rs6000_builtin_mask_calculate (void)
| ((TARGET_LONG_DOUBLE_128) ? RS6000_BTM_LDBL128 : 0));
}
+/* Implement TARGET_MD_ASM_CLOBBERS. All asm statements are considered
+ to clobber the XER[CA] bit because clobbering that bit without telling
+ the compiler worked just fine with versions of GCC before GCC 5, and
+ breaking a lot of older code in ways that are hard to track down is
+ not such a great idea. */
+
+static tree
+rs6000_md_asm_clobbers (tree, tree, tree clobbers)
+{
+ tree s = build_string (strlen (reg_names[CA_REGNO]), reg_names[CA_REGNO]);
+ return tree_cons (NULL_TREE, s, clobbers);
+}
+
/* Override command line options. Mostly we process the processor type and
sometimes adjust other TARGET_ options. */
--
1.8.1.4
