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 <rearn...@arm.com>
* arm.c (arm_gen_constant): Use UBFX for some AND operations when
available.--- 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. */
