[ARM] Use UBFX for some and-immediate operations

[ARM] Use UBFX for some and-immediate operations

[Richard Earnshaw]

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This patch adds the ability to spot and exploit the UBFX instruction
(bit-field extract) to perform AND operations with an immediate which is
2^N - 1.  On some benchmarks this can lead to a significant win over the
existing behaviour on Cortex-A15.

Tested on arm-eabi with some additional testing on arm-linux-gnueabi
platforms.

R.

2012-08-02  Richard Earnshaw  <rearnsha@arm.com>

	* arm.c (arm_gen_constant): Use UBFX for some AND operations when
	available.

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--- arm.c	(revision 190101)
+++ arm.c	(local)
@@ -2982,6 +2982,31 @@ arm_gen_constant (enum rtx_code code, en
       return 1;
     }
 
+  /* On targets with UXTH/UBFX, we can deal with AND (2^N)-1 in a single
+     insn.  */
+  if (code == AND && (i = exact_log2 (remainder + 1)) > 0
+      && (arm_arch_thumb2 || (i == 16 && arm_arch6 && mode == SImode)))
+    {
+      if (generate)
+	{
+	  if (mode == SImode && i == 16)
+	    /* Use UXTH in preference to UBFX, since on Thumb2 it's a 
+	       smaller insn.  */
+	    emit_constant_insn (cond,
+				gen_zero_extendhisi2
+				(target, gen_lowpart (HImode, source)));
+	  else
+	    /* Extz only supports SImode, but we can coerce the operands
+	       into that mode.  */
+	    emit_constant_insn (cond,
+				gen_extzv_t2 (gen_lowpart (mode, target),
+					      gen_lowpart (mode, source),
+					      GEN_INT (i), const0_rtx));
+	}
+
+      return 1;
+    }
+
   /* Calculate a few attributes that may be useful for specific
      optimizations.  */
   /* Count number of leading zeros.  */

Re: [ARM] Use UBFX for some and-immediate operations

[Richard Henderson]

On 2012-08-02 09:24, Richard Earnshaw wrote:
> +	    /* Extz only supports SImode, but we can coerce the operands
> +	       into that mode.  */
> +	    emit_constant_insn (cond,
> +				gen_extzv_t2 (gen_lowpart (mode, target),
> +					      gen_lowpart (mode, source),
> +					      GEN_INT (i), const0_rtx));

Didn't you mean gen_lowpart (SImode, ...) ?


r~

Re: [ARM] Use UBFX for some and-immediate operations

[Richard Earnshaw]

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On 03/08/12 19:10, Richard Henderson wrote:
> On 2012-08-02 09:24, Richard Earnshaw wrote:
>> +	    /* Extz only supports SImode, but we can coerce the operands
>> +	       into that mode.  */
>> +	    emit_constant_insn (cond,
>> +				gen_extzv_t2 (gen_lowpart (mode, target),
>> +					      gen_lowpart (mode, source),
>> +					      GEN_INT (i), const0_rtx));
> 
> Didn't you mean gen_lowpart (SImode, ...) ?
> 
> 
> r~
> 

Urm, yes.  Well spotted.

Fixed thusly:

2012-08-04  Richard Earnshaw  <rearnsha@arm.com>

	* arm.c (arm_gen_constant): Use SImode when preparing operands for
	gen_extzv_t2.


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--- arm.c	(revision 190143)
+++ arm.c	(local)
@@ -2999,8 +2999,8 @@ arm_gen_constant (enum rtx_code code, en
 	    /* Extz only supports SImode, but we can coerce the operands
 	       into that mode.  */
 	    emit_constant_insn (cond,
-				gen_extzv_t2 (gen_lowpart (mode, target),
-					      gen_lowpart (mode, source),
+				gen_extzv_t2 (gen_lowpart (SImode, target),
+					      gen_lowpart (SImode, source),
 					      GEN_INT (i), const0_rtx));
 	}