Re: [off list] Re: [PATCH] x86: use 'rep bsf' syntax when assembler supports it

[Roland McGrath]

Here is an alternative patch that just changes the configure test
controlling %; so it will elide the ; only for an assembler that
also accepts 'rep bsf', 'rep bsr', and 'rep ret', and just uses
%; for these cases too.  You'll need to have built binutils from its trunk
within the last five minutes or so to have an assembler that passes the
test now.


Thanks,
Roland


gcc/
2012-06-22  Roland McGrath  <mcgra...@google.com>

        * configure.ac (HAVE_AS_IX86_REP_LOCK_PREFIX): Also require that the
        assembler accept 'rep bsf ...', 'rep bsr ...', and 'rep ret'.
        * configure: Regenerated.
        * config/i386/i386.md (simple_return_internal_long): Use %;
        (ctz<mode>2): Likewise.

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 879b87b..16056c1 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -11902,7 +11902,7 @@
   [(simple_return)
    (unspec [(const_int 0)] UNSPEC_REP)]
   "reload_completed"
-  "rep\;ret"
+  "rep%; ret"
   [(set_attr "length" "2")
    (set_attr "atom_unit" "jeu")
    (set_attr "length_immediate" "0")
@@ -12234,8 +12234,8 @@
   else if (optimize_function_for_size_p (cfun))
     ;
   else if (TARGET_GENERIC)
-    /* tzcnt expands to rep;bsf and we can use it even if !TARGET_BMI.  */
-    return "rep; bsf{<imodesuffix>}\t{%1, %0|%0, %1}";
+    /* tzcnt expands to 'rep bsf' and we can use it even if !TARGET_BMI.  */
+    return "rep%; bsf{<imodesuffix>}\t{%1, %0|%0, %1}";

   return "bsf{<imodesuffix>}\t{%1, %0|%0, %1}";
 }
diff --git a/gcc/configure b/gcc/configure
index 1fdf0af..5e8107f 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -24791,7 +24791,10 @@ else
   if test x$gcc_cv_as != x; then
     $as_echo 'rep movsl
         lock addl %edi, (%eax,%esi)
-        lock orl $0, (%esp)' > conftest.s
+        lock orl $0, (%esp)
+        rep bsf %ecx, %eax
+        rep bsr %ecx, %eax
+        rep ret' > conftest.s
     if { ac_try='$gcc_cv_as $gcc_cv_as_flags  -o conftest.o conftest.s >&5'
   { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
   (eval $ac_try) 2>&5
@@ -28698,4 +28701,3 @@ if test -n "$ac_unrecognized_opts" && test
"$enable_option_checking" != no; then
 $as_echo "$as_me: WARNING: unrecognized options: $ac_unrecognized_opts" >&2;}
 fi

-
diff --git a/gcc/configure.ac b/gcc/configure.ac
index 22dab55..428a21a 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -3642,7 +3642,10 @@ foo:     nop
         gcc_cv_as_ix86_rep_lock_prefix,,,
        [rep movsl
         lock addl %edi, (%eax,%esi)
-        lock orl $0, (%esp)],,
+        lock orl $0, (%esp)
+        rep bsf %ecx, %eax
+        rep bsr %ecx, %eax
+        rep ret],,
         [AC_DEFINE(HAVE_AS_IX86_REP_LOCK_PREFIX, 1,
           [Define if the assembler supports 'rep <insn>, lock <insn>'.])])

@@ -5163,4 +5166,3 @@ done
 ],
 [subdirs='$subdirs'])
 AC_OUTPUT
-