[PATCH] Add memory barriers to xbegin/xend/xabort

[Andi Kleen]

From: Andi Kleen <a...@linux.intel.com>

xbegin/xend/xabort were missing memory barriers. This can
lead to memory operations being moved out of transactions, which would
cause unexpected races.

Always generate implicit memory barriers for these intrinsics.

The compat header versions always generated memory barriers,
so this also improves compatibility.

Passes test suite. Ok for release branches?

gcc/:

2014-10-28  Andi Kleen  <a...@linux.intel.com>

        PR target/63672
        * config/i386/i386.c (ix86_expand_builtin): Generate memory
        barrier after abort.
        * config/i386/i386.md (xbegin): Add memory barrier.
        (xend): Rename to ...
        (xend_1): New. Generate memory barrier and emit xend.
---
 gcc/config/i386/i386.c  |  1 +
 gcc/config/i386/i386.md | 18 +++++++++++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index ec3e056..ec0df40 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -36413,6 +36413,7 @@ addcarryx:
          return const0_rtx;
        }
       emit_insn (gen_xabort (op0));
+      emit_insn (gen_memory_blockage ());
       return 0;
 
     default:
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 7ba07c3..3544e60 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -18530,6 +18530,9 @@
 
   emit_move_insn (operands[0], ax_reg);
 
+  operands[0] = gen_rtx_MEM (BLKmode, gen_rtx_SCRATCH (Pmode));
+  MEM_VOLATILE_P (operands[0]) = 1;
+
   DONE;
 })
 
@@ -18546,13 +18549,26 @@
   [(set_attr "type" "other")
    (set_attr "length" "6")])
 
-(define_insn "xend"
+(define_insn "xend_1"
   [(unspec_volatile [(const_int 0)] UNSPECV_XEND)]
   "TARGET_RTM"
   "xend"
   [(set_attr "type" "other")
    (set_attr "length" "3")])
 
+(define_expand "xend"
+  [(set (match_dup 0)
+       (unspec:BLK [(const_int 0)] UNSPECV_XEND))] /* or match_dup 0 ? */
+  "TARGET_RTM"
+{
+  emit_insn (gen_xend_1 ());
+
+  operands[0] = gen_rtx_MEM (BLKmode, gen_rtx_SCRATCH (Pmode));
+  MEM_VOLATILE_P (operands[0]) = 1;
+
+  DONE;
+})
+
 (define_insn "xabort"
   [(unspec_volatile [(match_operand:SI 0 "const_0_to_255_operand" "n")]
                    UNSPECV_XABORT)]
-- 
2.1.1