[PATCH 01/10] rs6000: Clobber XER[CA] in all user asm statements

[Segher Boessenkool <segher at kernel dot crashing dot org>]

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  <segher@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