Fix __sync_val_compare_and_swap_8() on i386 for code compiled with -fPIC.

In some cases GCC would generate a cmpxchg8b instruction with a memory
reference that used %ebx.  This is wrong (and will almost certainly result
in SIGSEGV).  This fix uses a new memory constraint "W" to prevent the use
of %ebx in this case.  This differs from the approach taken by upstream so
there are no GPLv3 issues here.

Fixes the Mesa i965 dri module on i386.

ok jsg@

3 files changed, 34 insertions, 2 deletions

diff --git a/gnu/gcc/gcc/config/i386/constraints.md b/gnu/gcc/gcc/config/i386/constraints.md
index 0ab4995f3b8..149a69878b4 100644
--- a/gnu/gcc/gcc/config/i386/constraints.md
+++ b/gnu/gcc/gcc/config/i386/constraints.md
@@ -150,3 +150,7 @@
    to fit that range (for immediate operands in zero-extending x86-64
    instructions)."
   (match_operand 0 "x86_64_zext_immediate_operand"))
+
+(define_memory_constraint "W"
+  "CMPXCHG8B memory reference."
+  (match_test "cmpxchg8b_mem_constraint (op)"))
diff --git a/gnu/gcc/gcc/config/i386/i386.c b/gnu/gcc/gcc/config/i386/i386.c
index 6fab6d81312..6f77b9ba5a7 100644
--- a/gnu/gcc/gcc/config/i386/i386.c
+++ b/gnu/gcc/gcc/config/i386/i386.c
@@ -4719,6 +4719,34 @@ standard_sse_constant_opcode (rtx insn, rtx x)
   gcc_unreachable ();
 }
 
+int
+cmpxchg8b_mem_constraint (rtx op)
+{
+  struct ix86_address parts;
+
+  if (TARGET_64BIT || !flag_pic)
+    return 1;
+
+  if (GET_CODE (op) != MEM)
+    return 0;
+  if (!ix86_decompose_address (XEXP (op, 0), &parts))
+    return 0;
+
+  if (parts.base && GET_CODE (parts.base) == SUBREG)
+    parts.base = SUBREG_REG (parts.base);
+  if (parts.index && GET_CODE (parts.index) == SUBREG)
+    parts.index = SUBREG_REG (parts.index);
+
+  if (parts.base && REG_P (parts.base)
+      && REGNO_REG_CLASS (REGNO (parts.base)) == BREG)
+    return 0;
+  if (parts.index && REG_P (parts.index)
+      && REGNO_REG_CLASS (REGNO (parts.index)) == BREG)
+    return 0;
+
+  return 1;
+}
+
 /* Returns 1 if OP contains a symbol reference */
 
 int
diff --git a/gnu/gcc/gcc/config/i386/sync.md b/gnu/gcc/gcc/config/i386/sync.md
index 8c2fdb230b0..30566450fa4 100644
--- a/gnu/gcc/gcc/config/i386/sync.md
+++ b/gnu/gcc/gcc/config/i386/sync.md
@@ -109,7 +109,7 @@
 ;; are just esi and edi.
 (define_insn "*sync_double_compare_and_swapdi_pic"
   [(set (match_operand:DI 0 "register_operand" "=A")
-	(match_operand:DI 1 "memory_operand" "+m"))
+	(match_operand:DI 1 "memory_operand" "+W"))
    (set (match_dup 1)
 	(unspec_volatile:DI
 	  [(match_dup 1)
@@ -202,7 +202,7 @@
 ;; operand 3.
 (define_insn "*sync_double_compare_and_swap_ccdi_pic"
   [(set (match_operand:DI 0 "register_operand" "=A")
-	(match_operand:DI 1 "memory_operand" "+m"))
+	(match_operand:DI 1 "memory_operand" "+W"))
    (set (match_dup 1)
 	(unspec_volatile:DI
 	  [(match_dup 1)