On Mon, May 7, 2012 at 10:00 AM, Jakub Jelinek <[email protected]> wrote:
>> > Shouldn't that be done only for generic tuning? If somebody uses
>> > -mtune=native, then emitting rep; bsf is overkill, the code is intended
>> > to be run on a CPU without (or with TARGET_BMI with) tzcnt insn support.
>>
>> Yes, this is a good idea.
>>
>> Something like attached patch?
>
> Yeah, but probably with the TARGET_BMI and optimize_function_for_size_p
> lines swapped.
>
> Because i386.h defines
> CTZ_DEFINED_VALUE_AT_ZERO to 1 for TARGET_BMI, therefore it isn't
> undefined for TARGET_BMI, so even for -Os you can't just use bsf.
I have committed following patch:
2012-05-07 Uros Bizjak <[email protected]>
* config/i386/i386.md (ctz<mode>2): Emit rep;bsf
only for TARGET_GENERIC, when not optimizing for size.
(*ffs<mode>_1): Ditto.
Tested on x86_64-pc-linux-gnu {,-m32}.
Uros.
Index: i386.md
===================================================================
--- i386.md (revision 187223)
+++ i386.md (working copy)
@@ -12113,21 +12113,25 @@
(ctz:SWI48 (match_dup 1)))]
""
{
- if (optimize_function_for_size_p (cfun))
- return "bsf{<imodesuffix>}\t{%1, %0|%0, %1}";
- else if (TARGET_BMI)
+ if (TARGET_BMI)
return "tzcnt{<imodesuffix>}\t{%1, %0|%0, %1}";
- else
+ 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}";
+
+ return "bsf{<imodesuffix>}\t{%1, %0|%0, %1}";
}
[(set_attr "type" "alu1")
(set_attr "prefix_0f" "1")
(set (attr "prefix_rep")
(if_then_else
- (match_test "optimize_function_for_size_p (cfun)")
- (const_string "0")
- (const_string "1")))
+ (ior (match_test "TARGET_BMI")
+ (and (not (match_test "optimize_function_for_size_p (cfun)"))
+ (match_test "TARGET_GENERIC")))
+ (const_string "1")
+ (const_string "0")))
(set_attr "mode" "<MODE>")])
(define_insn "ctz<mode>2"
@@ -12136,21 +12140,25 @@
(clobber (reg:CC FLAGS_REG))]
""
{
- if (optimize_function_for_size_p (cfun))
- return "bsf{<imodesuffix>}\t{%1, %0|%0, %1}";
- else if (TARGET_BMI)
+ if (TARGET_BMI)
return "tzcnt{<imodesuffix>}\t{%1, %0|%0, %1}";
- else
+ 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}";
+
+ return "bsf{<imodesuffix>}\t{%1, %0|%0, %1}";
}
[(set_attr "type" "alu1")
(set_attr "prefix_0f" "1")
(set (attr "prefix_rep")
(if_then_else
- (match_test "optimize_function_for_size_p (cfun)")
- (const_string "0")
- (const_string "1")))
+ (ior (match_test "TARGET_BMI")
+ (and (not (match_test "optimize_function_for_size_p (cfun)"))
+ (match_test "TARGET_GENERIC")))
+ (const_string "1")
+ (const_string "0")))
(set_attr "mode" "<MODE>")])
(define_expand "clz<mode>2"
