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Re: The arm patch 161344 to transform TST into LSLS


Hi Richard

The following patch has been tested on arm qemu. Could you take a look?

thanks
Guozhi

ChangeLog:
2010-07-02  Wei Guozhi  <carrot@google.com>

        * thumb2.md (peephole2 to convert zero_extract/compare of lowest bits
        to lshift/compare): New.


Index: thumb2.md
===================================================================
--- thumb2.md   ïrevision 161725ï
+++ thumb2.md   ïworking copyï
@@ -1501,3 +1501,29 @@
                                VOIDmode, operands[0], const0_rtx);
   ")

+(define_peephole2
+  [(set (match_operand:CC_NOOV 0 "cc_register" "")
+       (compare:CC_NOOV (zero_extract:SI
+                         (match_operand:SI 1 "low_register_operand" "")
+                         (match_operand:SI 2 "const_int_operand" "")
+                         (const_int 0))
+                        (const_int 0)))
+   (match_scratch:SI 3 "l")
+   (set (pc)
+       (if_then_else (match_operator:CC_NOOV 4 "equality_operator"
+                      [(match_dup 0) (const_int 0)])
+                     (match_operand 5 "" "")
+                     (match_operand 6 "" "")))]
+  "TARGET_THUMB2
+   && (INTVAL (operands[2]) > 0 && INTVAL (operands[2]) <= 32)"
+  [(parallel [(set (match_dup 0)
+                  (compare:CC_NOOV (ashift:SI (match_dup 1) (match_dup 2))
+                                   (const_int 0)))
+             (clobber (match_dup 3))])
+   (set (pc)
+       (if_then_else (match_op_dup 4 [(match_dup 0) (const_int 0)])
+                     (match_dup 5) (match_dup 6)))]
+  "
+  operands[2] = GEN_INT (32 - INTVAL (operands[2]));
+  ")
+

On Fri, Jul 2, 2010 at 5:15 PM, Richard Earnshaw <rearnsha@arm.com> wrote:
>
> On Fri, 2010-07-02 at 08:53 +0800, Carrot Wei wrote:
>> Hi Richard
>>
>> The new peephole2 and the old pattern does different optimization. As
>> you have described the peephole2 can optimize the cases that test a
>> single bit in a word. But the old pattern tests if the bit fields at
>> the low end of a word is equal or not equal to zero, the bit field may
>> contain more than 1 bit. Interestingly the test case with the old
>> pattern can fit in both situations. If we change the test case as
>> following, it can show the regression.
>>
>> struct A
>> {
>> Â int v:2;
>> };
>>
>>
>> int bar();
>> int foo(struct A* p)
>> {
>> Â if (p->v)
>> Â Â return 1;
>> Â return bar();
>> }
>>
>> So we need another peephole2 to bring that optimization back.
>>
>> thanks
>> Guozhi
>
> Yes, a peep2 for that should be pretty straight-forward to generate.
> Simply transform the code into a left-shift and compare with 0, then a
> branch if eq/ne.
>
> R.
>
>


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